CVE-2026-23951Public exploit

Application crash via underflowed Mobi record size

Published Jan 22, 2026 · Updated Jan 22, 2026

Out-of-bounds read in SumatraPDF 3.5.2 and earlier allows attackers to crash the application by supplying a crafted Mobi file. PdbReader::ParseHeader skips offset-order validation for exactly two records, and PdbReader::GetRecord subtracts inverted offsets after only logging the invalid order, wrapping the record size before downstream parsing reads beyond the heap buffer. Exploitation requires a user to open the malicious file and affects availability only through an application crash.

CVSS severity5.5
Medium
EPSS probability0.21%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Out-of-bounds read in SumatraPDF 3.5.2 and earlier allows attackers to crash the application by supplying a crafted Mobi file. PdbReader::ParseHeader skips offset-order validation for exactly two records, and PdbReader::GetRecord subtracts inverted offsets after only logging the invalid order, wrapping the record size before downstream parsing reads beyond the heap buffer. Exploitation requires a user to open the malicious file and affects availability only through an application crash.

The record

CVE
CVE-2026-23951
Published
Jan 22, 2026
Updated
Jan 22, 2026
Vendor
SumatraPDF
Product
SumatraPDF
Classifications
CWE-125, CWE-191, CWE-193, T1204.002
Attack vector
local
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jan 22, 2026CVE publishedPublication date reported by the CVE source.
  2. Jan 22, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=<= 3.5.2rel

What conditions does exploitation require?

Attack vectorlocal
Required privilegesunauthenticated

What is affected?

SumatraPDF · SumatraPDFversion=<= 3.5.2rel

Published CVSS scores

5.5GitHub, Inc.CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-125Out-of-bounds Read
CWE-191Integer Underflow (Wrap or Wraparound)
CWE-193Off-by-one Error
T1204.002Malicious File

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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