Quick answers
- Is CVE-2026-59679 exploited in the wild?
- No. Junglewise Threat Intelligence has no report of CVE-2026-59679 being exploited in the wild.
- How severe is CVE-2026-59679?
- Critical severity, with a CVSS score of 9, published 10 September 2026.
- Which products and versions are affected?
- X.Org libXfont2.
- Is there a fix for CVE-2026-59679?
- No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.
- How is CVE-2026-59679 attacked?
- It is attacked over the network.
- Am I affected by CVE-2026-59679?
- Check whether you run X.Org libXfont2. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.
Technical details
The vulnerability exists in fs_read_glyphs() in src/fc/fserve.c, where the function indexes a per-character encoding[] array using num_chars from an FS_QueryXBitmaps16 reply. However, the array was allocated with a size derived from num_extents in a separate FS_QueryXExtents16 reply. These two CARD32 fields are never cross-checked, allowing a mismatch. An attacker controlling a font server can send a small num_extents (e.g., 1) in the extents reply followed by a large num_chars (e.g., 100,000) in the bitmaps reply, causing out-of-bounds heap read and write operations. No authentication is required, as the attack occurs at the font server protocol level. Exploitation leads to memory corruption and potential code execution.
Affected products
- X.Org libXfont2
Timeline
- 2026-09-10: disclosed