An issue was discovered in Pip (all versions) because it installs the version with the highest version number, even if the user had intended to obtain a private package from a private index. This only affects use of the --extra-index-url option, and exploitation requires that the package does not already exist in the public index (and thus the attacker can put the package there with an arbitrary version number). A warning was added about this behavior in version 21.1.
NOTE: it has been reported that this is intended functionality and the user is responsible for using --extra-index-url securely.

Pip 21.1 updates its dependency 'urllib3' to v1.26.4 due to security issues.

Affected versions of Pip are vulnerable to Command Injection. When installing a package from a Mercurial VCS URL (ie "pip install hg+...") with pip prior to v23.3, the specified Mercurial revision could be used to inject arbitrary configuration options to the "hg clone" call (ie "--config"). Controlling the Mercurial configuration can modify how and which repository is installed. This vulnerability does not affect users who aren't installing from Mercurial.

Affected versions of the pip package are vulnerable to Path Traversal due to an incorrect directory containment check when extracting wheel archives. In src/pip/_internal/utils/unpacking.py, the is_within_directory() helper used os.path.commonprefix() (character-by-character) to compare directory and target paths, allowing crafted paths like a parent-directory substring match to be treated as safely inside the installation directory.

A flaw was found in python-pip in the way it handled Unicode separators in git references. A remote attacker could possibly use this issue to install a different revision on a repository. The highest threat from this vulnerability is to data integrity.

Affected versions of the pip package are vulnerable to Arbitrary File Overwrite due to improper validation of symbolic link targets in the fallback tar extraction code. In src/pip/_internal/utils/unpacking.py, the _untar_without_filter routine used when the Python tarfile module lacks PEP 706 (no tarfile.data_filter) extracted symlink members with tar._extract_member without verifying that link destinations resolve under the extraction root, a check later added via the is_symlink_target_in_tar helper.

Pip solves a security vulnerability that previously allowed maliciously crafted wheel files to execute unauthorized code during installation.