# CVE-2026-93543: libXi out-of-bounds read in XI2 class parser

Source: https://junglewise.ai/threats/cve-2026-93543-an-out-of-bounds-read-in-libxi-s-xi2-class-parser-in-libxi-before  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-24. Updated: 2026-09-26  
License: CC BY 4.0 with a link back

CVE-2026-93543 · Severity: high · CVSS 7.4 · Published 2026-09-24

libXi is a library that allows X11 client applications to communicate with input devices through the X server. A malicious or compromised X server can send specially crafted messages that trigger an out-of-bounds read in libXi's XI2 class parser, crashing any connected X client application that uses this functionality.

Technologies: [X.Org libXi](https://junglewise.ai/threats/technologies/libxi). Vendors: [X.Org](https://junglewise.ai/threats/vendors/x-org).

## Quick answers

**Is CVE-2026-93543 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-93543 being exploited in the wild.

**How severe is CVE-2026-93543?** High severity, with a CVSS score of 7.4, published 24 September 2026.

**Which products and versions are affected?** X.Org libXi before 1.8.4.

**Is there a fix for CVE-2026-93543?** A patch was published on 2026-09-23. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-93543 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-93543?** Check whether you run X.Org libXi 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

The vulnerability is an out-of-bounds read in the XI2 class parser within libXi before version 1.8.4, occurring during parsing of class records in X server replies. The flaw is triggered when a malicious X server sends crafted XIQueryDevice or similar XI2 protocol messages with invalid class payloads, allowing the server to read memory beyond buffer boundaries. The fix adds proper payload validation via a validate_class_payload() function to ensure declared wire lengths match actual data requirements.

## Affected products

- X.Org libXi before 1.8.4

## Timeline

- 2026-09-24: disclosed
- 2026-09-23: patched

## References

- [https://gitlab.freedesktop.org/xorg/lib/libxi/-/merge_requests/23/diffs?commit_id=e2089ab748828273f916bbffd4e65b506aa50fdc](https://gitlab.freedesktop.org/xorg/lib/libxi/-/merge_requests/23/diffs?commit_id=e2089ab748828273f916bbffd4e65b506aa50fdc)

## Related threats

- [libXi heap overflow in DEVICE_ENABLE reply handling](https://junglewise.ai/threats/cve-2026-109090-a-malicious-x-server-could-cause-a-heap-overflow-by-injecting-a)
- [libXi heap buffer overflow in DEVICE_RESOLUTION handling](https://junglewise.ai/threats/cve-2026-109089-a-buffer-overflow-when-handling-device-resolution-in-libxi)
- [libXi out-of-bounds read in XListInputDevices() class parsing](https://junglewise.ai/threats/cve-2026-94281-an-out-of-bounds-read-in-libxi-s-xlistinputdevices-class-parsing)
- [libXi out-of-bounds read in XI2 XIQueryDevice reply parsing](https://junglewise.ai/threats/cve-2026-93544-an-out-of-bounds-read-in-libxi-s-xi2-xiquerydevice-reply-parsing)
- [libXi out-of-bounds read in XI2 class parsing](https://junglewise.ai/threats/cve-2026-93542-an-out-of-bounds-read-in-libxi-s-xi2-class-parsing-via-size)