Vim is an open source, command line text editor. Patch v9.1.0038 optimized how the cursor position is calculated and removed a loop, that verified that the cursor position always points inside a line and does not become invalid by pointing beyond the end of
a line. Back then we assumed this loop is unnecessary. However, this change made it possible that the cursor position stays invalid and points beyond the end of a line, which would eventually cause a heap-buffer-overflow when trying to access the line pointer at
the specified cursor position. Its not quite clear yet, what can lead to this situation that the cursor points to an invalid position. Thats why patch v9.1.0707 does not include a test case. The only observed impact has been a program crash. This issue has been addressed in with the patch v9.1.0707. All users are advised to upgrade.
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 |
Vim |
9.1.0038 (including) |
9.1.0707 (excluding) |
| 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