xbuf_format_converter, used as part of exif_read_data, was appending a terminating null character to the generated string, but was not using its standard append char function. As a result, if the buffer was full, it would result in an out-of-bounds write. This issue affects HHVM versions prior to 4.56.3, all versions between 4.57.0 and 4.80.1, all versions between 4.81.0 and 4.93.1, and versions 4.94.0, 4.95.0, 4.96.0, 4.97.0, 4.98.0.
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 |
| Hhvm |
Facebook |
* |
4.56.3 (excluding) |
| Hhvm |
Facebook |
4.57.0 (including) |
4.80.2 (excluding) |
| Hhvm |
Facebook |
4.81.0 (including) |
4.93.2 (excluding) |
| Hhvm |
Facebook |
4.94.0 (including) |
4.94.0 (including) |
| Hhvm |
Facebook |
4.95.0 (including) |
4.95.0 (including) |
| Hhvm |
Facebook |
4.96.0 (including) |
4.96.0 (including) |
| Hhvm |
Facebook |
4.97.0 (including) |
4.97.0 (including) |
| Hhvm |
Facebook |
4.98.0 (including) |
4.98.0 (including) |
| Hhvm |
Ubuntu |
bionic |
* |
| Hhvm |
Ubuntu |
trusty |
* |
| Hhvm |
Ubuntu |
xenial |
* |
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