CVE-2026-29774
Published: 13 March 2026
Summary
CVE-2026-29774 is a medium-severity Out-of-bounds Write (CWE-787) vulnerability in Freerdp Freerdp. Its CVSS base score is 5.3 (Medium).
Operationally, exploitation aligns with the MITRE ATT&CK technique Exploitation for Client Execution (T1203); ranked at the 23.9th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.
The strongest mitigations our analysis identified are NIST 800-53 SI-10 (Information Input Validation) and SI-2 (Flaw Remediation).
Deeper analysis
CVE-2026-29774 is a client-side heap buffer overflow vulnerability in FreeRDP, a free implementation of the Remote Desktop Protocol. The issue affects FreeRDP versions prior to 3.24.0 and occurs in the client's AVC420/AVC444 YUV-to-RGB conversion path within yuv.c. Specifically, the clamp() function at line 347 validates only the top/bottom coordinates of H.264 metablock regionRects against the surface or YUV height, but lacks horizontal bounds checks for left/right against the surface width. This allows unchecked pointer arithmetic in avc420_yuv_to_rgb at line 67, where destination pointers are computed using rect->left, potentially writing far beyond the allocated heap buffer.
A remote attacker controlling an RDP server can exploit this vulnerability by sending a malicious WIRE_TO_SURFACE_PDU_1 with the AVC420 codec, including a regionRects entry where the left coordinate greatly exceeds the surface width, such as left=60000 on a 128px surface. Any unauthenticated FreeRDP client connecting to the server will decode the H.264 bitstream successfully, but yuv420_process_work_callback will invoke avc420_yuv_to_rgb, resulting in pointer arithmetic that writes 16-byte SSE vectors over 1888 bytes past the heap allocation, such as pDstPoint = pDstData + rect->top * nDstStep + rect->left * 4. This leads to heap corruption with limited availability impact, rated at CVSS 5.3 (AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L) and mapped to CWE-787 (Out-of-bounds Write).
The vulnerability is addressed in FreeRDP 3.24.0, as detailed in the project's GitHub security advisory GHSA-5q35-hv9x-7794 and the fixing commit 6482b7a92fff3959582cef052d1967ad6bde3738, which presumably adds the missing left/right bounds validation. Security practitioners should ensure FreeRDP clients are updated to 3.24.0 or later to mitigate this issue.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-12055
Vulnerability details
FreeRDP is a free implementation of the Remote Desktop Protocol. Prior to 3.24.0, a client-side heap buffer overflow occurs in the FreeRDP client's AVC420/AVC444 YUV-to-RGB conversion path due to missing horizontal bounds validation of H.264 metablock regionRects coordinates. In yuv.c,…
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the clamp() function (line 347) only validates top/bottom against the surface/YUV height, but never checks left/right against the surface width. When avc420_yuv_to_rgb (line 67) computes destination and source pointers using rect->left, it performs unchecked pointer arithmetic that can reach far beyond the allocated surface buffer. A malicious server sends a WIRE_TO_SURFACE_PDU_1 with AVC420 codec containing a regionRects entry where left greatly exceeds the surface width (e.g., left=60000 on a 128px surface). The H.264 bitstream decodes successfully, then yuv420_process_work_callback calls avc420_yuv_to_rgb which computes pDstPoint = pDstData + rect->top * nDstStep + rect->left * 4, writing 16-byte SSE vectors 1888+ bytes past the allocated heap region. This vulnerability is fixed in 3.24.0.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
Client-side heap buffer overflow in FreeRDP RDP client is directly triggered by a malicious server sending crafted AVC420/AVC444 H.264 data over RDP, enabling remote exploitation of the client application upon connection.
CVEs Like This One
Affected Assets
Mitigating Controls
Mitigating Controls (NIST 800-53 r5) AI
Directly requires timely application of the vendor patch (FreeRDP 3.24.0) that adds the missing left/right bounds checks in yuv.c.
Mandates validation of untrusted input (regionRects left/right coordinates from WIRE_TO_SURFACE_PDU_1) before pointer arithmetic in avc420_yuv_to_rgb.
Requires memory-protection mechanisms that can block or contain the out-of-bounds write that produces the heap corruption.