diff --git a/references/2014_heartbleed.pdf b/references/2014_heartbleed.pdf new file mode 100644 index 0000000..b86ced7 Binary files /dev/null and b/references/2014_heartbleed.pdf differ diff --git a/references/2019_checksec.pdf b/references/2019_checksec.pdf new file mode 100644 index 0000000..60c06db Binary files /dev/null and b/references/2019_checksec.pdf differ diff --git a/work/01paper.pdf b/work/01paper.pdf index 77a6872..73984d4 100644 Binary files a/work/01paper.pdf and b/work/01paper.pdf differ diff --git a/work/01paper.tex b/work/01paper.tex index 173c693..b4e2514 100644 --- a/work/01paper.tex +++ b/work/01paper.tex @@ -27,6 +27,7 @@ %\usepackage[ngerman]{babel} \usepackage[utf8]{inputenc} \usepackage{hyperref} +\usepackage{cleveref} \usepackage{url} %%fuer abkuerzungen begin \usepackage[acronym,hyperfirst = false]{glossaries} @@ -60,7 +61,12 @@ MatrNr. 3220018} \maketitle \begin{abstract} -TODO + + This paper tries to explain the details behind buffer overflows, explore the + problems stemming from those kinds of software vulnerabilities and discus + possible countermeasures with focus on their effectiveness, performance impact + and ease of use. + \end{abstract} \begin{IEEEkeywords} @@ -74,20 +80,24 @@ Buffer Overflow, Software Security When the first programming languages were designed, memory had to be managed manually to make the best use of slow hardware. This opened the door for many kinds of programming errors. Memory can be deallocated more than once -(double-free), the programm could read or write out of bounds of a buffer -(information leaks, \acp{bof}). Languages that are affected by this are e.g. C, -C++ and Fortran. These languages are still used in critical parts of the worlds +(double-free), invalid pointers can be dereferenced (\mintinline{C}{NULL} +pointer dereference; this is still a problem in many modern languages), the +program could read or write out of bounds of a buffer (information leaks, +\acp{bof}). Languages that are affected by this are e.g.\ C, C++ and Fortran. +While most if not all of these problems are solved in modern programming +languages, these languages are still used in critical parts of the worlds infrastructure, either because they allow to implement really performant -programms, because they power legacy systems or for portability reasons. +programs, offer deterministic runtime behaviour (e.g.\ no pauses due to garbage +collection), because they power legacy systems or for portability reasons. Scientists and software engineers have proposed lots of solutions to this problem over the years and this paper aims to compare and give an overview about those. Reading out of bounds can result in an information leak and is less critical -than \acp{bof} in most cases, but there are exceptions, e.g.\ the Heartbleed bug -in OpenSSL which allowed dumping secret keys from memory. Out of bounds writes -are almost always critical and result in code execution vulnerabilities or at -least application crashes. +than \acp{bof} in most cases, but there are exceptions, e.g.\ the Heartbleed +bug~\cite{Heardbleed2014} in OpenSSL which allowed dumping secret keys from +memory. Out of bounds writes are almost always critical and result in code +execution vulnerabilities or at least application crashes. In 2018, 14\% (2368 out of 16556)~\cite{Cve2018} of all software vulnerabilities that have a CVE assigned, were overflow related. This shows that, even if this @@ -95,241 +105,439 @@ type of bug is very old and well known, it's still relevant today. \section{Background}\label{ref:background} -% TODO: many references - \subsection{Technical Details} -Exploitation of \ac{bof} vulnerabilities almost always works by overriding the -return address in the current stack frame, so when the \mintinline{ASM}{RET} -instruction is executed, an attacker controlled address is moved into the -instruction pointer register and the code pointed to by this address is -executed. Other ways include overriding addresses in the \ac{plt} of a binary so -that, if a linked function is called, an attacker controlled function is called -instead, or (in C++) overriding the vtable where the pointers to an object's -methods are stored. +Code execution via \ac{bof} vulnerabilities