# CVE-2026-63476: isomorphic-git: Unbounded memory allocation from attacker-controlled delta target size (DoS)

Status: published. Published: 2026-11-03. Updated: 2026-11-03.

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.

## Remediation

No remediation reported in collected sources

## Affected products and versions

- isomorphic-git / isomorphic-git: < 1.38.6 (affected). Source: CNA: GitHub_M

## Severity and prioritization

- CVSS 3.1: 4.3 (medium); CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:L; source: CNA: GitHub_M

- CISA KEV: No listing in collected sources

- EPSS: Not available

- SSVC: Not available

- Weaknesses: CWE-400, CWE-789

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://github.com/isomorphic-git/isomorphic-git/security/advisories/GHSA-9x82-4j54-863h (CNA: GitHub_M; x_refsource_CONFIRM)

- https://github.com/isomorphic-git/isomorphic-git/pull/2370 (CNA: GitHub_M; x_refsource_MISC)

- https://github.com/isomorphic-git/isomorphic-git/commit/823843d1cd19182df79bc907c767f5bcecb39a0b (CNA: GitHub_M; x_refsource_MISC)

- https://github.com/isomorphic-git/isomorphic-git/releases/tag/v1.38.6 (CNA: GitHub_M; x_refsource_MISC)

## Provenance

- CNA: GitHub_M: https://www.cve.org/CVERecord?id=CVE-2026-63476; retrieved 2026-11-03; source updated 2026-11-03

Revision: ea8b42acba0fbde747b13058837a4c8703204956f37516b9e5d74b7f2896ad6a

Canonical: https://y2.dev/cve/CVE-2026-63476

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