When HTMLExporter.embed_images=True, nbconvert's markdown renderer allows arbitrary file read via path traversal in image references. A malicious notebook can exfiltrate sensitive files from the conversion host by embedding them as base64 data URIs in the output HTML.
Upgrade to nbconvert 7.17.1
Do not enable HTMLExporter.embed_images (it is not enabled by default).
{
"cwe_ids": [
"CWE-22",
"CWE-23"
],
"github_reviewed": true,
"github_reviewed_at": "2026-04-21T17:18:53Z",
"nvd_published_at": "2026-04-21T01:16:06Z",
"severity": "MODERATE"
}