NIST deprecates RSA-2048 from 2030. Find every one of them before attackers do.
🐍 PyPI
Not in CISA KEV

CVE-2026-42563 — dulwich

Fix: jelmer/dulwich@e3331b3

CVE-2026-42563 is a OS Command Injection vulnerability in dulwich. A fix is available for dulwich — see the affected versions and patch details below.

Dulwich Vulnerable to Command Injection via Merge Driver Path

Also known asGHSA-9277-mp7x-85jfPYSEC-2026-2464
Published
Updated
Affected
1 pkg
Patched
1 / 1
Exploits
None indexed
Exploitation data as of Nov 11, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

Proof-of-concept exploit code exists

  • CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
  • A successful exploit gives an attacker total control of the affected component, not partial access.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-42563.

EPSS Exploitation Probability

via FIRST.org ↗
0.6%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs47th percentile — riskier than 47% of all scored CVEsHighest risk
0.06%0.47%0.88%1.30%0.6%0.6%Jul 26Oct 26Nov 26

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

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

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

Proof of Concept

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

Affected Packages

1 total 1 fixed
EcosystemPackageVulnerable rangeFix
🐍PyPIdulwich≥ 0.24.0&&< 1.2.51.2.5pip install --upgrade 'dulwich==1.2.5'

Detection & mitigation playbook

Open-source dependency

  1. 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.

  2. Fix

    Update dulwich to 1.2.5 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-42563 is resolved across your whole dependency graph.

  3. Workarounds

    Stop passing untrusted input into the interpreter or shell: call the affected binary with an argument array rather than a composed command string, reject anything outside a strict allowlist of expected values, and run the component under an account that cannot reach beyond the work it legitimately does.

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 command injection flaw in Dulwich, a Git file format and protocol implementation. The vulnerability allows arbitrary code execution when a user merges a malicious Git branch, provided a merge driver is configured to use the %P placeholder. This elevates the risk to Important due to the potential…

Workaround published by Red Hat
Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base, or stability.
Source: Red Hat security advisory for CVE-2026-42563 (CC BY 4.0)

Frequently Asked Questions

## 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 — `su
O3 Security · Impact-Aware SCA

Is CVE-2026-42563 in your dependencies?

Find it across PyPI, including transitive dependencies.

Scan my dependencies How O3 SCA works
CVE-2026-42563: dulwich RCE — Fixed in 1.2.5