Vulnerability · Published Oct 29, 2026 · Assigned by VulnCheck
CVE-2026-119051flat through 6.0.1 Denial of Service via unflatten() Numeric Array Index Keys
Medium 5.9
In plain English
A medium-severity resource allocation without limits in flat from hughsk. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 25% of all known vulnerabilities).
Severity (CVSS 3.1)5.9Medium
Exploit odds (30 days)0.3%top 74.9% of all CVEs
Exploited in the wildNo reportsCISA SSVC: poc
Attack toolingNoneno public tooling known
Official description
flat through 6.0.1 contains an uncontrolled resource allocation vulnerability in unflatten() that allows attackers to create huge sparse arrays via unbounded numeric keys. Attackers can supply flattened keys such as a.4294967294, causing iteration with forEach, spread or JSON.stringify to block the Node.js event loop.
Affected products (as reported)
Weakness: CWE-770 · Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
References
- GitHub Issue #195 issue-tracking
- https://github.com/hughsk/flat product
- https://github.com/hughsk/flat/blob/1d68e1d06c0210cff31e5c61ac177f3e2d3fa564/index.js#L65-L75 technical-description
- https://github.com/hughsk/flat/blob/1d68e1d06c0210cff31e5c61ac177f3e2d3fa564/index.js#L137-L142 technical-description
- VulnCheck Advisory: flat through 6.0.1 Denial of Service via unflatten() Numeric Array Index Keys third-party-advisory