Quick answers
- Is CVE-2026-107738 exploited in the wild?
- No. Junglewise Threat Intelligence has no report of CVE-2026-107738 being exploited in the wild.
- How severe is CVE-2026-107738?
- Informational severity, published 8 October 2026.
- Which products and versions are affected?
- SumatraPDF 3.6.1 and earlier.
- Is there a fix for CVE-2026-107738?
- A patch was published on 2026-10-08. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
- How is CVE-2026-107738 attacked?
- It is attacked with local access, in a software library.
- Am I affected by CVE-2026-107738?
- Check whether you run SumatraPDF at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.
Technical details
ChmFile::GetCharZ() in the CHM parser fails to validate that file-controlled string offsets remain nonnegative after conversion from unsigned 32-bit integers to signed integers. Offsets from /#WINDOWS and /#IVB streams become negative, bypass the upper-bound check, and cause memchr() and strlen() to read before the /#STRINGS buffer. The vulnerability requires opening a malicious CHM file but only reliably causes application termination; memory disclosure has not been demonstrated.
Affected products
- SumatraPDF SumatraPDF 3.6.1 and earlier
Timeline
- 2026-07-29: disclosed
- 2026-10-08: patched