CVE-2026-55192
Description
A flaw was found in FreeRDP. A malicious Remote Desktop Protocol (RDP) server can provide a specially crafted H.264 video stream that causes the client's H.264 decoder to read beyond its allocated memory. This out-of-bounds read can lead to the disclosure of sensitive client memory or cause the client application to crash, resulting in a denial of service.
Statement
An out-of-bounds memory read flaw was found in FreeRDP's H.264 video decoder (libfreerdp/codec/h264.c). When handling AVC420 or AVC444 bitstreams, decoder backends fail to validate frame dimensions against negotiated RDPGFX surface boundaries. A malicious RDP server can send a video frame smaller than the surface, causing yuv420_context_decode and YUV-to-RGB conversion paths to read past allocated memory buffers. This allows an untrusted server to exfiltrate sensitive client memory contents or crash the client application.
Mitigation
To mitigate this vulnerability, disable H.264 graphics acceleration in client connection parameters (e.g., omitting `/gfx:avc420` or `/gfx:avc444` in `xfreerdp`) to force legacy RemoteFX or standard software bitmap rendering.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
The following CVSS metrics and score provided are preliminary and subject to review.
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 8.1 | N/A | N/A |
| Attack Vector | Network | N/A | N/A |
| Attack Complexity | Low | N/A | N/A |
| Privileges Required | None | N/A | N/A |
| User Interaction | Required | N/A | N/A |
| Scope | Unchanged | N/A | N/A |
| Confidentiality | High | N/A | N/A |
| Integrity Impact | None | N/A | N/A |
| Availability Impact | High | N/A | N/A |
Vector
Red Hat: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:H
Understanding the Weakness (CWE)
Confidentiality
Technical Impact: Read Memory
An attacker could get secret values such as cryptographic keys, PII, memory addresses, or other information that could be used in additional attacks.
Confidentiality
Technical Impact: Bypass Protection Mechanism
Out-of-bounds memory could contain memory addresses or other information that can be used to bypass ASLR and other protection mechanisms in order to improve the reliability of exploiting a separate weakness for code execution.
Availability
Technical Impact: DoS: Crash, Exit, or Restart
An attacker could cause a segmentation fault or crash by causing memory to be read outside of the bounds of the buffer. This is especially likely when the code reads a variable amount of data and assumes that a sentinel exists to stop the read operation, such as a NUL in a string.
Other
Technical Impact: Varies by Context
The read operation could produce other undefined or unexpected results.
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