almost always works by overwriting +the return address in the current stack frame (known as \enquote{stack +smashing})~\cite{Smashing2004}, so when the \mintinline{ASM}{RET} instruction is +executed, an attacker controlled address is moved into the instruction pointer +register and the code pointed to by this address is +executed~\cite{Detection2018}. Other ways include overwriting addresses in the +\ac{plt} (the \ac{plt} contains addresses of dynamically linked library +functions) of a binary so that, if a linked function is called, an attacker +controlled function is called instead, or (in C++) overwriting the vtable where +the pointers to an object's methods are stored. -A simple vulnerable programm might look like this: +A simple vulnerable C program might look like this: +\begin{figure}[h!] \begin{minted}{c} -int main(int argc, char **argv) { +void vuln(char *input) { char buf[50]; - for (size_t i = 0; i < strlen(argv[1]); i++) { - buf[i] = argv[1][i]; + size_t len = strlen(input); + for (size_t i = 0; i < len; i++) { + buf[i] = input[i]; } +} +int main(int argc, char **argv) { + vuln(argv[1]); return 0; } \end{minted} - -A successful exploit would place the payload in the memory by supplying it as an -argument to the programm and eventually overwrite the return address by -providing an input $> 50$ and therefore writing out of bounds. When the -\mintinline{C}{return} instruction is executed, and jumps into the payload, the -attacker's code is executed. This works due to the way, how function calls on -CPUs work. The stack frame of the current function lies between the two pointers -\ac{bp} and \ac{sp} as shown in~\ref{fig:before}. When a function is called, the -value of the \ac{bp}, \ac{sp} and \ac{ip} is pushed to the stack -(Fig.~\ref{fig:call}) and the \ac{ip} is set to the address of the called -function. When the function returns, the old \ac{ip} is restored from the stack -and the execution continues from where the function was called. If an overflow -overwrites the old \ac{ip} (Fig.~\ref{fig:exploit}), the execution continues in -attacker controlled code. - -\begin{figure}[h!] - \includegraphics[width=.3\textwidth]{./dot/before.pdf} - \caption{Stack layout before function call}\label{fig:before} -\end{figure}% - -\begin{figure}[h!] - \includegraphics[width=.3\textwidth]{./dot/call.pdf} - \caption{Stack layout after function call}\label{fig:call} -\end{figure}% - -\begin{figure}[h!] - \includegraphics[width=.3\textwidth]{./dot/exploit.pdf} - \caption{Stack layout after overflow}\label{fig:exploit} +\caption{Vulnerable C program}\label{lst:vuln} \end{figure} -This is only one of several types and exploitation techniques but the general -idea stays the same: ovewrite the return address or some kind of function -pointer (e.g.\ in vtables or the \ac{plt}) and once that function is called, the -execution flow is hijacked and the attacker can execute arbitiary code. +A successful stack \ac{bof} exploit would place the payload in the memory by +supplying it as an argument to the program (or by placing it in an environment +variable, writing it to a file that the program reads, via network packet, ...) +and eventually overwrite the return address by providing an input with $> 50$ +bytes and therefore writing out of bounds. When executing the +\mintinline{C}{return} instruction, and the jumps into the payload, the +attacker's code is executed. This works due to the way, how function calls on +CPUs work: The stack frame of the current function lies between the \ac{bp} and +\ac{sp} as shown in~\cref{fig:before}. When a function is called, the value +of the \ac{bp} and \ac{ip} is pushed to the stack (\cref{fig:call}) and the +\ac{ip} is set to the address of the called function. When the function returns, +the old \ac{ip} is restored from the stack and the execution continues from +where the function was called. If an overflow overwrites the old \ac{ip} +(\cref{fig:exploit}), the attacker controls where execution continues. -The most trivial kinds of exploits is known as a \mintinline{ASM}{NOP} sled. +\begin{figure}[h!] + \begin{subfigure}[b]{.3\textwidth} + \includegraphics[width=\textwidth]{./dot/before.pdf} + \caption{Stack layout before function