# CVE-2026-23531: FreeRDP heap buffer overflow in ClearCodec

Source: https://junglewise.ai/threats/cve-2026-23531-freerdp-heap-buffer-overflow-in-clearcodec  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-01-19. Updated: 2026-06-30  
License: CC BY 4.0 with a link back

CVE-2026-23531 · Severity: critical · CVSS 9.8 · Published 2026-01-19

FreeRDP is an open-source tool used to connect to remote computers via the Remote Desktop Protocol. A vulnerability in how it handles certain image data allows a malicious server to crash the user's connection software or potentially take control of the user's computer. This could lead to a loss of service or the unauthorized access of sensitive data on the machine running the FreeRDP client.

Technologies: [FreeRDP](https://junglewise.ai/threats/technologies/freerdp). Vendors: [FreeRDP](https://junglewise.ai/threats/vendors/freerdp).

## Quick answers

**Is CVE-2026-23531 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-23531 being exploited in the wild.

**How severe is CVE-2026-23531?** Critical severity, with a CVSS score of 9.8, published 19 January 2026.

**Which products and versions are affected?** FreeRDP < 3.21.0.

**Is there a fix for CVE-2026-23531?** A patch was published on 2026-01-19: Version 3.21.0 released with fixes Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-23531 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-23531?** Check whether you run FreeRDP at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

A heap-based buffer overflow exists in FreeRDP's ClearCodec implementation within the `clear_decompress` function. When `glyphData` is present, the function calls `freerdp_image_copy_no_overlap` using destination rectangle coordinates (`destRect`) provided by the server without validating them against the target surface dimensions. An attacker controlling a malicious RDP server can send crafted RDPGFX surface updates with out-of-bounds coordinates to trigger an out-of-bounds read or write. This can result in a client-side crash (DoS) or heap corruption, potentially leading to arbitrary code execution. The issue is fixed in version 3.21.0 by implementing proper bounds checking for destination rectangles.

## Affected products

- FreeRDP FreeRDP < 3.21.0

## Timeline

- 2026-01-19: advisory: GitHub Security Advisory GHSA-xj5h-9cr5-23c5 published
- 2026-01-19: patched: Version 3.21.0 released with fixes

## References

- [https://github.com/FreeRDP/FreeRDP/blob/38514dfa5813aa945a86cfbcec279033f8394468/libfreerdp/codec/clear.c](https://github.com/FreeRDP/FreeRDP/blob/38514dfa5813aa945a86cfbcec279033f8394468/libfreerdp/codec/clear.c)
- [https://github.com/FreeRDP/FreeRDP/releases/tag/3.21.0](https://github.com/FreeRDP/FreeRDP/releases/tag/3.21.0)
- [https://github.com/FreeRDP/FreeRDP/security/advisories/GHSA-xj5h-9cr5-23c5](https://github.com/FreeRDP/FreeRDP/security/advisories/GHSA-xj5h-9cr5-23c5)
- [https://access.redhat.com/errata/RHSA-2026:2048](https://access.redhat.com/errata/RHSA-2026:2048)
- [https://access.redhat.com/errata/RHSA-2026:2081](https://access.redhat.com/errata/RHSA-2026:2081)
- [https://access.redhat.com/errata/RHSA-2026:2222](https://access.redhat.com/errata/RHSA-2026:2222)
- [https://access.redhat.com/errata/RHSA-2026:2714](https://access.redhat.com/errata/RHSA-2026:2714)

## Related threats

- [FreeRDP heap use-after-free in brush cache](https://junglewise.ai/threats/cve-2026-125394-freerdp-before-3-33-0-contains-a-heap-use-after-free)
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- [FreeRDP denial of service in NLA shadow server via malformed TSRequest](https://junglewise.ai/threats/cve-2026-121960-freerdp-before-3-32-2-contains-a-denial-of-service-vulnerability)
- [FreeRDP heap out-of-bounds write in RDPGFX HashTable_GetKeys](https://junglewise.ai/threats/cve-2026-121958-freerdp-through-3-32-1-has-a-heap-out-of-bounds-write-in-the)