CVE-2026-107738 SumatraPDF: Untrusted binary record offset used without lower-bound validation
Attackers can cause SumatraPDF to crash by providing a malicious CHM file with invalid string offsets, leading to application termination.
- 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-2026-107738?
CVE-2026-107738 is a medium-severity denial of service 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 3.6.1 and earlier, ChmFile::GetCharZ() narrows file-controlled unsigned string offsets from /#WINDOWS and /#IVB to signed integers without a lower-bound check. An offset that becomes negative can make the function read before the /#STRINGS buffer, causing deterministic application termination. No broader impact is claimed beyond the advisory-supported conditions. No fixed version is available as of this review.
Weakness: CWE-125
Which versions are affected by CVE-2026-107738?
How do I fix CVE-2026-107738?
No fix has been published for CVE-2026-107738 yet. Limit exposure of the affected software until one is available.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-107738 being exploited?
There is no known exploitation of CVE-2026-107738 in the wild and no public exploit code.
Sources
Also known as GHSA-33jg-vxm6-8mxx.