SumatraPDF's Integer Underflow in PalmDbReader Leads to Crash

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.

Scores

EPSS (exploitation in 30 days)

0.22% · top 87% of all CVEs (6 Nov 2026)

CISA SSVC

Exploitation: poc · Automatable: no · Technical impact: partial

The list uses the assigner's score when there is one, then CISA's, then NVD's: Medium 5.5.

Weakness

• CWE-125: Out-of-bounds Read (opens in a new tab)All about CWE-125 and its CVEs
• CWE-191: Integer Underflow (Wrap or Wraparound) (opens in a new tab)All about CWE-191 and its CVEs
• CWE-193 (opens in a new tab)All about CWE-193 and its CVEs

Affected products

• sumatrapdfreader · sumatrapdf

  • affected <= 3.5.2rel

References (2)

• https://github.com/sumatrapdfreader/sumatrapdf/security/advisories/GHSA-hj4w-c5x8-p2hv (opens in a new tab)x_refsource_CONFIRM
• https://github.com/sumatrapdfreader/sumatrapdf/blob/master/src/PalmDbReader.cpp (opens in a new tab)x_refsource_MISC

Sources

The same CVE in the primary databases and aggregators, to check against.

• CVE.org record (opens in a new tab)
• CVE List JSON (GitHub) (opens in a new tab)
• NVD (opens in a new tab)
• FIRST EPSS (opens in a new tab)
• OSV.dev (opens in a new tab)
• GitHub Advisories (opens in a new tab)
• CIRCL Vulnerability-Lookup (opens in a new tab)

Badge for a README or a ticket

[![CVE-2026-23951](https://trackcve.app/badge/CVE-2026-23951.svg)](https://trackcve.app/cve/CVE-2026-23951)

Record last updated 22 Jan 2026, 21:44 UTC.