CVE-2026-26054

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.

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