CVE-2026-39378: nbconvert has an Arbitrary File Read via Path Traversal in HTMLExporter Image Embedding
Summary
When HTMLExporter.embedimages=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.
Patches
Upgrade to nbconvert 7.17.1
Workarounds
Do not enable HTMLExporter.embedimages (it is not enabled by default).
Other sources
The nbconvert tool, jupyter nbconvert, converts Jupyter notebooks to various other formats via Jinja templates. In versions 6.5 through 7.17.0, when HTMLExporter.embedimages=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. nbconvert 7.17.1 contains a fix. As a workaround, do not enable HTMLExporter.embedimages; it is not enabled by default.
— MITRE
Affected Software
Event History
Frequently Asked Questions
What is the severity of CVE-2026-39378?
CVE-2026-39378 has a high severity level due to the risk of arbitrary file read via path traversal.
How do I fix CVE-2026-39378?
To fix CVE-2026-39378, upgrade to nbconvert version 7.17.1 or later.
Which versions of nbconvert are affected by CVE-2026-39378?
CVE-2026-39378 affects nbconvert versions from 6.5 to 7.17.0.
What is the impact of CVE-2026-39378 on users?
CVE-2026-39378 allows an attacker to read arbitrary files on the system, which can lead to sensitive data exposure.
Is CVE-2026-39378 fixed in the latest release?
Yes, CVE-2026-39378 is fixed in nbconvert version 7.17.1.