call}\label{fig:before} + \end{subfigure}\\ + + \begin{subfigure}[b]{.3\textwidth} + \includegraphics[width=\textwidth]{./dot/call.pdf} + \caption{Stack layout after function call}\label{fig:call} + \end{subfigure}\\ + + \begin{subfigure}[b]{.3\textwidth} + \includegraphics[width=\textwidth]{./dot/exploit.pdf} + \caption{Stack layout after overflow}\label{fig:exploit} + \end{subfigure} + \caption{Stack layouts during an \ac{bof} exploit} +\end{figure}% + +This is only one of several types and exploitation techniques. Others include + +\begin{itemize} + + \item Heap-based \ac{bof}: In this case there is no way of overwriting the + return address but objects on the heap might contain function pointers + (e.g.\ for dynamic dispatch) which can be overwritten to execute the + attackers code, when executed~\cite{Detection2018}. + + \item Integer overflow: Some calculation on fixed sized integers is used to + allocate memory. The calculation leads to an integer overflow and only a + small buffer is allocated~\cite{Detection2018}. Later a big integer into the + buffer is used and reads or writes outside the buffer. This kind of + vulnerability can also lead to other problems because at least in C, signed + integer overflow is undefined behaviour. + +\end{itemize} + +This paper won't explore other kinds of \ac{bof} in detail because the concept +is always the same: Unchecked indexing into memory allows the attacker to +overwrite some kind of return or call address, which allows hijacking of the +execution flow. + +The most trivial kinds of payloads is known as a \mintinline{ASM}{NOP} sled. Here the attacker appends as many \mintinline{ASM}{NOP} instructions before any -shellcode (e.g.\ to invoke \mintinline{shell}{/bin/sh}) and points the -overwritten \ac{ip} somewhere inside the \mintinline{ASM}{NOP}s. The execution -\enquote{slides} through the \mintinline{ASM}{NOP}s until it reaches the -shellcode. Most of the migration techniques described in this paper protect -against this kind of exploit but there are different and more complex ways of -exploiting \acp{bof} that are not that easily migrated. - -\subsection{Implications} +shell-code (e.g.\ to invoke \mintinline{shell}{/bin/sh}) and points the +overwritten \ac{ip} or function pointer somewhere inside the +\mintinline{ASM}{NOP}s. The execution \enquote{slides} (hence the name) through +the \mintinline{ASM}{NOP}s until it reaches the shell-code. Most of the +mitigation techniques described in this paper protect against this kind of +exploit but there are different and more complex ways of exploiting \acp{bof} +that are not that easily mitigated. \section{Concept and Methods}\label{ref:concept} -\subsection{Methods} +\subsection{Research Methods} -This paper describes several techniques that have been proposed to fix the -problems introduced by \acp{bof}. The performance impact, effectiveness (e.g.\ -did the technique actually prevent exploitation of \acp{bof}?) and how realistic -it is for developers to use the technique in real-world code (e.g.\ is -incremental introduction into an existing codebase possible). In the end, there -is a discussion about the current state. +This paper describes several techniques that have been proposed to mitigate the +problems introduced by \acp{bof} and tries to answer the following questions: -\subsection{Runtime Bounds Checks} +\begin{itemize} + + \item What is the performance impact? + + \item How effective is the technique? Did it actually prevent exploitation of + \acp{bof}? + + \item How realistic is it for developers to use the technique in real-world + code? Can it be introduced incrementally? + +\end{itemize} + +The paper focuses on solutions for the C language, since it is still the second +most used language as of December 2019~\cite{Tiobe2019}. Some of the described +techniques are language agnostic but this is not a focus of this paper. In the +end, there is a discussion about the current state. + +For the literature research, the paper~\citetitle{Detection2018} served as a +base. From there a snowball system search with combinations of the keywords +\enquote{buffer}, \enquote{overflow}, \enquote{detection}, \enquote{prevention} +and \enquote{dependent typing} was performed using +\url{https://scholar.google.com/}. + +Results are evaluated and prioritized using the following criteria: + +\begin{itemize} + + \item Type of publication in the following order: + + \begin{enumerate} + \item conference paper + \item unreleased paper + \item books + \item online sources + \end{enumerate} + + \item Number of citations + + \item Publisher + + \item Author's reputation and institute + + \item Overall quality (first by checking structure and abstract, then by + the actual content) + +\end{itemize} + + +\subsection{\Ac{rbc}} The easiest and maybe single most effective method to prevent \acp{bof} is to check, if a write or read operation is out of bounds. This requires storing the -size of a buffer together with the pointer to the buffer and check for each read -or write in the buffer, if it is in bounds at runtime. Still almost any language -that comes with a runtime, uses runtime checking. For this technique to be -effective effective in general, writes to a raw pointer must be disallowed. -Otherwise the security checks can be circumvented. +size of a buffer together with the pointer to the buffer (so called fat +pointers) and check for each read or write in the buffer, if it is in bounds at +runtime. Still almost any language that comes with a runtime, uses runtime +checking. For this technique to be effective effective in general, writes to a +raw pointer must be disallowed. Otherwise the security checks can be +circumvented. \Ac{rbc} introduces a runtime overhead for every indexed read or +write operation. This is a problem if a program runs on limited hardware or +might impact real-time properties. -\subsection{Prevent/Detect Overriding Return Address} +Introducing \ac{rbc} into an existing codebase is not easy. Using fat pointers +in a few functions does not prevent other parts of the code to use raw pointers +into the same buffer. So for this to be effective, the whole codebase needs to +be changed to disallow raw pointers, which, depending on the size, might not be +feasible. Still, if done correctly and consequently, it is simply impossible to +exploit \acp{bof} for code execution. \Ac{dos} is still possible because the +program terminates gracefully when a out of bounds index is used. -Since most traditional \ac{bof} exploits work by overriding the return address +\subsection{Prevent/Detect Overwriting Return Address} + +Since most traditional \ac{bof} exploits work by overwriting the return address in the current stack frame, preventing or at least detecting this, can be quite effective without much overhead at runtime. \citeauthor{Rad2001} describe a -technique that stores a redudnant copy of the return address in a secure memory +technique that stores a redundant copy of the return address in a secure memory area that is guarded by read-only memory, so it cannot be overwritten by overflows. When returning, the copy of the return address is compared to the one in the current stack frame and only, if it matches, the \mintinline{ASM}{RET} instruction is actually executed~\cite{Rad2001}. While this is effective against -\ac{rop} based exploits, it does not protect against vtable overrides. +stack based \acp{bof}, in the described form, it does not protect against vtable +overwrites. An extension could be made to also protect the \ac{plt} and vtables +but custom constructs using function pointers would still be vulnerable. Since +this technique is a compiler extension, no modification of the codebase is +required to enable it, and while it does not prevent all kinds of \ac{bof}, +mitigates all stack based \acp{bof} with only minimal overhead when calling and +returning from a function. -An older technique from 1998 proposes to put a canary word between the data of a -stack frame and the return address~\cite{Stackguard1998}. When returning, the -canary is checked, if it is still intact and if not, a \ac{bof} occurred. This -technique is used in major operating systems %TODO -but can be defeted, if there -is an information leak that leaks the cannary to the attacker. The attacker is -then able to construct a payload, that keeps the canary intact. +An older technique from 1998 proposes to put a canary word (named after the +canaries that were used in