CVE-2026-22858: freerdp Out-of-bounds Read

Vulnerability summary

CVE-2026-22858 is a critical (CVSS 9.1) Out-of-bounds Read vulnerability in freerdp. EPSS estimates a 0.70% chance of exploitation in the next 30 days, higher than 52.4% of scored vulnerabilities. 1 public exploit is recorded.

Timeline

1. 14-01-2026
   PublishedVulnerability first disclosed.
2. 19-08-2026
   Last modifiedVulnerability information updated.

Description

FreeRDP is a free implementation of the Remote Desktop Protocol. Prior to 3.20.1, global-buffer-overflow was observed in FreeRDP's Base64 decoding path. The root cause appears to be implementation-defined char signedness: on Arm/AArch64 builds, plain char is treated as unsigned, so the guard c <= 0 can be optimized into a simple c != 0 check. As a result, non-ASCII bytes (e.g., 0x80-0xFF) may bypass the intended range restriction and be used as an index into a global lookup table, causing out-of-bounds access. This vulnerability is fixed in 3.20.1.

• CWE-125Out-of-bounds ReadThe product reads data past the end, or before the beginning, of the intended buffer.
• CWE-758Reliance on Undefined, Unspecified, or Implementation-Defined BehaviorThe product uses an API function, data structure, or other entity in a way that relies on properties that are not always guaranteed to hold for that entity.
• CWE-787Out-of-bounds WriteThe product writes data past the end, or before the beginning, of the intended buffer.