CVE-2026-55999 xorg-server / xwayland glamor font atlas Heap Buffer Overflow
High 8.5
Published
Updated
Check this codebase for CVE-2026-55999 and fix it if it is affected.
What it is: CVE-2026-55999 is a high-severity memory corruption vulnerability in X.org X Server, published on 8 Jul 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-55999 in the wild and no public exploit code.
Affected product: X.org X Server. 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-2026-55999/ (Markdown: https://insights.sbomify.com/CVE-2026-55999/index.md)
Local attackers can trigger a heap buffer overflow in the X server via malicious PCX fonts, potentially leading to code execution or privilege escalation.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-55999?
CVE-2026-55999 is a high-severity memory corruption vulnerability in X.org X Server, published on 8 Jul 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Official description
Local attackers with a X connection able to provide PCX fonts to the X server xorg-server before 21.2.24 and xwayland before 24.1.13 could cause a heap buffer overflow via SetFont due to missing glyph boundary checks.
Weakness: CWE-122
Which versions are affected by CVE-2026-55999?
It affects 2 products.
Linux distribution packages (40)
xorg-x11-server-Xdmx AlmaLinux:8 | All versions | 1.20.11-28.el8_10.3 |
xorg-x11-server-Xephyr AlmaLinux:8 | All versions | 1.20.11-28.el8_10.3 |
xorg-x11-server-Xnest AlmaLinux:8 | All versions | 1.20.11-28.el8_10.3 |
xorg-x11-server-Xorg AlmaLinux:8 | All versions | 1.20.11-28.el8_10.3 |
xorg-x11-server-Xvfb AlmaLinux:8 | All versions | 1.20.11-28.el8_10.3 |
xorg-x11-server-Xwayland AlmaLinux:8 | All versions | 21.1.3-20.el8_10.3 |
xorg-x11-server-common AlmaLinux:8 | All versions | 1.20.11-28.el8_10.3 |
xorg-x11-server-devel AlmaLinux:8 | All versions | 1.20.11-28.el8_10.3 |
xorg-x11-server-source AlmaLinux:8 | All versions | 1.20.11-28.el8_10.3 |
xorg-x11-server-Xdmx AlmaLinux:9 | All versions | 1.20.11-34.el9_8.3 |
xorg-x11-server-Xephyr AlmaLinux:9 | All versions | 1.20.11-34.el9_8.3 |
xorg-x11-server-Xnest AlmaLinux:9 | All versions | 1.20.11-34.el9_8.3 |
xorg-x11-server-Xorg AlmaLinux:9 | All versions | 1.20.11-34.el9_8.3 |
xorg-x11-server-Xvfb AlmaLinux:9 | All versions | 1.20.11-34.el9_8.3 |
xorg-x11-server-common AlmaLinux:9 | All versions | 1.20.11-34.el9_8.3 |
xorg-x11-server-devel AlmaLinux:9 | All versions | 1.20.11-34.el9_8.3 |
xorg-x11-server-source AlmaLinux:9 | All versions | 1.20.11-34.el9_8.3 |
xorg-x11-server Red Hat:enterprise_linux:8::appstream | All versions | 0:1.20.11-28.el8_10.3 |
xorg-x11-server-Xdmx Red Hat:enterprise_linux:8::appstream | All versions | 0:1.20.11-28.el8_10.3 |
xorg-x11-server-Xdmx-debuginfo Red Hat:enterprise_linux:8::appstream | All versions | 0:1.20.11-28.el8_10.3 |
xorg-x11-server-Xephyr Red Hat:enterprise_linux:8::appstream | All versions | 0:1.20.11-28.el8_10.3 |
xorg-x11-server-Xephyr-debuginfo Red Hat:enterprise_linux:8::appstream | All versions | 0:1.20.11-28.el8_10.3 |
xorg-x11-server-Xnest Red Hat:enterprise_linux:8::appstream | All versions | 0:1.20.11-28.el8_10.3 |
xorg-x11-server-Xnest-debuginfo Red Hat:enterprise_linux:8::appstream | All versions | 0:1.20.11-28.el8_10.3 |
xorg-x11-server-Xorg Red Hat:enterprise_linux:8::appstream | All versions | 0:1.20.11-28.el8_10.3 |
xorg-x11-server-Xorg-debuginfo Red Hat:enterprise_linux:8::appstream | All versions | 0:1.20.11-28.el8_10.3 |
xorg-x11-server-Xvfb Red Hat:enterprise_linux:8::appstream | All versions | 0:1.20.11-28.el8_10.3 |
xorg-x11-server-Xvfb-debuginfo Red Hat:enterprise_linux:8::appstream | All versions | 0:1.20.11-28.el8_10.3 |
xorg-x11-server-Xwayland Red Hat:enterprise_linux:8::appstream | All versions | 0:21.1.3-20.el8_10.3 |
xorg-x11-server-Xwayland-debuginfo Red Hat:enterprise_linux:8::appstream | All versions | 0:21.1.3-20.el8_10.3 |
xorg-x11-server-Xwayland-debugsource Red Hat:enterprise_linux:8::appstream | All versions | 0:21.1.3-20.el8_10.3 |
xorg-x11-server-common Red Hat:enterprise_linux:8::appstream | All versions | 0:1.20.11-28.el8_10.3 |
xorg-x11-server-debuginfo Red Hat:enterprise_linux:8::appstream | All versions | 0:1.20.11-28.el8_10.3 |
xorg-x11-server-debugsource Red Hat:enterprise_linux:8::appstream | All versions | 0:1.20.11-28.el8_10.3 |
xorg-x11-server-Xdmx-debuginfo Red Hat:enterprise_linux:8::crb | All versions | 0:1.20.11-28.el8_10.3 |
xorg-x11-server-Xephyr-debuginfo Red Hat:enterprise_linux:8::crb | All versions | 0:1.20.11-28.el8_10.3 |
xorg-x11-server-Xnest-debuginfo Red Hat:enterprise_linux:8::crb | All versions | 0:1.20.11-28.el8_10.3 |
xorg-x11-server-Xorg-debuginfo Red Hat:enterprise_linux:8::crb | All versions | 0:1.20.11-28.el8_10.3 |
xorg-x11-server-Xvfb-debuginfo Red Hat:enterprise_linux:8::crb | All versions | 0:1.20.11-28.el8_10.3 |
xorg-x11-server-debuginfo Red Hat:enterprise_linux:8::crb | All versions | 0:1.20.11-28.el8_10.3 |
Products include X.org X Server, X.org Xwayland.
How do I fix CVE-2026-55999?
Apply the vendor's patch.
Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.
Is CVE-2026-55999 being exploited?
There is no known exploitation of CVE-2026-55999 in the wild and no public exploit code.
Other vulnerabilities in X.org X Server
Sources
Also known as ALSA-2026:38486, ALSA-2026:38487, ALSA-2026:38488, AZL-92196, BELL-CVE-2026-55999, CLSA-2026-1784295645 and 24 more.