# CVE-2026-23534: FreeRDP heap buffer overflow in ClearCodec bands decode path

Source: https://junglewise.ai/threats/cve-2026-23534-freerdp-heap-buffer-overflow-in-clearcodec-bands-decode-path  
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-2026-23534 · 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 security flaw in how the software processes image data could allow a malicious server to crash a user's connection or potentially take control of the user's computer. This risk is particularly high when connecting to untrusted or compromised remote servers.

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

## Quick answers

**Is CVE-2026-23534 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-23534 being exploited in the wild.

**How severe is CVE-2026-23534?** 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-2026-23534?** A patch was published on 2026-01-19: FreeRDP version 3.21.0 released Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-23534 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-23534?** 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_bands_data` function in `libfreerdp/codec/clear.c`. The vulnerability is triggered by insufficient validation of `xStart`, `xEnd`, `yStart`, and `yEnd` coordinates provided in a `WIRE_TO_SURFACE_PDU_1` stream. Specifically, the code checks if coordinates are greater than the destination bounds but fails to account for coordinates equal to the bounds, leading to an out-of-bounds write during the `FreeRDPWriteColor_int` operation. An attacker controlling a malicious RDP server can exploit this to cause a denial-of-service or achieve remote code execution on the client. The issue is resolved in version 3.21.0.

## Affected products

- FreeRDP FreeRDP < 3.21.0
- Red Hat Enterprise Linux 8, 9, 10

## Timeline

- 2026-01-19: advisory: GitHub Security Advisory and NVD entry published
- 2026-01-19: patched: FreeRDP version 3.21.0 released
- 2026-02-05: patched: Red Hat released security updates for RHEL 9

## 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/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-3frr-mp8w-4599](https://github.com/FreeRDP/FreeRDP/security/advisories/GHSA-3frr-mp8w-4599)
- [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)

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