{"id":"CVE-2026-114097","aliases":["GHSA-5fqc-mrg8-w798"],"url":"https://o3.security/vulnerability/CVE-2026-114097","summary":"Dulwich 0.23.1 before 1.2.8 Symlink Path Traversal via filter_branch Index Filter","details":"## Summary\n\nDulwich's `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)`) — 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 → `/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 → materializes `evil` as symlink to `/target_dir` in CWD\n4. CWD is NOT cleaned between commits\n5. Processing descendant: `os.path.exists(\"./evil\")` → True (symlink exists). `build_file_from_blob(blob, mode, \"./evil/payload\")` → `open(\"./evil/payload\", \"wb\")` follows intermediate symlink → 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)**","published":"2026-10-21T00:37:00.461Z","modified":"2026-10-21T10:45:32.502788327Z","cvss":null,"epss":null,"cisaKev":null,"exploitsKnown":null,"affectedPackages":[{"ecosystem":"PyPI","name":"dulwich","fixedVersion":"1.2.8"}],"fix":{"url":"https://github.com/jelmer/dulwich/commit/9571ac60b851fce228dae7ededb380c6ce9b3fb8","label":"jelmer/dulwich@9571ac6"},"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/114xxx/CVE-2026-114097.json"},{"type":"ADVISORY","url":"https://github.com/jelmer/dulwich/security/advisories/GHSA-5fqc-mrg8-w798"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-114097"},{"type":"ADVISORY","url":"https://www.vulncheck.com/advisories/dulwich-0.23.1-before-1.2.8-symlink-path-traversal-via-filter-branch-index-filter"},{"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"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-10-21T10:45:32.502788327Z"}}