isomorphic-git up to 1.38.5 Packfile Delta Application src/utils/applyDelta.js GitPackIndex.fromPack targetSize allocation of resources

Summaryinfo

A vulnerability, which was classified as problematic, was found in isomorphic-git up to 1.38.5. This issue affects the function GitPackIndex.fromPack of the file src/utils/applyDelta.js of the component Packfile Delta Application. Such manipulation of the argument targetSize leads to allocation of resources. This vulnerability is traded as CVE-2026-63476. The attack may be launched remotely. There is no exploit available. You should upgrade the affected component.

Detailsinfo

A vulnerability, which was classified as problematic, has been found in isomorphic-git up to 1.38.5. Affected by this issue is the function GitPackIndex.fromPack of the file src/utils/applyDelta.js of the component Packfile Delta Application. The manipulation of the argument targetSize with an unknown input leads to a allocation of resources vulnerability. Using CWE to declare the problem leads to CWE-770. The product allocates a reusable resource or group of resources on behalf of an actor without imposing any restrictions on the size or number of resources that can be allocated, in violation of the intended security policy for that actor. Impacted is availability. CVE summarizes:

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.

The advisory is shared for download at github.com. This vulnerability is handled as CVE-2026-63476 since 07/16/2026. The exploitation is known to be easy. The attack may be launched remotely. No form of authentication is required for exploitation. Successful exploitation requires user interaction by the victim. There are known technical details, but no exploit is available. The MITRE ATT&CK project declares the attack technique as T1499.

Upgrading to version 1.38.6 eliminates this vulnerability.

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Productinfo

Type

• Versioning Software

Name

• isomorphic-git

Version

• 1.38.0
• 1.38.1
• 1.38.2
• 1.38.3
• 1.38.4
• 1.38.5

Website

• Product: https://github.com/isomorphic-git/isomorphic-git/

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