CVE-2026-47763: PDM Project-Local State And Config Writes Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-ghq2-5c67-fprm",
  "modified" : "2026-06-10T20:32:56Z",
  "published" : "2026-06-10T20:32:56Z",
  "aliases" : [ "CVE-2026-47763" ],
  "summary" : "PDM: Project-Local State and Config Writes Follow Symlinks",
  "details" : "## Summary\n\nPDM writes several project-local state or configuration files without symlink protection. If a malicious repository places those files as symlinks, local PDM operations can overwrite the symlink targets.\n\nThis creates an arbitrary file clobber primitive relative to the privileges of the invoking user.\n\n## Affected Behavior\n\n- Project-local config writes can affect files outside the repository\n- The most stable demonstrated sink is `pdm.toml`\n- Related sinks include `.pdm-python` and `.python-version`\n\n## Affected Code\n\n- `src/pdm/project/config.py:303-350`\n- `src/pdm/project/core.py:209-217`\n- `src/pdm/cli/commands/use.py:187-189`\n\n## Technical Details\n\n`Config.__init__()` resolves the project-local `pdm.toml` path and `_save_config()` writes to the resolved target. If `PROJECT_ROOT/pdm.toml` is a symlink to another file, `pdm config -l ...` updates the target file instead of refusing the write.\n\nThe same general problem exists for other project-local persistence paths that are written directly with no `lstat` / `O_NOFOLLOW` protection.\n\nFor the `pdm.toml` PoC specifically, the target file must already contain parseable TOML. Otherwise the load step fails before the write path is reached. That parser constraint does not apply to the `.pdm-python` or `.python-version` sinks.\n\n## Impact\n\n- Arbitrary file clobber as the invoking user\n- Destructive modification of local files outside the repository root\n- Useful primitive for privilege abuse when `pdm` is run in elevated contexts\n\n## Reproduction\n\nPoC:\n\n```bash\n# Replace this with a Python interpreter that can run `python -m pdm`.\nPDM_PY=/path/to/python-with-pdm\ntmpdir=$(mktemp -d)\ntarget=\"$tmpdir/clobbered-target.toml\"\n\ncat > \"$target\" <<'EOF'\n[seed]\nvalue = 1\nEOF\n\nln -s \"$target\" \"$tmpdir/pdm.toml\"\n\ncat > \"$tmpdir/pyproject.toml\" <<'EOF'\n[project]\nname = \"symlink-clobber-demo\"\nversion = \"0.0.1\"\nEOF\n\n(\n  cd \"$tmpdir\" &&\n  \"$PDM_PY\" -m pdm config -l venv.in_project false\n)\n\ncat \"$target\"\n```\n\nExpected result:\n\n- A temporary project is created\n- `pdm.toml` is a symlink to another TOML file\n- Running `pdm config -l venv.in_project false` modifies the symlink target\n\nObserved output from local validation:\n\n```text\n--- target ---\n[seed]\nvalue = 1\n\n[venv]\nin_project = false\n```\n\n## Severity\n\nMedium\n\n## CVSS v4.0\n\n- Base score: `6.8` (`Medium`)\n- Vector: `CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:A/VC:N/VI:H/VA:L/SC:N/SI:N/SA:N`\n\nRationale:\n\n- `AV:L`: exploitation requires local execution of `pdm` against an attacker-prepared checkout\n- `AC:L`: there is no complex constraint once the symlink sink exists\n- `AT:N`: no extra prerequisite beyond the victim running the relevant command is required\n- `PR:N`: the attacker does not need prior privileges on the victim system\n- `UI:A`: the victim must actively run a command that writes project-local state or config\n- `VC:N`: the demonstrated issue is a write primitive, not a direct read primitive\n- `VI:H`: the attacker can cause unauthorized modification of files outside the repository root\n- `VA:L`: file clobber can disrupt local operation, but direct same-step availability impact is lower than a full RCE\n- `SC:N/SI:N/SA:N`: the base score is limited to the directly affected system\n\n## Root Cause\n\nProject-local file sinks are treated as trusted regular files and are written without symlink checks or guarded atomic replacement.\n\n## Recommended Remediation\n\n- Refuse to write project-local config/state files when the destination is a symlink\n- Use `lstat` and `O_NOFOLLOW` where available\n- Avoid resolving attacker-controlled project-local paths before writing\n- Use atomic temp-file replacement only after confirming the destination is a regular file\n\n## Disclosure Notes\n\nThis issue is independent from the code-execution issues above. It is best tracked as a separate CVE candidate because the root cause and remediation are different.",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:A/VC:N/VI:H/VA:L/SC:N/SI:N/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "pdm"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "2.27.0"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/pdm-project/pdm/security/advisories/GHSA-ghq2-5c67-fprm"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/pdm-project/pdm"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/pdm-project/pdm/releases/tag/2.27.0"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-61" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-06-10T20:32:56Z",
    "nvd_published_at" : null
  }
}