Vulnerability · Published Oct 8, 2026 · Assigned by GitHub_M

CVE-2026-107738SumatraPDF: Untrusted binary record offset used without lower-bound validation

Medium 6.8

In plain English

A medium-severity out-of-bounds read in sumatrapdf from sumatrapdfreader. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.1% (higher than 2% of all known vulnerabilities).

Severity (CVSS 4.0)6.8Medium

Exploit odds (30 days)0.1%top 98.2% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official description

SumatraPDF is a multi-format reader for Windows. In 3.6.1 and earlier, ChmFile::GetCharZ() narrows file-controlled unsigned string offsets from /#WINDOWS and /#IVB to signed integers without a lower-bound check. An offset that becomes negative can make the function read before the /#STRINGS buffer, causing deterministic application termination. No broader impact is claimed beyond the advisory-supported conditions. No fixed version is available as of this review.

Affected products (as reported)

Vendor	Product	Versions
sumatrapdfreader	sumatrapdf	<= 3.6.1

Weakness: CWE-125 · Vector: CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

References

https://github.com/sumatrapdfreader/sumatrapdf/security/advisories/GHSA-33jg-vxm6-8mxx x_refsource_CONFIRM
https://github.com/sumatrapdfreader/sumatrapdf/commit/62254ed6d781ceb5cd16489bb423e7f591cd72c4 x_refsource_MISC