Out-of-bounds Read in Sumatrapdfreader Sumatrapdf

CVE-2026-23951

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.

Vulnerability class: Buffer Overflow

Published · last modified .

CVSS v3 metric

CVSS v3 base score 5.5 (Medium). Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H.

EPSS exploit prediction

EPSS: 0.002 (11.7th percentile), scored .

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 12th percentile — 11.7% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS trend (30 days)EPSS over the last 30 days for CVE-2026-23951: held from 0.002 to 0.002.

EPSS over last 30 days · oldest: 0.002 · newest: 0.002 · change: +0.000

Affected products

Weakness classification (CWE)

References

Frequently asked questions

What is CVE-2026-23951?
CVE-2026-23951 is a medium-severity vulnerability in Sumatrapdfreader Sumatrapdf, classified under Out-of-bounds Read. CVSS score: 5.5/10. Published 2026-01-22.
How severe is CVE-2026-23951?
Medium severity. CVSS v3 base score is 5.5 out of 10.