---
id: CVE-2026-107729
title: SumatraPDF is a multi-format reader for Windows
summary: >-
  SumatraPDF is a multi-format reader for Windows. In 3.7.0.22298,
  src/MobiDoc.cpp narrows the untrusted unsigned mobiHdr.hdrLen field to a
  signed integer for validation; values above INT_MAX become negative and bypass
  the upper-bound chec…
severity: medium
cvss: 5.5
cvssVector: 'CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H'
cwe:
  - CWE-125
published: '2026-10-08'
updated: '2026-10-08'
sourceUpdated: '2026-10-08T23:16:58.490'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-107729'
references:
  - url: >-
      https://github.com/sumatrapdfreader/sumatrapdf/commit/1ef900cbad02f06353b0a0747b098ca596f7c131
    label: security-advisories@github.com
  - url: >-
      https://github.com/sumatrapdfreader/sumatrapdf/security/advisories/GHSA-86hq-m6hv-67h2
    label: security-advisories@github.com
tags:
  - nvd
ingestedAt: '2026-10-09T00:19:50.969Z'
---

## Overview

SumatraPDF is a multi-format reader for Windows. In 3.7.0.22298, src/MobiDoc.cpp narrows the untrusted unsigned mobiHdr.hdrLen field to a signed integer for validation; values above INT_MAX become negative and bypass the upper-bound check. When the EXTH flag is set, the original unsigned value is reused as a pointer offset, causing DecodeExthHeader() to read beyond the record buffer. Opening a crafted MOBI file can reliably terminate the application with a native access violation; no code execution, information disclosure, or integrity impact has been demonstrated. No fixed version is available as of this review.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.