GHSA-ghq2-5c67-fprm: PDM: Project-Local State and Config Writes Follow Symlinks
SummaryPDM 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.This creates an arbitrary file clobber primitive relative to the privileges of the invoking user.Affected BehaviorProject-local config writes can affect files outside the repositoryThe most stable demonstrated sink is `pdm.toml`Related sinks include `.pdm-python` and `.python-version`Affected Code`src/pdm/project/config.py:303-350``src/pdm/project/core.py:209-217``src/pdm/cli/commands/use.py:187-189`Technical Details`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.The same general problem exists for other project-local persistence paths that are written directly with no `lstat` / `O_NOFOLLOW` protection.For 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.ImpactArbitrary file clobber as the invoking userDestructive modification of local files outside the repository rootUseful primitive for privilege abuse when `pdm` is run in elevated contextsReproductionPoC:Expected result:A temporary project is created`pdm.toml` is a symlink to another TOML fileRunning `pdm config -l venv.in_project false` modifies the symlink targetObserved output from local validation:SeverityMediumCVSS v4.0Base score: `6.8` (`Medium`)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`Rationale:`AV:L`: exploitation requires local execution of `pdm` against an attacker-prepared checkout`AC:L`: there is no complex constraint once the symlink sink exists`AT:N`: no extra prerequisite beyond the victim running the relevant command is required`PR:N`: the attacker does not need prior privileges on the victim system`UI:A`: the victim must actively run a command that writes project-local state or config`VC:N`: the demonstrated issue is a write primitive, not a direct read primitive`VI:H`: the attacker can cause unauthorized modification of files outside the repository root`VA:L`: file clobber can disrupt local operation, but direct same-step availability impact is lower than a full RCE`SC:N/SI:N/SA:N`: the base score is limited to the directly affected systemRoot CauseProject-local file sinks are treated as trusted regular files and are written without symlink checks or guarded atomic replacement.Recommended RemediationRefuse to write project-local config/state files when the destination is a symlinkUse `lstat` and `O_NOFOLLOW` where availableAvoid resolving attacker-controlled project-local paths before writingUse atomic temp-file replacement only after confirming the destination is a regular fileDisclosure NotesThis 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.
CVSS v4.0: 6.8