CVE-2026-63478

isomorphic-git is a pure JavaScript implementation of Git for Node.js and browsers. Prior to 1.38.6, isomorphic-git reads a server-controlled targetSize while applying a packfile delta in src/utils/applyDelta.js and passes it without a bound to Buffer.alloc(targetSize). A malicious or man-in-the-middle-controlled remote can send one delta header that causes git.clone() or git.fetch() to allocate approximately 2 GB before validating the actual delta output. GitPackIndex.fromPack swallows the later size-mismatch error, so a host with sufficient memory may retain the resource waste without a visible failure, while containers, serverless functions, and small virtual machines may terminate. Node.js heap limits do not mitigate the off-heap Buffer allocation. 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.