How severe is CVE-2026-42305?

CVE-2026-42305 has a CVSS score of 8.8/10, rated HIGH. Immediate patching is strongly recommended.

Which packages are affected by CVE-2026-42305?

CVE-2026-42305 affects the following packages: dulwich (PyPI). Ecosystems affected: PyPI.

How do I fix CVE-2026-42305?

Update dulwich to 1.2.5 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-42305 is resolved across your whole dependency graph.

How do I detect CVE-2026-42305 in my PyPI dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for dulwich, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-42305 if there is no patch (or I can't update yet)?

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.

Is CVE-2026-42305 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-42305 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-42305?

CVE-2026-42305 has an EPSS (Exploit Prediction Scoring System) score of 0.9%, placing it in the 57th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-42305?

CVE-2026-42305 is classified as Path Traversal (CWE-22). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation. This is a high-impact weakness class that often enables remote code execution or data exposure.

When was CVE-2026-42305 published, and has it been updated?

CVE-2026-42305 was published on June 10, 2026 and was last updated on August 12, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐍

🐍 PyPI

Not in CISA KEV

HIGH severity

CVE-2026-42305 — dulwich

HIGHFix: jelmer/dulwich@49eb56e

CVE-2026-42305 is a high-severity (CVSS 8.8) Path Traversal vulnerability in dulwich. A fix is available for dulwich — see the affected versions and patch details below.

Dulwich has an arbitrary file write via NTFS-hostile tree entries on Windows

Also known asGHSA-897w-fcg9-f6xjPYSEC-2026-2463

Published

Jun 10, 2026

Updated

Aug 12, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Sep 27, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

A successful exploit gives an attacker total control of the affected component, not partial access.
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-2026-42305.

EPSS Exploitation Probability

via FIRST.org ↗

0.9%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs57th percentile — riskier than 57% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

CVE-2026-42305 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 379,842 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

1 pkg affected

🐍dulwich

Real-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

Impact

Arbitrary file write leading to remote code execution when cloning or checking out a malicious Git repository on Windows.

Dulwich's path-element validator accepted tree entries whose filenames contained bytes that Windows interprets as structural path syntax:

\ — the Windows path separator. A single tree entry named .git\hooks\pre-commit.exe was treated as one valid filename on POSIX but materialized as nested directories .git/hooks/pre-commit.exe on Windows, planting a file inside the victim's .git directory. Git for Windows then executes that hook on the next git commit, giving the attacker arbitrary code execution in the victim's user context. The same primitive can be used with ..\outside.txt to escape the work tree.
: — the NTFS alternate-data-stream marker. .git::$INDEX_ALLOCATION writes directly into the victim's .git entity, bypassing the .git-as-a-directory check.
git~<digits> — NTFS 8.3 short-name aliases of .git. Only the literal git~~1 was rejected; git~~2, git~~10, GIT~~1, etc. were all accepted.

Contributing configuration bugs made matters worse. The core.protectNTFS and core.protectHFS settings were looked up under a wrong option name and so user-set values were silently ignored, and core.protectNTFS only defaulted to true on Windows (Git upstream has defaulted it to true everywhere since CVE-2019-1353). Both have been corrected.

Anyone who clones, fetches, or checks out an untrusted repository with Dulwich on Windows - either through the Dulwich CLI, porcelain.clone, or any downstream tool built on Dulwich - is impacted. POSIX clones are not directly exploitable (on POSIX \ is a literal filename byte), but a POSIX user can unknowingly propagate a malicious tree to Windows consumers via push or re-publication.

Patches

Fixed in Dulwich 1.2.5. Users should upgrade to 1.2.5 or later.

The fix lives in three commits:

Read core.protectNTFS / core.protectHFS under their documented option names so user-set values are honored.
Default core.protectNTFS to true on every platform, matching Git's PROTECT_NTFS_DEFAULT=1.
Reject , :, and all git~<digits> 8.3 short-name forms in validate_path_element_ntfs.

Workarounds

There is no effective pre-patch workaround. On affected versions the core.protectNTFS configuration key was silently ignored, so setting it to true does not mitigate the issue. Users who cannot upgrade should avoid cloning, fetching, or checking out untrusted repositories with Dulwich on Windows. After upgrading the NTFS validator is on by default on every platform, so no additional configuration is required.

Resources

Git upstream path validation: https://github.com/git/git/blob/master/path.c (is_ntfs_dotgit, verify_path)
CVE-2019-1353 — the Git upstream vulnerability that established core.protectNTFS = true as the cross-platform default
CVE-2019-1354 — backslash-in-tree-path class in Git, analogous to this issue

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐍PyPI	`dulwich`	≥ 0.10.0&&< 1.2.5	1.2.5`pip install --upgrade 'dulwich==1.2.5'`

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for dulwich, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update dulwich to 1.2.5 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-42305 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.

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.

Red HatImportant

This is an Important flaw in Dulwich, a Python Git library, primarily impacting Windows systems. While Red Hat Enterprise Linux and other POSIX-based Red Hat products are not directly vulnerable to remote code execution, they can serve as vectors for propagating malicious Git repositories to Windows clients.…

Workaround published by Red Hat

Mitigation for this issue involves avoiding the cloning, fetching, or checking out of untrusted Git repositories with Dulwich. This operational control is crucial for preventing the introduction and propagation of malicious content, especially when Red Hat systems interact with or serve Windows clients that utilize Dulwich.

Source: Red Hat security advisory for CVE-2026-42305 (CC BY 4.0)

Product	Fixed in	Advisory
Red Hat OpenShift AI 3.4	`rhoai/odh-kserve-storage-initializer-rhel9:1787073479`	RHSA-2026:60520

Frequently Asked Questions

## Impact Arbitrary file write leading to remote code execution when cloning or checking out a malicious Git repository on Windows. Dulwich's path-element validator accepted tree entries whose filenames contained bytes that Windows interprets as structural path syntax: - \ — the Windows path separator. A single tree entry named .git\hooks\pre-commit.exe was treated as one valid filename on POSIX but materialized as nested directories .git/hooks/pre-commit.exe on Windows, planting a file inside the victim's .git directory. Git for Windows then executes that hook on the next git commit, g