CVE-2026-34085: fontconfig before 2.17.1 has an off-by-one error in allocation during sfnt capability handling, leading to a o

Routine

MEDIUM 5.9DOWNGRADE

CVE-2026-34085 is a medium-severity flaw (CVSS 5.9) affecting fontconfig. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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.

Why this priority

No elevated risk signals yet

No fix is published yet: follow the downgrade or mitigation steps.

Risk facts

CVSS score	5.9 (Medium)
Attack vector	Local
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.1% (top 97%)
CISA exploited list	No
Weakness	CWE-193
Published	2026-03-25
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: fontconfig project

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-03-25 17:17 UTCPublished CVE record published
2026-06-17 10:38 UTCUpdated Record last modified

fontconfig project fontconfig DOWNGRADE

Affected: 2.17.0

Fixed in: no fixed release known

Safe to downgrade to: a release before 2.17.0

1. Check installed version

apt-cache policy fontconfig || rpm -q fontconfig || fontconfig --version

2. No fixed release: DOWNGRADE to a release before 2.17.0 (Debian / Ubuntu)

apt-cache madison fontconfig sudo apt install fontconfig=<VERSION_BEFORE_2.17.0> sudo apt-mark hold fontconfig

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list fontconfig sudo dnf downgrade fontconfig-<VERSION_BEFORE_2.17.0> sudo dnf versionlock add fontconfig

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-34085?

fontconfig: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2026-34085 being exploited?

CVE-2026-34085 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-34085 affect?

CVE-2026-34085 affects fontconfig. Severity is medium (CVSS 5.9). 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.

How urgent is CVE-2026-34085?

Priority 21/100. No elevated risk signals yet.

References

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