FreeRDP is a free implementation of the Remote Desktop Protocol. Prior to version 3.21.0, FastGlyph parsing trusts cbData/remaining length and never validates against the minimum size implied by cx/cy. A malicious server can trigger a client‑side global buffer overflow, causing a crash (DoS). Version 3.21.0 contains a patch for the issue.
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 |
|---|---|---|---|
| Freerdp | Freerdp | * | 3.21.0 (excluding) |
| Freerdp2 | Ubuntu | esm-apps/noble | * |
| Freerdp2 | Ubuntu | esm-infra/bionic | * |
| Freerdp2 | Ubuntu | esm-infra/focal | * |
| Freerdp2 | Ubuntu | jammy | * |
| Freerdp2 | Ubuntu | noble | * |
| Freerdp2 | Ubuntu | upstream | * |
| Freerdp3 | Ubuntu | noble | * |
| Freerdp3 | Ubuntu | questing | * |
| Freerdp3 | 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].
Related Attack Patterns
References
- https://github.com/FreeRDP/FreeRDP/blob/f96ee2a6dd02739325c2a4e36a14978b561f00ea/libfreerdp/cache/glyph.c#L463-L480
- https://github.com/FreeRDP/FreeRDP/blob/f96ee2a6dd02739325c2a4e36a14978b561f00ea/libfreerdp/codec/color.c#L261-L277
- https://github.com/FreeRDP/FreeRDP/blob/f96ee2a6dd02739325c2a4e36a14978b561f00ea/libfreerdp/core/graphics.c#L138
- https://github.com/FreeRDP/FreeRDP/blob/f96ee2a6dd02739325c2a4e36a14978b561f00ea/libfreerdp/core/orders.c#L2186C17-L2199
- https://github.com/FreeRDP/FreeRDP/releases/tag/3.21.0
- https://github.com/FreeRDP/FreeRDP/security/advisories/GHSA-7qxp-j2fj-c3pp
- https://github.com/FreeRDP/FreeRDP/security/advisories/GHSA-7qxp-j2fj-c3pp