GUIX binary resource loader: unvalidated glyph range causes an integer underflow and a heap out-of-bounds write when loading an untrusted font or theme

published 2026-10-20 19 d ago modified 2026-10-20 19 d ago also EUVD-2026-105040

cvss: 7.1; version 4.0, 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

The GUIX binary resource loader never checks that a font page's glyph range is well formed. `gx_page_header_first_glyph` and `gx_page_header_last_glyph` are read verbatim from the file and only the upper bound of `last_glyph` is validated, so a page declaring `first_glyph > last_glyph` makes `last - first + 1` underflow to a very large unsigned count.

That count is multiplied by a glyph record size to reserve the load buffer, and the multiply is unchecked, so it wraps to a small value and the loader allocates a buffer far smaller than the data it is about to write. The load pass then recomputes the count in a narrower type and writes attacker-controlled glyph records into the undersized buffer.

Patch / fix

fixed in 1

Eclipse Foundation Eclipse ThreadX - GUIX 6.5.2.202603

CISA SSVC

Exploitation: none
Automatable: no
Technical impact: total
Assessed: 19 d ago (2026-10-20)

Exploit prediction

0.14% 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	4.0	7.1	CVSS:4.0/AV:L/AC:H/AT:N/PR:N/UI:A/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
CNA	4.0	7.1	CVSS:4.0/AV:L/AC:H/AT:N/PR:N/UI:A/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Affected products

Eclipse Foundation Eclipse ThreadX - GUIX

Classification

Weakness

CWE-190 Integer Overflow or Wraparound
CWE-680 Integer Overflow to Buffer Overflow
CWE-787 Out-of-bounds Write

References

github.com /eclipse-threadx/guix/security/advisories/GHSA-hgcj-22cg-4hfv

Sources

CVE List CVE-2026-91189
NVD CVE-2026-91189

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.

Summary