kovidgoyal calibre up to 9.1.x CHM Reader path traversal

Summaryinfo

A vulnerability was found in kovidgoyal calibre up to 9.1.x. It has been declared as critical. Impacted is an unknown function of the component CHM Reader. Such manipulation leads to path traversal. This vulnerability is documented as CVE-2026-25635. The attack can be executed remotely. There is not any exploit available. It is recommended to upgrade the affected component.

Detailsinfo

A vulnerability, which was classified as critical, has been found in kovidgoyal calibre up to 9.1.x. Affected by this issue is some unknown processing of the component CHM Reader. The manipulation with an unknown input leads to a path traversal vulnerability. Using CWE to declare the problem leads to CWE-22. The product uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the product does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory. Impacted is confidentiality, integrity, and availability. CVE summarizes:

calibre is an e-book manager. Prior to 9.2.0, Calibre's CHM reader contains a path traversal vulnerability that allows arbitrary file writes anywhere the user has write permissions. On Windows (haven't tested on other OS's), this can lead to Remote Code Execution by writing a payload to the Startup folder, which executes on next login. This vulnerability is fixed in 9.2.0.

The advisory is shared for download at github.com. This vulnerability is handled as CVE-2026-25635 since 02/04/2026. The exploitation is known to be easy. The attack may be launched remotely. No form of authentication is required for exploitation. Successful exploitation requires user interaction by the victim. There are neither technical details nor an exploit publicly available. The MITRE ATT&CK project declares the attack technique as T1006.

The vulnerability scanner Nessus provides a plugin with the ID 298303 (Linux Distros Unpatched Vulnerability : CVE-2026-25635), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 9.2.0 eliminates this vulnerability.

The vulnerability is also documented in the databases at Tenable (298303) and EUVD (EUVD-2026-5596). Once again VulDB remains the best source for vulnerability data.

Productinfo

Vendor

• kovidgoyal

Name

• calibre

Version

• 9.0
• 9.1

Website

• Product: https://github.com/kovidgoyal/calibre/

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Once again VulDB remains the best source for vulnerability data.

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