Vulnerability · Published Jan 22, 2026 · Assigned by GitHub_M

CVE-2026-23951SumatraPDF's Integer Underflow in PalmDbReader Leads to Crash

Medium 5.5

In plain English

A medium-severity out-of-bounds read in sumatrapdf from sumatrapdfreader. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 13% of all known vulnerabilities).

Severity (CVSS 3.1)5.5Medium

Exploit odds (30 days)0.2%top 87.3% of all CVEs

Exploited in the wildNo reportsCISA SSVC: poc

Attack toolingNoneno public tooling known

Official description

SumatraPDF is a multi-format reader for Windows. All versions contain an off-by-one error in the validation code that only triggers with exactly 2 records, causing an integer underflow in the size calculation. This bug exists in PalmDbReader::GetRecord when opening a crafted Mobi file, resulting in an out-of-bounds heap read that crashes the app. There are no published fixes at the time of publication.

Affected products (as reported)

Vendor	Product	Versions
sumatrapdfreader	sumatrapdf	<= 3.5.2rel

Weakness: CWE-125, CWE-191 · Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H

References

https://github.com/sumatrapdfreader/sumatrapdf/security/advisories/GHSA-hj4w-c5x8-p2hv x_refsource_CONFIRM
https://github.com/sumatrapdfreader/sumatrapdf/blob/master/src/PalmDbReader.cpp x_refsource_MISC