Know every vulnerabilitybefore it knows you.
DevGuard continuously monitors your dependencies and alerts you when CVEs like this one affect your stack — with real-time threat intelligence built for developers.
PYSEC-2026-2463
No affected components available
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
The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker does not need any special privileges or access rights. The attacker needs the user to perform some action, like clicking a link. The impact is confined to the system where the vulnerability exists. There is a high impact on the confidentiality of the information. There is a high impact on the integrity of the data. There is a high impact on the availability of the system.
Exploitation activity has been observed. Apply available patches or mitigations urgently.
The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.
We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.
Browse More
Continuously monitor your dependencies and get alerted when vulnerabilities like this one affect your stack.
Checkout DevGuard