vulnerability / NVI-00012917 / Revision 1
Dulwich: Symlink write-through in checkout(paths=[]) via raw os.open bypasses all symlink protections
GitHub lists this reviewed advisory for dulwich. Published version ranges and source prerequisites are shown below; this is not an inspection of a visitor’s application.
This report has not inspected your inventory, configuration, deployed build, reachability or evidence. A catalog listing and a severity score do not establish exposure or compromise.
01 / Meaning
Why it matters
Published affected context helps an owner decide what evidence to gather. This report has not examined your application.
8.6 high
GitHub source severity; exploitability and local consequence require separate evidence.
As of · GitHub Advisory Database
02 / Applicability
The affected context
Affected versions, configuration prerequisites and known exclusions are public. Confirm each one against the deployed service.
dulwich
source listed>= 0.24.0, <= 1.2.7
## Summary Dulwich's `porcelain.checkout(paths=[...])` code path writes files using raw `os.open(file_path, O_WRONLY|O_CREAT|O_TRUNC, mode)` followed by `f.write(obj.data)`. This code path does NOT call `build_file_from_blob()` at all, completely bypassing any symlink protections (including the unreleased d09f8af fix). `os.open` without `O_NOFOLLOW` follows symlinks at both the target file and intermediate directories, allowing arbitrary file writes. ## Root Cause At `dulwich/porcelain/__init__.py:5661-5675`, the `checkout(paths=[...])` implementation: ```python file_path = _checked_worktree_path(r, path) os.makedirs(os.path.dirname(file_path), exist_ok=True) flags = os.O_WRONLY | os.O_CREAT | os.O_TRUNC with os.fdopen(os.open(file_path, flags, mode), "wb") as f: f.write(obj.data) ``` `_checked_worktree_path()` (line 601-631) only performs name validation — checking that the path doesn't start with `/` or `\\` and that components pass `INVALID_DOTNAMES` checks. It performs zero filesystem symlink detection. ## Impact An attacker can craft a malicious repository that, when a victim clones it and runs `checkout(paths=[...])`, writes attacker-controlled content (with attack
03 / Response
What to do next
- investigate
Identify the exact component and deployed version, examine the linked publisher’s conditions, and retain evidence of any mitigation.
Confirm current vendor support, compatibility and deployment evidence. This report has not tested a fix in your system. GitHub Advisory Database
A fixed release is not deployment evidence.
Check current vendor support and compatibility. After making a change, verify the deployed build and relevant runtime conditions. Keep the evidence, owner and time. An updated lockfile alone does not prove what is running.
04 / Limits
What this report cannot establish
- Customer inventory, deployment, reachability and exploitation have not been inspected.
05 / Provenance
Sources you can inspect
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- GHSA-8w8g-wq8h-fq33 ↗
GitHub Advisory Database · vendor advisory
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Public revision history
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- Revision 1 ·
First indexed by Null; source disclosure date is shown separately.