The flaw lies in the extract_pictures function of calibre, which only verifies that file names begin with "Pictures" and fails to normalize or strip ".." sequences. An attacker can embed path traversal entries in a ZIP to overwrite any file in directories where calibre has write access. On Windows, writing a malicious payload to the Startup folder enables code execution the next time the user logs in. This provides uncontrolled file writes and, in the Windows scenario, remote code execution, making the vulnerability a high‑severity issue.

Affected products are kovidgoyal’s calibre e‑book manager. Versions 9.2.1 and earlier are vulnerable. The developers addressed the issue in version 9.3.0, which removes the unsafe extract_pictures implementation.

CVSS scoring assigns 9.3, indicating critical severity, while the EPSS score is below 1%, implying a very low current exploitation likelihood. The vulnerability is not listed in the CISA KEV catalog, suggesting no widespread active exploits. Nevertheless, successful exploitation requires only local interaction with calibre and sufficient file‑write permissions; on Windows the ability to place a payload in the Startup folder turns local access into remote code execution. The combination of high severity and the straightforward local attack path warrants urgent remediation.