CVE-2026-63476

isomorphic-git is a pure JavaScript implementation of Git for Node.js and browsers. Prior to 1.38.6, isomorphic-git's tree parser in src/models/GitTree.js accepts a standalone .. tree-entry name because it rejects only path separators. During clone or checkout from a malicious or man-in-the-middle-controlled non-GitHub remote, nested .. entries can escape the working-tree root and write files at attacker-selected parent paths on any host-backed fs provider. The arbitrary file write can overwrite startup or configuration files and lead to code execution. GitHub-hosted trees are not a direct source because GitHub rejects .. entries during repository integrity checks. This issue is fixed in version 1.38.6.

isomorphic-git before 1.38.6 persists server-supplied circular symref capabilities and resolves the resulting loose symbolic references without a default depth limit or cycle detection. After cloning from a malicious or man-in-the-middle-controlled remote, operations such as log, status, checkout, and branch do not terminate, leaving the repository unusable and causing a persistent denial of service.

In isomorphic-git prior to 1.38.6, git.checkout writes new child paths through symlinked leading directory components without checking them. A malicious repository can first place a directory symlink and later replace the tree state with a child file beneath that path; with Node fs on Linux or macOS the OS can resolve the write outside the working tree, permitting arbitrary host file writes and possible code execution.

isomorphic-git before 1.42.0 contains a prototype pollution vulnerability in the getRemoteInfo function. A malicious Git server operator can pollute Object.prototype by advertising crafted ref names containing '__proto__' path segments during ref negotiation.