Vulnerability · Published Sep 24, 2026 · Assigned by GitHub_M

CVE-2026-26054SumatraPDF: Heap out-of-bounds read in MOBI header parser.

Medium 6.8

In plain English

A medium-severity out-of-bounds read in sumatrapdf from sumatrapdfreader. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 11% of all known vulnerabilities).

Severity (CVSS 4.0)6.8Medium

Exploit odds (30 days)0.2%top 88.8% of all CVEs

Exploited in the wildNo reportsCISA SSVC: poc

Attack toolingNoneno public tooling known

Official description

SumatraPDF is a multi-format reader for Windows. Prior to 3.6, the MobiDoc::ParseHeader function in src/MobiDoc.cpp validates a record using kMobiHeaderMinLen but DecodeMobiDocHeader constructs a decoder sized for kMobiHeaderLen without receiving the actual remaining buffer length. A malformed MOBI file can use an attacker-controlled header length to bypass optional-field early returns and cause the decoder to read beyond a short heap buffer. Opening the crafted document can crash SumatraPDF. This issue is fixed in version 3.6.

Affected products (as reported)

Vendor	Product	Versions
sumatrapdfreader	sumatrapdf	< 3.6

Weakness: CWE-125 · Vector: CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

References

https://github.com/sumatrapdfreader/sumatrapdf/security/advisories/GHSA-27p6-wrfp-pgm8 x_refsource_CONFIRM
https://github.com/sumatrapdfreader/sumatrapdf/issues/5318 x_refsource_MISC
https://github.com/sumatrapdfreader/sumatrapdf/commit/24b9ce83383bbaa48b3efe00e4d30cccea126198 x_refsource_MISC
https://github.com/sumatrapdfreader/sumatrapdf/releases/tag/3.6rel x_refsource_MISC