mines to detect low oxygen levels) between the data +of a stack frame and the return address~\cite{Stackguard1998}\cite{AtkDef2016}. +When returning, the canary is checked, if it is still intact and if not, a +\ac{bof} occurred. This technique is implemented by major +compilers~\cite{Gcc2003} but can be defeated, if there is an information leak +that leaks the canary to the attacker. The attacker is then able to construct a +payload, that keeps the canary intact. This mitigation has a minimal +performance impact~\cite{Gcc2003} and offers a good level of protection. It is a +compiler extension so no modification of the code base is needed. -\subsection{Restricting Language Features to a Secure Subset} -\subsection{Static Analysis} +% \subsection{Restricting Language Features to a Secure Subset} +% \subsection{Static Analysis} \subsection{Type System Solutions} \citeauthor{Dep2007} propose an extension to the C type system that extends it with dependent types. These types have an associated value, e.g.\ a pointer type -can have the buffer size associated to it. This prevents indexing into a buffer -with out-of-bounds values. This extension is a superset of C so any valid C code -can be compiled using the extension and the codebase is improved incrementally. -If the type extension is advanced enough, the additional information might form -the base for a formal verification. +can have the buffer size associated to it~\cite{Dep2007}. This prevents indexing +into a buffer with out-of-bounds values. This extension is a superset of C so +any valid C code can be compiled using the extension and the codebase is +improved incrementally. If the type extension is advanced enough, the +additional information might form the base for a formal verification. In some +cases, the type extensions can even be inferred~\cite{Dep2007}. + +This technique prevents all kinds of overflows, if used, but requires changes to +the codebase and is only effective where these changes are applied. Since it is +a compile-time solution, it does affect the compile-time but has no negative +effect on the runtime. \subsection{Address Space Layout Randomization} -\Ac{aslr} aims to prevent exploitatoin of \acp{bof} by placing code at random -locations in memory. That way, it is not trivial to set the return address to -point to the payload in memory. This is effective against generic exploits but -it is still posible to exploit \ac{bof} vulnerabilities in combination with -information leaks or other techniques like heap spraying. Also on 32 bit -systems, the address space is small enough to try a brute-force attempt until -the payload in memory is hit. +\Ac{aslr} aims to prevent exploitation of \acp{bof} by placing code at random +locations in memory~\cite{AtkDef2016}. That way, it is not trivial to set the +return address to point to the payload in memory. This is effective against +every kind of \ac{bof} vulnerability but it is still possible to exploit +\ac{bof} vulnerabilities in combination with information leaks or other +techniques like heap spraying. Also on 32 bit systems, the address space is +small enough to try a brute-force attempt until the payload in memory is +hit~\cite{Effectiveness2014}. + +This is another technique that works without modification of the code base. Also +there is no runtime overhead because nothing changed except the location of the +program. \subsection{w\^{}x Memory} -w\^{}x (also known as \ac{nx}) makes memory either writable or executable. That -way, an attacker cannot place arbitiary payloads in memory. There are still -techniques to exploit this by reusing existing executable code. The ret-to-libc -exploiting technique uses existing calls to the libc with attacker controlled -parameters, e.g.