CVE-2026-63476
Dashboard / Vulnerabilities / CVE-2026-63476
Summary: isomorphic-git: Unbounded memory allocation from attacker-controlled delta target size (DoS)
Details: 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.
References: https://github.com/isomorphic-git/isomorphic-git/releases/tag/v1.38.6, https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/63xxx/CVE-2026-63476.json, https://github.com/isomorphic-git/isomorphic-git/security/advisories/GHSA-9x82-4j54-863h, https://nvd.nist.gov/vuln/detail/CVE-2026-63476, https://github.com/isomorphic-git/isomorphic-git/commit/823843d1cd19182df79bc907c767f5bcecb39a0b, https://github.com/isomorphic-git/isomorphic-git/pull/2370
Affected packages
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