# CVE-2026-44950: fs_read_glyphs() heap buffer overflow via cumulative glyph data overflow in libXfont2

> A malicious font server can trigger a heap buffer overflow in libXfont2 via cumulative glyph data, potentially allowing arbitrary code execution.

- **Severity:** Critical 9.5 (`CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 10 Sep 2026
- **Updated:** 10 Sep 2026
- **Also known as:** AZL-101733, DEBIAN-CVE-2026-44950, GHSA-72vv-3gwg-8289, UBUNTU-CVE-2026-44950

## What is CVE-2026-44950?

CVE-2026-44950 is a critical memory corruption vulnerability in Container suse/kiosk/tigervnc-x11vnc:1.14-63.8, published on 10 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

fs_read_glyphs() in the libXfont2 font-server client (src/fc/fserve.c) copies each glyph's bitmap into a single buffer. Existing checks validates only that the source slice (position, length) lies within the source bitmap buffer. It does not check whether the running destination cursor has exceeded the allocation.

A malicious font server can send overlapping source offsets -- for example 1000 glyphs each referencing {position:0, length:64} with nbytes=64. Each individual source range passes the existing validation, but the cumulative writes total 64000 bytes into a 64-byte destination buffer. This is a heap buffer overflow with attacker-controlled content.

Weakness: CWE-122 (Heap-based Buffer Overflow)

## Which versions are affected by CVE-2026-44950?


## How do I fix CVE-2026-44950?

Apply the vendor's patch.

## Is CVE-2026-44950 being exploited?

There is no known exploitation of CVE-2026-44950 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-44950 and fix it if it is affected.

What it is: CVE-2026-44950 is a critical memory corruption vulnerability in Container suse/kiosk/tigervnc-x11vnc:1.14-63.8, published on 10 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-44950 in the wild and no public exploit code.

Affected product: Container suse/kiosk/tigervnc-x11vnc:1.14-63.8. 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-2026-44950/ (Markdown: https://insights.sbomify.com/CVE-2026-44950/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-44950
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-44950
- OSV: https://osv.dev/vulnerability/CVE-2026-44950

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-44950/
Summaries are generated and may contain mistakes; the official description above is the record.