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High, CVSS 8.8amended

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

CVE-2026-42305GHSA-897w-fcg9-f6xj

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (dulwich 1.2.5), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

  • PyPI dulwich

    Affected
    >= 0.10.0, < 1.2.5
    Fixed in
    1.2.5

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS
8.8 · CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
EPSS
  • CVE-2026-42305: 0.64% estimated exploitation activity in the next 30 days; percentile 50.50 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

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::$INDEXALLOCATION 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,…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 2 · amended ·

    Amended from ghsa record GHSA-897w-fcg9-f6xj

  2. Revision 1 · created ·

    Published from osv record GHSA-897w-fcg9-f6xj

Agent brief

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: CVE-2026-42305

Advisory: Dulwich has an arbitrary file write via NTFS-hostile tree entries on Windows
IDs: CVE-2026-42305, GHSA-897w-fcg9-f6xj
Record: https://patchnext.com/advisories/cve-2026-42305 (revision 2, source checked 26 Oct 2026, 13:45 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.8)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: dulwich 1.2.5. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI dulwich: affected >= 0.10.0, < 1.2.5; fixed in 1.2.5

## Suggested inspection (read-only)
- `python -m pip show dulwich`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on dulwich.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-897w-fcg9-f6xj (OSV record GHSA-897w-fcg9-f6xj lists affected ranges: PyPI dulwich >=0.10.0 <1.2.5 (fixed))
- Verified: https://github.com/advisories/GHSA-897w-fcg9-f6xj (GitHub-reviewed advisory GHSA-897w-fcg9-f6xj lists affected ranges: PyPI dulwich >=0.10.0 <1.2.5)

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