CVE-2026-39378 nbconvert has an Arbitrary File Read via Path Traversal in HTMLExporter Image Embedding

What is CVE-2026-39378?

CVE-2026-39378 is a medium-severity path traversal vulnerability in jupyter nbconvert, published on 21 Apr 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

Official description

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.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. nbconvert 7.17.1 contains a fix. As a workaround, do not enable `HTMLExporter.embed_images`; it is not enabled by default.

Weakness: CWE-73, CWE-22

Which versions are affected by CVE-2026-39378?

3 open source packages ship an affected version, including nbconvert. It affects 1 product.

Products include Jupyter Nbconvert.

How do I fix CVE-2026-39378?

Upgrade nbconvert to 7.17.1 or later.

Upgrade, and resolve every user-supplied path against an allowed base folder before opening it. More about Path traversal.

Is CVE-2026-39378 being exploited?

There is no known exploitation of CVE-2026-39378 in the wild and no public exploit code.

Other vulnerabilities in jupyter nbconvert

• CVE-2025-53000 nbconvert has an uncontrolled search path that leads to unauthorized code execution on Windows High 8.5
• CVE-2026-39377 nbconvert has an Arbitrary File Write via Path Traversal in Cell Attachment Filenames Medium 6.5

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as CLEANSTART-2026-RQ83656, CLEANSTART-2026-VX32079, DEBIAN-CVE-2026-39378, GHSA-7jqv-fw35-gmx9, PYSEC-2026-2230, UBUNTU-CVE-2026-39378.