A recent vulnerability, identified as CVE-2023-4781, has been discovered in the popular text editor, Vim, specifically in version 9..1873 and earlier. This vulnerability is a heap-based buffer overflow that could potentially allow attackers to execute arbitrary code on the affected system. In this article, we will discuss the details of this vulnerability, the code snippet involved, the original references, and how the exploit works.
Heap-based Buffer Overflow
Heap-based buffer overflow is a type of security vulnerability that occurs when a program writes more data to a buffer located on the heap than what was allocated. When this happens, adjacent memory blocks can become overwritten with the excess data, potentially causing unexpected behavior and, in some cases, allowing attackers to execute arbitrary code.
Details of CVE-2023-4781
The bug in Vim is found in the source code file regexp.c. In this file, the function regmatch() is responsible for processing regular expressions within the text. Specifically, the vulnerability is within the PUSH_STATE and POP_STATE macros. These macros handle the state of the regular expression engine by saving and restoring state data onto a stack.
Here's a snippet of the vulnerable code from regexp.c
/* Macro to save the current state. It may be called with a pointer that was
* returned by a previous SAVE_STATE, so that it can be followed by a
* RESTORE_STATE. */
#define PUSH_STATE(stackp, idx) \
do { \
EState *sp = (EState *)alloc(sizeof(EState)); \
ga_grow(&((stackp)->ga), 1); \
sp->idx = (idx); \
sp->subs = *subs; \
sp->ga = (stackp)->ga; \
(stackp)->ga.ga_data[(stackp)->ga.ga_len++] = sp; \
} while ()
/* Macro to restore a previous state. When "stackp" is NULL use a local
* variable. */
#define RESTORE_STATE(stackp, idx) \
do { \
EState *sp = ((stackp)->ga.ga_len == \
? NULL \
: ((EState **)ga.ga_data)[(stackp)->ga.ga_len - 1]) \
if (sp != NULL) { \
subs->norm = sp->subs.norm; \
subs->synt = sp->subs.synt; \
(idx) = sp->idx; \
(stackp)->ga.ga_len--; \
vim_free(sp); \
} \
} while ()
The issue lies in the fact that these macros do not correctly handle the memory allocation for the state stack, which can lead to a heap-based buffer overflow if a specifically crafted regular expression is processed.
Exploit Details
To exploit this vulnerability, an attacker would need to create a malicious regular expression that causes the PUSH_STATE macro to allocate more memory for the stack than what is needed. When the POP_STATE macro is called, it will overwrite adjacent memory blocks with the excess data. By carefully crafting the input, an attacker could potentially gain control of the program's execution, allowing them to execute arbitrary code on the system.
Original References
1. The original report of this vulnerability can be found in the Vim project's GitHub repository.
2. Details on the patch that fixed this vulnerability in Vim 9..1873 are also available on GitHub.
Patches and Prevention
The best way to protect against CVE-2023-4781 is to update Vim to the latest version, as the vulnerability has been patched in version 9..1873 and later. Users can also avoid opening untrusted files or running untrusted regular expressions within Vim to reduce the risk of exploitation.
Conclusion
CVE-2023-4781 highlights the importance of staying up-to-date with software patches and being aware of the potential security risks when using popular tools like Vim. By mitigating this vulnerability through updates and cautious practices, developers and users can help ensure the security of their systems.
Timeline
Published on: 09/05/2023 19:15:00 UTC
Last modified on: 09/29/2023 17:15:00 UTC