Is CVE-2026-63476 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-63476 being exploited in the wild.

How severe is CVE-2026-63476?

Medium severity, with a CVSS score of 4.3, published 3 November 2026.

Is there a fix for CVE-2026-63476?

Yes: fixed in 1.38.6. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

How is CVE-2026-63476 attacked?

It is attacked over the network, in a software library.

Am I affected by CVE-2026-63476?

Check whether you run Isomorphic-Git at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2026-63476: isomorphic-git unbound buffer allocation in packfile delta

CVE-2026-63476 · Severity: medium · CVSS 4.3 · Published 2026-11-03

isomorphic-git is a JavaScript implementation of Git for Node.js and browsers. Before version 1.38.6, it allocates up to 2 GB of memory without validation when a remote server sends a malicious packfile delta during git.clone() or git.fetch(). This can exhaust memory and crash containerized applications, serverless functions, and small virtual machines.

Technologies: Isomorphic-Git. Vendors: Isomorphic-Git.

Quick answers

Is CVE-2026-63476 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-63476 being exploited in the wild.
How severe is CVE-2026-63476?: Medium severity, with a CVSS score of 4.3, published 3 November 2026.
Which products and versions are affected?: Isomorphic-Git before 1.38.6.
Is there a fix for CVE-2026-63476?: Yes: fixed in 1.38.6. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-63476 attacked?: It is attacked over the network, in a software library.
Am I affected by CVE-2026-63476?: Check whether you run Isomorphic-Git at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

Fixed in: 1.38.6

Technical details

The vulnerability exists in src/utils/applyDelta.js where a server-controlled targetSize value from a delta header is passed directly to Buffer.alloc() without bounds checking. An attacker in a network position (man-in-the-middle or controlling a malicious Git server) can craft a delta with an oversized targetSize to trigger allocation of approximately 2 GB before the actual delta output is validated. The error is later silently swallowed by GitPackIndex.fromPack, allowing resource exhaustion on memory-constrained systems.

Affected products

isomorphic-git isomorphic-git before 1.38.6

Timeline

2026-11-03: disclosed
2026-07-01: patched

References

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