CVE-2026-25920 SumatraPDF has a heap out-of-bounds read in MOBI HuffDic decompressor

Q: Is CVE-2026-25920 being exploited?

There is no known exploitation of CVE-2026-25920 in the wild and no public exploit code.

Q: How do I fix CVE-2026-25920?

No fix has been published for CVE-2026-25920 yet. Limit exposure of the affected software until one is available.

Medium 5.5 Published 9 Feb 2026 Updated 11 Feb 2026

An attacker can cause a denial of service by tricking a user into opening a crafted MOBI file in SumatraPDF.

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-2026-25920?

CVE-2026-25920 is a medium-severity memory corruption vulnerability in sumatrapdfreader sumatrapdf, published on 9 Feb 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 3.5.2 and earlier, a heap out-of-bounds read vulnerability exists in SumatraPDF's MOBI HuffDic decompressor. The bounds check in AddCdicData() only validates half the range that DecodeOne() actually accesses. Opening a crafted .mobi file can read nearly (1 << codeLength) bytes beyond the CDIC dictionary buffer, leading to a crash.

Weakness: CWE-125

Which versions are affected by CVE-2026-25920?

It affects 1 product.

Products include Sumatrapdfreader Sumatrapdf.

How do I fix CVE-2026-25920?

No fix has been published for CVE-2026-25920 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-2026-25920 being exploited?

There is no known exploitation of CVE-2026-25920 in the wild and no public exploit code.

Sources

Also known as GHSA-5mwx-65x7-cffp.