CVE-2026-23951: SumatraPDF is a multi-format reader for Windows

Routine

MEDIUM 5.5MITIGATE

CVE-2026-23951 is a medium-severity flaw (CVSS 5.5) affecting sumatrapdf. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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.

Why this priority

Public exploit reference

No fix is published yet: follow the downgrade or mitigation steps.

Risk facts

CVSS score	5.5 (Medium)
Attack vector	Local
Attack complexity	Low
Privileges needed	None
User interaction	Required
EPSS exploit chance	0.2% (top 87%)
CISA exploited list	No
Weakness	CWE-125, CWE-191, CWE-193
Published	2026-01-22
Last modified	2026-06-17

Publisher (CNA): GitHub, Inc. · Vendor: sumatrapdfreader

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-01-22 01:15 UTCPublished CVE record published
2026-06-17 10:22 UTCUpdated Record last modified

sumatrapdfreader sumatrapdf MITIGATE

Affected: all versions

Fixed in: no fixed release known

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy sumatrapdf || rpm -q sumatrapdf || sumatrapdf --version

No fixed or unaffected release known

Apply the vendor mitigation from the advisory, disable the affected feature, or restrict network access.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-23951?

sumatrapdf: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2026-23951 being exploited?

CVE-2026-23951 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-23951 affect?

CVE-2026-23951 affects sumatrapdf. Severity is medium (CVSS 5.5). 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 PalmDbReade

How urgent is CVE-2026-23951?

Priority 27/100. Public exploit reference

Software pages

Windows vulnerabilities

Related CVEs

CVE-2026-23512 HIGH 8.6 UPGRADE SumatraPDF is a multi-format reader for Windows
CVE-2025-57248 HIGH 7.3 DOWNGRADE A null pointer dereference vulnerability was discovered in SumatraPDF 3.5.2 during the processing of a crafted

References

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