# CVE-2026-109088: libXtst infinite loop in RECORD EnableContext reply parsing

Source: https://junglewise.ai/threats/cve-2026-109088-a-malicious-x-server-could-send-malformed-record-enablecontext  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-10-27. Updated: 2026-10-27  
License: CC BY 4.0 with a link back

CVE-2026-109088 · Severity: medium · CVSS 6.5 · Published 2026-10-27

libXtst is an X Window System library used by applications to interact with the X server. A malicious X server can send specially crafted RECORD messages that cause X client applications to enter an infinite loop, effectively freezing and becoming unresponsive.

Vendors: [Freedesktop](https://junglewise.ai/threats/vendors/freedesktop).

## Quick answers

**Is CVE-2026-109088 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-109088 being exploited in the wild.

**How severe is CVE-2026-109088?** Medium severity, with a CVSS score of 6.5, published 27 October 2026.

**Which products and versions are affected?** Freedesktop libXtst before 1.2.6.

**Is there a fix for CVE-2026-109088?** Yes: fixed in libXtst 1.2.6. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-109088 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-109088?** Check whether you run Freedesktop libXtst 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.

## How to fix

- Fixed in libXtst 1.2.6

## Technical details

The parse_reply_call_callback function in libXtst versions before 1.2.6 fails to properly validate zero-progress RECORD reply elements from a malicious server. An attacker controlling an X server can send malformed EnableContext replies with either zero-length BIG-REQUESTS or undefined category bytes that cause the parsing loop to hang indefinitely. This results in a denial of service as the application remains locked in a busy loop.

## Affected products

- freedesktop libXtst before 1.2.6

## Timeline

- 2026-10-27: disclosed
- 2026-10-27: advisory

## References

- [https://gitlab.freedesktop.org/xorg/lib/libxtst/-/merge_requests/11](https://gitlab.freedesktop.org/xorg/lib/libxtst/-/merge_requests/11)

## Related threats

- [libXtst out-of-bounds read in RECORD reply parser](https://junglewise.ai/threats/cve-2026-94286-an-out-of-bounds-read-in-libxtst-s-record-reply-parser-in-libxtst)