{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 1.2.7"
      },
      "package": {
        "ecosystem": "PyPI",
        "name": "dulwich"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0.23.1"
            },
            {
              "fixed": "1.2.8"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [],
  "database_specific": {
    "cwe_ids": [
      "CWE-22",
      "CWE-59"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-10-02T18:53:05Z",
    "nvd_published_at": null,
    "severity": "HIGH"
  },
  "details": "## Summary\n\nDulwich\u0027s `filter_branch.py` `CommitFilter._apply_index_filter()` is vulnerable to symlink directory traversal. When processing commit history, materialized tree entries (including symlinks) persist in the working directory between commits, allowing a symlink from an ancestor commit to redirect file writes from a descendant commit to arbitrary filesystem locations.\n\n## Root Cause\n\n`_apply_index_filter()` at `dulwich/filter_branch.py:212` calls `build_index_from_tree(\".\", tmp_index_path, ...)` which materializes all tree entries to the current working directory. The `finally` block (line 229-230) only cleans up the temporary index file (`os.unlink(tmp_index_path)`) \u2014 NOT the filesystem files written to CWD. When `process_commit()` processes parents recursively first (line 260), files materialized from ancestor commits persist and affect processing of descendant commits.\n\nOn dulwich 1.2.7, `build_file_from_blob()` has no symlink protection, and `validate_path_element` only validates name patterns, not filesystem state.\n\n## Impact\n\nAn attacker can craft a malicious repository where running `filter_branch` with an index filter writes attacker-controlled content to arbitrary filesystem locations via symlink traversal. This achieves RCE if the write targets `.git/hooks/`.\n\n## Attack Scenario\n\n1. Attacker creates a repository where commit history (linearized) has:\n   - Ancestor commit: tree entry `evil` (mode 120000, symlink \u2192 `/target_dir`)\n   - Descendant commit: tree entry `evil/payload` (mode 100644, attacker content)\n2. Victim clones repository and runs `filter_branch` with an index filter\n3. `process_commit()` processes ancestor first \u2192 materializes `evil` as symlink to `/target_dir` in CWD\n4. CWD is NOT cleaned between commits\n5. Processing descendant: `os.path.exists(\"./evil\")` \u2192 True (symlink exists). `build_file_from_blob(blob, mode, \"./evil/payload\")` \u2192 `open(\"./evil/payload\", \"wb\")` follows intermediate symlink \u2192 writes to `/target_dir/payload`\n\n## Suggested Fix\n\nClean the CWD between commit iterations in `_apply_index_filter()`, or verify that no intermediate path components are symlinks before writing files.\n\nReported by **zx (Jace)**",
  "id": "GHSA-5fqc-mrg8-w798",
  "modified": "2026-10-02T18:53:05Z",
  "published": "2026-10-02T18:53:05Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/jelmer/dulwich/security/advisories/GHSA-5fqc-mrg8-w798"
    },
    {
      "type": "WEB",
      "url": "https://github.com/jelmer/dulwich/commit/9571ac60b851fce228dae7ededb380c6ce9b3fb8"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/jelmer/dulwich"
    },
    {
      "type": "WEB",
      "url": "https://github.com/jelmer/dulwich/releases/tag/dulwich-1.2.8"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Dulwich: Symlink directory traversal in filter-branch index_filter via cross-commit state persistence"
}