\ if the programm uses the \mintinline{shell}{system} command, -the attacker can plant \mintinline{shell}{/bin/sh} as parameter on the stack, -followed by the address of \mintinline{shell}{system} and get a shell on the -system. \ac{rop} (a superset of ret-to-libc exploits) uses so called \ac{rop} -gadgets, combinations of memory modifying instructions followed by the -\mintinline{ASM}{RET} instruction to build instruction chains, that execute the -desired shellcode. This is done by placing the desired return addresses in the -right order on the stack and reuses the existing code to circumvent the w\^{}x -protection. These combinations of memory modification followed by -\mintinline{ASM}{RET} instructions are called \ac{rop} chains and are turing -complete~\cite{Rop2007}, so in theory it is possible to implement any imaginable -payload, as long as the exploited program contains enough gadgets and the -overflowing buffer has enough space. +w\^{}x (also known as \ac{nx} or \ac{dep}) makes memory either writable or +executable~\cite{AtkDef2016}. That way, an attacker cannot place arbitrary +payloads in memory. There are still techniques to exploit this by reusing +existing executable code. The ret-to-libc exploiting technique uses existing +calls to the libc with attacker controlled parameters, e.g.\ if the program uses +the \mintinline{shell}{system} command, the attacker can plant +\mintinline{shell}{/bin/sh} as parameter on the stack, followed by the address +of \mintinline{shell}{system} and get a shell on the system. \ac{rop} (a +superset of ret-to-libc exploits) uses so called \ac{rop} gadgets, combinations +of memory modifying instructions followed by the \mintinline{ASM}{RET} +instruction to build instruction chains, that execute the desired shell-code. +This is done by placing the desired return addresses in the right order on the +stack and reuses the existing code to circumvent the w\^{}x protection. These +combinations of memory modification followed by \mintinline{ASM}{RET} +instructions are called \ac{rop} chains and are Turing complete~\cite{Rop2007}, +so in theory it is possible to implement any imaginable payload, as long as the +exploited program contains enough gadgets and the overflowing buffer has enough +space. \section{Discussion}\label{ref:discussion} -\subsection{Ineffective or Inefficient} +\subsection{Effectiveness} \subsubsection{\ac{aslr}} -\Ac{aslr} has been really effective and wildly used in production. It is +\Ac{aslr} has been proven effective and is wildly used in production. It is included in most major operating systems~\cite{FBSDaslr}. Some even use kernel \ac{aslr}~\cite{Linuxaslr}. Since this mechanism is active at runtime, it does -not require any changes in the code itself, the programm only has to be compiled +not require any changes in the code itself, the program only has to be compiled as a \ac{pie}. On 32-bit CPUs, only 16-bit of the address are randomized. These 16-bit can be brute forced in a few minutes or seconds~\cite{AslrEffective2004}. +There is no runtime overhead since the only change is the position of the +program in memory. Since there is no additional work except maybe recompilation, +this technique can and should be used on modern systems. + \subsubsection{w\^{}x} With the rise of \ac{rop} techniques, w\^{}x protection has been shown to be -ineffective. It makes vulnerabilities harder to exploit but does not prevent -anything. +ineffective. It makes vulnerabilities harder to exploit by preventing the most +naive types of payloads but it doesn't actually prevent exploits from happening. + +\Ac{nx} does not prevent any exploits but makes it harder for an attacker that +does not know the system, the program is running on (e.g.\ a network service). +It has no runtime overhead and is a compile-time option so it does not hurt to +enable \ac{nx}. \subsubsection{Runtime Bounds Checks} Checking for overflows at runtime is very effective but can have a huge performance impact so it is not feasible in every case. It also comes with other -footguns. There might be integer overflows when calculating the bounts which +footguns. There might be integer overflows when calculating the bounds which might introduce other problems. -Methods that have been shown to be ineffective (e.g.