# CVE-2026-23533: FreeRDP heap buffer overflow in ClearCodec decode path

Source: https://junglewise.ai/threats/cve-2026-23533-freerdp-heap-buffer-overflow-in-clearcodec-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-2026-23533 · 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 allows a malicious server to attack a user's computer when they attempt to connect. This could result in the application crashing or, in more severe cases, allow the attacker to run unauthorized code on the user's system.

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

## Quick answers

**Is CVE-2026-23533 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-23533 being exploited in the wild.

**How severe is CVE-2026-23533?** 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-2026-23533?** A patch was published on 2026-01-19: Fixed in version 3.21.0 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-23533 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-23533?** 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_residual_data` function. The vulnerability is rooted in `clear_resize_buffer`, where an integer overflow during size calculation leads to an undersized memory allocation. When processing `WIRE_TO_SURFACE_PDU_1` messages, a malicious server can provide crafted width, height, and residual data to trigger out-of-bounds writes. This can lead to a denial of service (crash) or potential remote code execution on the client machine. The issue is fixed in version 3.21.0.

## Affected products

- FreeRDP FreeRDP < 3.21.0
- Red Hat Enterprise Linux 7, 8, 9, 10

## Timeline

- 2026-01-19: disclosed
- 2026-01-19: patched: Fixed in version 3.21.0
- 2026-02-05: advisory: Red Hat security advisory issued

## 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-32q9-m5qr-9j2v](https://github.com/FreeRDP/FreeRDP/security/advisories/GHSA-32q9-m5qr-9j2v)
- [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)

## 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)
- [FreeRDP heap buffer overflow in RD Gateway RPC client](https://junglewise.ai/threats/cve-2026-121964-freerdp-before-3-32-2-contains-a-heap-based-buffer-overflow-in)
- [FreeRDP use-after-free in dynamic rdpsnd channel](https://junglewise.ai/threats/cve-2026-121963-freerdp-before-3-32-2-contains-a-use-after-free-vulnerability-in)
- [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)