CVE-2026-59679
HIGHDescription
fs_read_glyphs() in the libXfont2 font-server client (src/fc/fserve.c) indexes the per-character encoding[] array using num_chars from the FS_QueryXBitmaps16 reply, but that array was allocated with a size derived from num_extents in the separate FS_QueryXExtents16 reply. The two CARD32 fields are never cross-checked. A malicious or compromised font server can send a small num_extents (e.g. 1) in the extents reply, then a large num_chars (e.g. 100000) in the bitmaps reply. This causes attacker-controlled out-of-bounds heap read and writes.
How to fix
This vulnerability affects an unusually large number of packages. The highest-confidence fixes are shown above; the full list is longer. Check the referenced advisories for complete coverage.
TridentStack Control can deploy fixes like this automatically across your Windows, macOS, and Linux fleet. See how it works
Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.
CVSS v3 Vector
Exploitability
Impact
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H
Exploit Intelligence
Low risk: more likely to be exploited than 35% of all known CVEs.
References
Related Vulnerabilities
Other CWE-787 (Out-of-bounds Write) vulnerabilities, ordered by exploit likelihood. View all
| CVE | Severity | CVSS | EPSS | Exploited | Fix |
|---|---|---|---|---|---|
| CVE-2025-22457 | Critical | 9.0 | 100% | KEV + Ransom | Fix |
| CVE-2025-0282 | Critical | 9.0 | 100% | KEV + Ransom | - |
| CVE-2023-4863 | High | 8.8 | 100% | KEV | Fix |
| CVE-2015-3113 | Critical | 9.8 | 100% | KEV | Fix |
| CVE-2021-20038 | Critical | 9.8 | 100% | KEV + Ransom | - |
| CVE-2019-11043 | High | 8.7 | 100% | KEV + Ransom | Fix |
Common questions
How do I fix CVE-2026-59679?
Published advisories record a fix for 9 affected products. The "How to fix" section on this page lists the fixed version and source advisory for each one, so apply the entry matching what you actually run.
Is CVE-2026-59679 being actively exploited?
Not that we know of. CVE-2026-59679 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 0.41% is the estimated probability that it will be exploited in the next 30 days. That is higher than 35% of all scored CVEs.
How severe is CVE-2026-59679?
CVE-2026-59679 has a CVSS v3 base score of 9.0, rated important. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.
What does CVE-2026-59679 affect?
Published advisories record a fix for libxfont (Debian), libXfont2 (Red Hat / RHEL), libXfont2 (Rocky), libXfont2-debuginfo (Rocky), and 5 more. Only products with a sourced advisory are listed, so treat this as what we can cite rather than a complete inventory.
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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-09-10.