CVE-2026-23951 SumatraPDF's Integer Underflow in PalmDbReader Leads to Crash
An attacker can crash SumatraPDF by opening a crafted Mobi file, causing an integer underflow and out-of-bounds heap read.
- 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-2026-23951?
CVE-2026-23951 is a medium-severity vulnerability in sumatrapdfreader sumatrapdf, published on 22 Jan 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. All versions contain an off-by-one error in the validation code that only triggers with exactly 2 records, causing an integer underflow in the size calculation. This bug exists in PalmDbReader::GetRecord when opening a crafted Mobi file, resulting in an out-of-bounds heap read that crashes the app. There are no published fixes at the time of publication.
Which versions are affected by CVE-2026-23951?
It affects 1 product.
Products include Sumatrapdfreader Sumatrapdf.
How do I fix CVE-2026-23951?
No fix has been published for CVE-2026-23951 yet. Limit exposure of the affected software until one is available.
Is CVE-2026-23951 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-23951 exists.
Other vulnerabilities in sumatrapdfreader sumatrapdf
Sources
Also known as GHSA-hj4w-c5x8-p2hv.