# CVE-2026-34085: Memory corruption in fontconfig

> An off-by-one error in fontconfig allows attackers to trigger a one-byte out-of-bounds write, potentially leading to code execution or crashes.

- **Severity:** Medium 5.9 (`CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 25 Mar 2026
- **Updated:** 2 Apr 2026
- **Also known as:** GHSA-jxv8-p782-98cx, JLSEC-2026-79, RHSA-2026:13722

## What is CVE-2026-34085?

CVE-2026-34085 is a medium-severity memory corruption vulnerability in fontconfig, published on 25 Mar 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

fontconfig before 2.17.1 has an off-by-one error in allocation during sfnt capability handling, leading to a one-byte out-of-bounds write, and potentially a crash or code execution. This is in FcFontCapabilities in fcfreetype.c.

Weakness: CWE-193 (Off-by-one Error)

## Which versions are affected by CVE-2026-34085?

It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `fontconfig` | Red Hat:hummingbird:1 | All versions | 0:2.17.1-0.1.hum1 |
| `fontconfig-devel` | Red Hat:hummingbird:1 | All versions | 0:2.17.1-0.1.hum1 |
| `fontconfig-devel-doc` | Red Hat:hummingbird:1 | All versions | 0:2.17.1-0.1.hum1 |

Products: Fontconfig Project Fontconfig.

## How do I fix CVE-2026-34085?

Upgrade to a fixed version.

## Is CVE-2026-34085 being exploited?

There is no known exploitation of CVE-2026-34085 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-34085 and fix it if it is affected.

What it is: CVE-2026-34085 is a medium-severity memory corruption vulnerability in fontconfig, published on 25 Mar 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-2026-34085 in the wild and no public exploit code.

Affected product: fontconfig. 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-2026-34085/ (Markdown: https://insights.sbomify.com/CVE-2026-34085/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-34085
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-34085
- OSV: https://osv.dev/vulnerability/CVE-2026-34085

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-34085/
Summaries are generated and may contain mistakes; the official description above is the record.