CVE-2026-39378 — nbconvert
MEDIUMCVE-2026-39378 is a medium-severity (CVSS 6.5) Path Traversal vulnerability in nbconvert. A fix is available for nbconvert — see the affected versions and patch details below.
nbconvert has an Arbitrary File Read via Path Traversal in HTMLExporter Image Embedding
Exploitation Status
No confirmed exploitation observed yet
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-39378.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2026-39378 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 379,145 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
nbconvertReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.
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.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | nbconvert | ≥ 6.5.0&&< 7.17.1 | 7.17.1pip install --upgrade 'nbconvert==7.17.1' |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for nbconvert, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update nbconvert to 7.17.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-39378 is resolved across your whole dependency graph.
Workarounds
Resolve every user-supplied path to its canonical form and reject anything that escapes the intended directory, and run the component under an account that has no read or write access outside the directory it legitimately serves.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-39378 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2026-39378. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
This Moderate impact flaw in nbconvert allows for sensitive file exfiltration through path traversal in image references. The vulnerability is exploitable only when the `HTMLExporter.embed_images` setting is explicitly enabled. This setting is not enabled by default in the nbconvert.
To mitigate this vulnerability, ensure that the `HTMLExporter.embed_images` setting in nbconvert is not enabled. This setting is disabled by default, therefore no action is required unless it has been explicitly enabled in your environment. If this setting has been enabled, disabling it will prevent the path traversal vulnerability from being exploited.Source: Red Hat security advisory for CVE-2026-39378 (CC BY 4.0)
Frequently Asked Questions
Is CVE-2026-39378 in your dependencies?
O3 Security finds CVE-2026-39378 across PyPI dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.