# CVE-2026-33999: Xorg: xwayland: x.org x server: denial of service via integer underflow in xkb compatibility map handling

> An attacker with X11 access can trigger a buffer read overrun via integer underflow in XKB handling, causing denial of service.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 23 Apr 2026
- **Updated:** 15 Jul 2026
- **Also known as:** AZL-84630, AZL-84839, BELL-CVE-2026-33999, DEBIAN-CVE-2026-33999, ECHO-3bf6-384c-577f, GHSA-g562-3mh5-27v6, UBUNTU-CVE-2026-33999

## What is CVE-2026-33999?

CVE-2026-33999 is a high-severity vulnerability in Red Hat Enterprise Linux 10, published on 23 Apr 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

A flaw was found in the X.Org X server. This integer underflow vulnerability, specifically in the XKB compatibility map handling, allows an attacker with local or remote X11 server access to trigger a buffer read overrun. This can lead to memory-safety violations and potentially a denial of service (DoS) or other severe impacts.

Weakness: CWE-191 (Integer Underflow (Wrap or Wraparound))

## Which versions are affected by CVE-2026-33999?


## How do I fix CVE-2026-33999?

Apply the vendor's patch.

## Is CVE-2026-33999 being exploited?

There is no known exploitation of CVE-2026-33999 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-33999 and fix it if it is affected.

What it is: CVE-2026-33999 is a high-severity vulnerability in Red Hat Enterprise Linux 10, published on 23 Apr 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-33999 in the wild and no public exploit code.

Affected product: Red Hat Enterprise Linux 10. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-33999/ (Markdown: https://insights.sbomify.com/CVE-2026-33999/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-33999
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-33999
- OSV: https://osv.dev/vulnerability/CVE-2026-33999

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-33999/
Summaries are generated and may contain mistakes; the official description above is the record.