SumatraPDF up to 3.6.1 ChmFile ChmFile::GetCharZ buffer overflow

Summaryinfo

A vulnerability was found in SumatraPDF up to 3.6.1 and classified as problematic. Affected is the function ChmFile::GetCharZ of the component ChmFile. Executing a manipulation can lead to buffer overflow. This vulnerability appears as CVE-2026-107738. The attack may be performed from remote. There is no available exploit.

Detailsinfo

A vulnerability has been found in SumatraPDF up to 3.6.1 and classified as problematic. This vulnerability affects the function ChmFile::GetCharZ of the component ChmFile. The manipulation with an unknown input leads to a buffer overflow vulnerability. The CWE definition for the vulnerability is CWE-120. The product copies an input buffer to an output buffer without verifying that the size of the input buffer is less than the size of the output buffer, leading to a buffer overflow. As an impact it is known to affect availability. CVE summarizes:

SumatraPDF is a multi-format reader for Windows. In 3.6.1 and earlier, ChmFile::GetCharZ() narrows file-controlled unsigned string offsets from /#WINDOWS and /#IVB to signed integers without a lower-bound check. An offset that becomes negative can make the function read before the /#STRINGS buffer, causing deterministic application termination. No broader impact is claimed beyond the advisory-supported conditions. No fixed version is available as of this review.

The advisory is available at github.com. This vulnerability was named CVE-2026-107738 since 10/08/2026. The exploitation appears to be easy. The attack can be initiated remotely. No form of authentication is required for a successful exploitation. Successful exploitation requires user interaction by the victim. Technical details are known, but there is no available exploit. The structure of the vulnerability defines a possible price range of USD $0-$5k at the moment (estimation calculated on 10/09/2026).

There is no information about possible countermeasures known. It may be suggested to replace the affected object with an alternative product.

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Productinfo

Name

• SumatraPDF

Version

• 3.6.0
• 3.6.1

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