isomorphic-git: Unbounded memory allocation from attacker-controlled delta target size (DoS)
Written by anthropic/claude-haiku-5.5 from the sources below. Verify against them.
- Exploited
- No known exploitation
- Fix
- Fixed in 1.38.6
- Who is exposed
- Not reported
Do first: Upgrade to a fixed version: 1.38.6.
- Exploitation?/40Exploitation: unknown (data gap). No CISA SSVC exploitation rating yet
- Exposure7/25Reachable over the network without a login · Data gap: No advisory context yet
- Reach?/20Reach: unknown (data gap). No tracked technology or package matched
- Severity4.3/10CVSS 4.3
- No patch0/5No signal
What would change the score
- Would score about 66 if added to CISA KEV
- Would score about 61 if CISA's SSVC rates exploitation active
- Would score about 26 if advisories confirm default setups are exposed
CVE-2026-63476 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 4.3 (medium) and affects isomorphic-git; fixed in 1.38.6.
- Last modified
- Where the record stands: published, rejected by its publisher, or superseded by another id.What do these mean? →
- Published
- Whether CISA lists it in its Known Exploited Vulnerabilities catalog: proof that attackers are using it.What do these mean? →
- Not listed in CISA KEV
- A 0-100 score for how much a CVE matters across the industry: exploitation, exposure, how widely the software is used, severity and whether a fix exists.What do these mean? →
- 11/100 · provisional
- Fix
- Fixed in 1.38.6
- Whether working attack code is public (Exploit-DB, Metasploit, Nuclei or GitHub). Public code makes attacks easier.What do these mean? →
- None on Exploit-DB, Metasploit or GitHub
Summary
isomorphic-git, a pure JavaScript Git implementation for Node.js and browsers, is affected. A malicious or man-in-the-middle remote can trigger an unbounded memory allocation during clone or fetch, which can exhaust memory and crash or stall the host process, such as containers, serverless functions, or small virtual machines.
Read the original description
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.
What to do
Upgrade to a fixed version: 1.38.6.
Timeline
- CVE published
- First seen by cve.now
Affected versions
- isomorphic-git isomorphic-git
fixed in 1.38.6
Evidence 4
- Advisory
- Repository
- Repository
- Repository
Corrections
None so far.
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Questions about CVE-2026-63476
Is CVE-2026-63476 being exploited?
It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.Source: cve.now feed data
Which versions are affected by CVE-2026-63476?
isomorphic-git: before 1.38.6.Source: cve.now feed data
How do I fix CVE-2026-63476?
Upgrade to a fixed version: 1.38.6.Source: cve.now feed data