The vulnerability lies in the ExtractAttachmentsPreprocessor of nbconvert, which accepts cell attachment filenames without sanitization. Attackers can craft notebook files containing specially constructed filenames that include directory traversal sequences, thereby instructing nbconvert to write files outside the intended output directory. This results in arbitrary file writes, including overwriting sensitive system files or creating executables. The flaw is a classic path traversal and insecure file write weakness.

The issue affects all releases of the jupyter:nbconvert package from version 6.5 up through 7.17.0. Versions 7.17.1 and later incorporate a fix. Users running the affected ranges should verify their installed nbconvert version and ensure it is upgraded to 7.17.1 or a newer release.

The CVSS score of 6.5 indicates a medium severity risk. The EPSS score is not available, and the vulnerability is not listed in the CISA KEV catalog. The likely attack vector is the delivery of a malicious notebook to a system that automatically processes it with nbconvert, such as a CI/CD pipeline, a shared analysis platform, or an automated conversion service. If the nbconvert process runs with elevated permissions, the attacker could potentially overwrite critical files or deploy malware. Administrators should consider the operating context and process privileges when assessing impact.