Vim is an open source command line text editor. When performing a search and displaying the search-count message is disabled (:set shm+=S), the search pattern is displayed at the bottom of the screen in a buffer (msgbuf). When right-left mode (:set rl) is enabled, the search pattern is reversed. This happens by allocating a new buffer. If the search pattern contains some ASCII NUL characters, the buffer allocated will be smaller than the original allocated buffer (because for allocating the reversed buffer, the strlen() function is called, which only counts until it notices an ASCII NUL byte ) and thus the original length indicator is wrong. This causes an overflow when accessing characters inside the msgbuf by the previously (now wrong) length of the msgbuf. The issue has been fixed as of Vim patch v9.1.0689.
Weakness
A heap overflow condition is a buffer overflow, where the buffer that can be overwritten is allocated in the heap portion of memory, generally meaning that the buffer was allocated using a routine such as malloc().
Affected Software
| Name |
Vendor |
Start Version |
End Version |
| Vim |
Ubuntu |
devel |
* |
| Vim |
Ubuntu |
upstream |
* |
Potential Mitigations
- Use automatic buffer overflow detection mechanisms that are offered by certain compilers or compiler extensions. Examples include: the Microsoft Visual Studio /GS flag, Fedora/Red Hat FORTIFY_SOURCE GCC flag, StackGuard, and ProPolice, which provide various mechanisms including canary-based detection and range/index checking.
- D3-SFCV (Stack Frame Canary Validation) from D3FEND [REF-1334] discusses canary-based detection in detail.
- Run or compile the software using features or extensions that randomly arrange the positions of a program’s executable and libraries in memory. Because this makes the addresses unpredictable, it can prevent an attacker from reliably jumping to exploitable code.
- Examples include Address Space Layout Randomization (ASLR) [REF-58] [REF-60] and Position-Independent Executables (PIE) [REF-64]. Imported modules may be similarly realigned if their default memory addresses conflict with other modules, in a process known as “rebasing” (for Windows) and “prelinking” (for Linux) [REF-1332] using randomly generated addresses. ASLR for libraries cannot be used in conjunction with prelink since it would require relocating the libraries at run-time, defeating the whole purpose of prelinking.
- For more information on these techniques see D3-SAOR (Segment Address Offset Randomization) from D3FEND [REF-1335].
References