\ can be circumvented -easily) or inefficient (to much runtime overhead)\ldots - \subsection{State of the Art} -What techniques are currently used? +Operating systems started to compile C code to \ac{pie} by +default~\cite{ArchPie2017} and \ac{aslr} is enabled, too. Same goes for \ac{nx} +and stack canaries~\cite{ArchPie2017}. The combination of these mitigations +makes it hard to write general exploits for modern operating systems. -\subsection{Outlook} +To check the current state, the latest release of the \ac{gcc} (9.2) and the +latest commit of the LLVM-project (\mintinline[breaklines]{shell}{181ab91efc9}) +are compiled using the default configuration. The experiments are performed on a +64-bit Debian 9.11 system running on version 4.19.0 of the Linux kernel. The +following commands are used for compilation: +\begin{figure}[h!] +\begin{subfigure}[b]{.3\textwidth} +\begin{minted}{shell} + mkdir objdir \ + && cd objdir \ + && ../configure \ + --build=x86_64-linux-gnu \ + --host=x86_64-linux-gnu \ + --target=x86_64-linux-gnu \ + --disable-multilib \ + && make -j8 +\end{minted} +\caption{\ac{gcc} compilation script}\label{lst:gcc} +\end{subfigure} +\\ +\begin{subfigure}[b]{.3\textwidth} +\begin{minted}{shell} + mkdir build \ + && cd build \ + && cmake -DLLVM_ENABLE_PROJECTS=clang \ + -DCMAKE_BUILD_TYPE=Release \ + -G "Unix Makefiles" ../llvm + && make -j8 +\end{minted} +\caption{clang compilation script} +\end{subfigure} +\end{figure} + +The \mintinline{shell}{build}, \mintinline{shell}{host} and +\mintinline{shell}{target} parameters in~\ref{lst:gcc} only describe the target +platform for the compiler and \mintinline{shell}{disable-multilib} disables +32-bit support. The \mintinline{sh}{-j8} flag only tells make to use all 8 +available cores for compilation. + +The fresh builds of \ac{gcc} and clang compile the code from~\cref{lst:vuln} to +check which mitigations are enabled by default. Using +\mintinline[breaklines]{shell}{gcc -o vuln.gcc vuln.c} and +\mintinline[breaklines]{shell}{clang -o vuln.clang vuln.c} to compile the source +code, the \mintinline{shell}{checksec.sh} tool~\cite{Checksec2019} shows which +mitigations are active in the new binary: + +\begin{table}[h!] +\begin{center} +\begin{tabular}{lll} + \toprule + Mitigation & Active in \ac{gcc}? & Active in clang? \\ + \toprule + Stack Canary & No & No \\ + \midrule + \ac{nx} & Yes & Yes \\ + \midrule + \ac{pie} & No & No \\ + \bottomrule +\end{tabular} +\caption{Enabled mitigations in a default \ac{gcc} and clang + build}\label{tab:mitigations} +\end{center} +\end{table} + +Surprisingly enough, two of the most popular C compilers enable only one of the +described compile-time mitigations by default. Maintainer of operating system +packages of the compiler might choose a more secure configuration for the +compiler as shown in~\cite{ArchPie2017} but still, compiler vendors might want +to choose better defaults, too. + +So far, all described mitigations don't change anything about the existence of +\acp{bof} but just try to prevent the exploitation for code execution. The +vulnerable programs will still terminate if the stack canary is overwritten, a +call into \ac{nx} memory occurs or execution continues inside garbage data due +to \ac{aslr}. The underlying problem persists, only the worst results are +mitigated. \Ac{dos} is still a problem in safety critical systems (e.g.\ cars, +planes, medical devices) or in any area with real-time requirements. + +Language extensions to fix the problem of \acp{bof} as described +in~\cite{Dep2007} require lots of discipline to use them everywhere. They are +only useful if the whole codebase uses the new features. Introducing them in an +existing codebase is quite unrealistic since it requires lots of modifications. +On the other hand, this actually prevents \acp{bof} from happening and not just +from being exploited, so it looks like an interesting concept for safety +critical software. \section{Conclusion}\label{ref:conclusion} While there are many techniques, that protect against different types of -\acp{bof}, none of them is effctive in every situation. Maybe we've come to a +\acp{bof}, none of them is effective in every situation but in combination they +offer good protection against code execution attacks. Maybe we've come to a point where we have to stop using memory unsafe languages where it is not inevitable. There are many modern programming languages, that aim for the same -problem space as C, C++ or Fortran but without the issues comming/stemming %TODO -from these languages. If it is feasible to use a garbage collector, Go might -work just fine. If real-time properties are