CVE-2026-107729 SumatraPDF: Unsigned-to-signed hdrLen validation bypass in SumatraPDF MOBI parsing causes out-of-bounds read
An attacker can cause a denial of service in SumatraPDF by tricking a user into opening a crafted MOBI file that triggers an out-of-bounds read via integer overflow.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- A user has to click or open something
- Fix
- None listed
What is CVE-2026-107729?
CVE-2026-107729 is a medium-severity vulnerability in sumatrapdfreader sumatrapdf, published on 8 Oct 2026. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.
Official description
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.
Weakness: CWE-125
Which versions are affected by CVE-2026-107729?
How do I fix CVE-2026-107729?
No fix has been published for CVE-2026-107729 yet. Limit exposure of the affected software until one is available.
Is CVE-2026-107729 being exploited?
There is no known exploitation of CVE-2026-107729 in the wild and no public exploit code.
Sources
Also known as GHSA-86hq-m6hv-67h2.