CVE-2026-119051

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.

References

• https://github.com/hughsk/flat
• https://github.com/hughsk/flat/blob/1d68e1d06c0210cff31e5c61ac177f3e2d3fa564/index.js#L137-L142
• https://github.com/hughsk/flat/blob/1d68e1d06c0210cff31e5c61ac177f3e2d3fa564/index.js#L65-L75
• https://github.com/hughsk/flat/issues/195
• https://www.vulncheck.com/advisories/flat-through-6.0.1-denial-of-service-via-unflatten-numeric-array-index-keys