---
id: CVE-2026-63476
title: >-
  isomorphic-git: Unbounded memory allocation from attacker-controlled delta
  target size (DoS)
summary: >-
  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 b…
severity: medium
cvss: 4.3
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:L'
cvssSource: cna
cwe:
  - CWE-400
  - CWE-789
vendor: isomorphic-git
product: isomorphic-git
affected:
  - isomorphic-git < 1.38.6
published: '2026-11-03'
updated: '2026-11-03'
sourceUpdated: '2026-11-03T19:44:06.908Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-63476'
references:
  - url: >-
      https://github.com/isomorphic-git/isomorphic-git/security/advisories/GHSA-9x82-4j54-863h
    label: >-
      https://github.com/isomorphic-git/isomorphic-git/security/advisories/GHSA-9x82-4j54-863h
  - url: 'https://github.com/isomorphic-git/isomorphic-git/pull/2370'
    label: 'https://github.com/isomorphic-git/isomorphic-git/pull/2370'
  - url: >-
      https://github.com/isomorphic-git/isomorphic-git/commit/823843d1cd19182df79bc907c767f5bcecb39a0b
    label: >-
      https://github.com/isomorphic-git/isomorphic-git/commit/823843d1cd19182df79bc907c767f5bcecb39a0b
  - url: 'https://github.com/isomorphic-git/isomorphic-git/releases/tag/v1.38.6'
    label: 'https://github.com/isomorphic-git/isomorphic-git/releases/tag/v1.38.6'
tags:
  - cve.org
epss: 0.00285
epssPercentile: 0.21184
ingestedAt: '2026-11-05T20:33:06.403Z'
---

## Overview

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.

## Affected

- `isomorphic-git < 1.38.6`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.