Low [CVE-2026-71391] off-by-one error via a malicious font file
This low-severity Red Hat Linux advisory covers CVE-2026-71391.
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Summary
GNU Emacs for Android contains an off-by-one error in the gvar table parser in src/sfnt.c.
The shared-coordinate index boundary check in sfnt_vary_simple_glyph() and sfnt_vary_compound_glyph() uses a strict greater-than comparison instead of greater-than-or-equal, allowing a crafted TrueType variable font to bypass the check and trigger a heap-based out-of-bounds read via memcpy.
An attacker can deliver a malicious font file via email, EWW (Emacs Web Wowser), or documents with custom faces, causing Emacs to load it. This exposes heap memory contents which can be later used to defeat ASLR.
This issue was fixed in commit 95ab9ef627b212d74d321c5bbb5b56a1be7b9fbe An off-by-one error can occur when a specially crafted font file is processed due to an improper bounds check. This can cause a heap-based buffer over-read, exposing heap memory contents.
To exploit this flaw, a user needs to load a malicious font file or a document with custom faces, limiting its exposure. The only security impact of this issue is an information disclosure of heap memory contents.
For these reasons, this vulnerability has been rated with a low severity. Red Hat severity: Low — CVSS 3.3 (CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:N).
Weakness: CWE-193.
Affected versions
No affected-version range was extracted from the source record. The vendor advisory is authoritative — check it before change work.
Official advisory · high-confidence parse· fetched 25 days ago·verify at source
Fixed versions
No fixed release is recorded yet. That does not prove no patch exists — confirm against the vendor advisory.
Official advisory · high-confidence parse· fetched 25 days ago·verify at source
Mitigation checklist
- Do not load untrusted font files or open unverified documents with custom faces.
Official advisory · high-confidence parse· fetched 25 days ago·verify at source
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