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

Severity: medium (CVSS 5.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2026-01-22 · updated 2026-06-17
Weakness: CWE-125

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

sumatrapdfreader sumatrapdf: all versions

References

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

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