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Fencer Vulns
medium 5.9

CVE-2026-34085 json

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,…

published 2026-03-25 7 mo ago modified 2026-07-18 3 mo ago also EUVD-2026-15934 , JLSEC-2026-79

cvss
5.9
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.1%
EPSS 0.1% chance of exploitation in 30 days, percentile 2%
public exploits
0
none known

Summary

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.

Patch / fix

  • julia Fontconfig_jll 2.17.1+0
  • fontconfig project fontconfig 2.17.1
  • fontconfig hummingbird 1 2.17.1-0.1.hum1

red hat advisories RHSA-2026:13722

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-34085 updated cvss 6.6

fontconfig: Fontconfig: Security flaw allows arbitrary code execution or system crash

  • Red Hat Enterprise Linux 6 fontconfig
    affected: workaround, no fix planned “Red Hat is not aware of a practical temporary workaround that fully mitigates this issue or meets Red Hat Product Security's standards for usability, deployment, applicability, or stability.”
  • Red Hat Hardened Images fontconfig 2.17.1-0.1.hum1
    fixed: vendor fix “Red Hat is not aware of a practical temporary workaround that fully mitigates this issue or meets Red Hat Product Security's standards for usability, deployment, applicability, or stability.” RHSA-2026:13722
  • Red Hat Enterprise Linux 7 fontconfig Red Hat Enterprise Linux 8 fontconfig, mingw-fontconfig, mingw32-fontconfig, mingw64-fontconfig Red Hat Enterprise Linux 9 fontconfig Red Hat Enterprise Linux 10 fontconfig
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
7 mo ago

Exploit prediction

0.13% chance of exploitation in the next 30 days, higher than 2% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 5.9 CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L
NVD 3.1 7.8 CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
OSV 3.1 7.8 CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Affected packages

ecosystem package affected fixed in
julia Fontconfig_jll
<2.17.1+0
2.17.1+0

Affected products

  • fontconfig project fontconfig

Classification

Weakness

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.