undici vulnerable to Denial of Service via unbounded memory in the EventSource parser

Summary

undici is an HTTP client library for Node.js. In versions 6.5.0 through 6.29.0, 7.0.0 through 7.30.0, and 8.0.0 through 8.12.1, its EventSource client can be driven to exhaust process memory by a malicious or compromised Server-Sent Events peer. By sending millions of tiny completed data fields with no blank event separator, or a single unfinished line split across many chunks, the parser retains a growing amount of per-field and per-chunk state that the byte-based maxEventSize and maxResponseSize limits do not bound, and because maxResponseSize is enforced on the compressed body before decompression, a small compressed response can expand into enough retained memory to terminate the process. An application only needs to maintain an EventSource connection to an untrusted peer, which controls only the response, and availability is the only impact. The issue is fixed in undici 6.29.1, 7.30.1, and 8.12.2, which bound the retained parser state independently of the byte limits, and users should upgrade to one of those versions or later. There is no workaround.

Timeline

1. Oct 15, 2026, 6:16 PM UTCCVE published
2. Oct 16, 2026, 8:05 PM UTCCISA SSVC assessment

   Exploitation: none · Automatable: no · Technical impact: partial

3. Oct 16, 2026, 8:05 PM UTCRecord last updated

Affected versions

• undici undici

  From 6.5.0 · fixed in 6.29.1; From 7.0.0 · fixed in 7.30.1; From 8.0.0 · fixed in 8.12.2

• undicinpm

  From 6.5.0 · fixed in 6.29.1

• undicinpm

  From 7.0.0 · fixed in 7.30.1

• undicinpm

  From 8.0.0 · fixed in 8.12.2

References 2