CVE-2026-107737 SumatraPDF CHM `its://` signed index causes an out-of-bounds object lookup
Attackers can cause a crash in SumatraPDF by opening a crafted CHM file when the IE fallback backend is used, leading to denial of service.
- 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-2026-107737?
CVE-2026-107737 is a medium-severity memory corruption 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, and in pre-release 3.7.0.20369 when WebView2 is absent or cannot initialize, ParseProtoUrl() accepts the signed host component of an its:// URL and FindHtmlWindowById() uses it directly as an index into gHtmlWindows. Opening a crafted CHM through the IE fallback backend with a negative or otherwise out-of-range window identifier can cause an out-of-bounds pointer read followed by an invalid object callback dereference and process termination. No fixed version is available as of this review.
Weakness: CWE-129
Which versions are affected by CVE-2026-107737?
How do I fix CVE-2026-107737?
No fix has been published for CVE-2026-107737 yet. Limit exposure of the affected software until one is available.
Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.
Is CVE-2026-107737 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-107737 exists.
Sources
Also known as GHSA-8p34-f32f-7rmq.