CVE-2026-39377 | nbconvert has an Arbitrary File Write via Path Traversal in Cell Attachment Filenames

The nbconvert tool, jupyter nbconvert, converts Jupyter notebooks to various other formats via Jinja templates. Versions 6.5 through 7.17.0 allow arbitrary file writes to locations outside the intended output directory when processing notebooks containing crafted cell attachment filenames. The `ExtractAttachmentsPreprocessor` passes attachment filenames directly to the filesystem without sanitization, enabling path traversal attacks. This vulnerability provides complete control over both the destination path and file extension. Version 7.17.1 contains a patch.

Published: 2026-04-21 Last update: 2026-04-23 Assigner: [email protected] Source: [email protected]
NVD Status：Analyzed，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2026-39377 is rated Low Risk (29.1/100): CVSS Medium severity, with low exploitation likelihood (EPSS 0.03%). Monitor for updates and reassess as exploit intelligence or EPSS changes.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2026-39377

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-04-21 — 0.03% —

Full EPSS history (1 record total)

Common vulnerability scoring system (CVSS) metrics for CVE-2026-39377

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
6.5 3.1 MEDIUM
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:R)
A real person has to do something—click, install, enable—otherwise it doesn’t land.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:N)
Service keeps running; no real outage angle.
 2.8 3.6 [email protected]

Weakness enumeration for CVE-2026-39377

GitHub Security Advisory for CVE-2026-39377

GHSA-4c99-qj7h-p3vg · Severity: medium · Ecosystem: pip — nbconvert has an Arbitrary File Write via Path Traversal in Cell Attachment Filenames

OS Trackers for CVE-2026-39377

vendor priority summary link
debian unimportant CVE-2026-39377 unimportant priority: Debian including 1 source packages (nbconvert), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 4, open 1. https://security-tracker.debian.org/tracker/CVE-2026-39377
redhat medium — https://access.redhat.com/security/cve/CVE-2026-39377
ubuntu medium CVE-2026-39377 medium priority: Ubuntu including 1 source packages (nbconvert), 7 status rows across 7 suites (bionic, focal, jammy, noble, questing, resolute, upstream): needs-triage 7. https://ubuntu.com/security/CVE-2026-39377

Affected software / configurations for CVE-2026-39377

Vendor Product Version Raw CPE
jupyter nbconvert >= 6.5.0, < 7.17.1 cpe:2.3:a:jupyter:nbconvert:*:*:*:*:*:python:*:*

References for CVE-2026-39377

cvelogic Threat Intelligence