required, Rust could be the way to -go, without any language runtime and with deterministic memory management. For -any other problem, almost any other memory safe language is better than using -unsafe C. +problem space as C, C++ or Fortran but without the issues coming from these +languages. If it is feasible to use a garbage collector, languages like Go, Java +or even scripting languages like Python might work just fine. If real-time +properties are required, Rust could be the way to go, without any language +runtime and with deterministic memory management. For any other problem, almost +any other memory safe language is better than using unsafe C. -\section{Sources (Dummy Section for Deadline)} +% \section{Sources (Dummy Section for Deadline)} -\begin{itemize} +% \begin{itemize} - \item RAD:\ A Compile-Time Solution to Buffer Overflow Attacks~\cite{Rad2001} - (might not protect against e.g.\ vtable overrides, \ac{plt} address changes, - \dots) +% \item RAD:\ A Compile-Time Solution to Buffer Overflow Attacks~\cite{Rad2001} +% (might not protect against e.g.\ vtable overwrites, \ac{plt} address +% changes, \dots) - \item Dependent types for low-level programming~\cite{Dep2007} +% \item Dependent types for low-level programming~\cite{Dep2007} - \item StackGuard: Automatic Adaptive Detection and Prevention of - Buffer-Overflow Attachs~\cite{Stackguard1998} (ineffective in combination - with information leaks) +% \item StackGuard: Automatic Adaptive Detection and Prevention of +% Buffer-Overflow Attachs~\cite{Stackguard1998} (ineffective in combination +% with information leaks) - \item Type-Assisted Dynamic Buffer Overflow Detection~\cite{TypeAssisted2002} +% \item Type-Assisted Dynamic Buffer Overflow Detection~\cite{TypeAssisted2002} - \item On the Effectiveness of NX, SSP, RenewSSP, and \ac{aslr} against Stack - Buffer Overflows~\cite{Effectiveness2014} +% \item On the Effectiveness of NX, SSP, RenewSSP, and \ac{aslr} against Stack +% Buffer Overflows~\cite{Effectiveness2014} - \item What Do We Know About Buffer Overflow Detection?: A Survey on Techniques - to Detect A Persistent Vulnerability~\cite{Detection2018} +% \item What Do We Know About Buffer Overflow Detection?: A Survey on Techniques +% to Detect A Persistent Vulnerability~\cite{Detection2018} - \item Survey of Attacks and Defenses on Stack-based Buffer Overflow - Vulnerability~\cite{AtkDef2016} +% \item Survey of Attacks and Defenses on Stack-based Buffer Overflow +% Vulnerability~\cite{AtkDef2016} - \item Beyond stack smashing: recent advances in exploiting buffer - overruns~\cite{Smashing2004} +% \item Beyond stack smashing: recent advances in exploiting buffer +% overruns~\cite{Smashing2004} - \item Runtime countermeasures for code injection attacks against C and C++ - programs~\cite{Counter2012} +% \item Runtime countermeasures for code injection attacks against C and C++ +% programs~\cite{Counter2012} -\end{itemize} +% \end{itemize} \printbibliography{} diff --git a/work/acronyms.tex b/work/acronyms.tex index 495c2a9..ac10b83 100644 --- a/work/acronyms.tex +++ b/work/acronyms.tex @@ -52,3 +52,13 @@ short = DOS, long = denial of service } + +\DeclareAcronym{gcc}{ + short = GCC, + long = GNU compiler collection +} + +\DeclareAcronym{dep}{ + short = DEP, + long = data execution prevention +} diff --git a/work/bibliography.bib b/work/bibliography.bib index 88e9f16..8a15906 100644 --- a/work/bibliography.bib +++ b/work/bibliography.bib @@ -73,7 +73,7 @@ year = {2001} @ARTICLE{Smashing2004, author={{Pincus}, J. and {Baker}, B.}, - journal={{IEEE Security \& Privacy}}, + journal={{IEEE Security and Privacy (SP)}}, title={{Beyond stack smashing: recent advances in exploiting buffer overruns}}, year={2004}, @@ -126,6 +126,22 @@ year={2007} title = {{7.1.1-4: enable SSP and PIE by default}} } +@online{Heardbleed2014, + url = {http://heartbleed.com/}, + urlDate = {2019-12-15}, + year = {2014}, + title = {{The Heartbleed Bug}}, + author = {{Codenomicon}}, +} + +@online{Checksec2019, + url = {https://github.com/slimm609/checksec.sh}, + urlDate = {2019-12-16}, + year = {2019}, + title = {{Checksec.sh}}, + author = {{Klein}, Tobias} +} + @online{Tiobe2019, author = {{TIOBE}}, title = {{TIOBE Index for December 2019}},