undici vulnerable to Denial of Service via unbounded memory in the EventSource parser
CVE-2026-109924
Impact undici's 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. The byte-based maxEventSize and maxResponseSize limits do not bound that retained state, and maxResponseSize is enforced on the compressed body before decompression, so a small compressed response can expand into enough retained memory to terminate the process. The application only needs to maintain an EventSource connection to an untrusted peer, which controls only the response. Availability is the only impact. Patches Upgrade to 6.29.1, 7.30.1, or 8.12.2, which bound the retained EventSource parser state (the number of data fields and buffered chunks, the unfinished-line length, and per-field byte totals) independently of the byte limits. Workarounds None.
Assessment
- CVSS
- 5.9 (v3.1)
- Severity
- Medium
- EPSS
- 0.00321% chance of exploitation in the next 30 days
- Known exploited
- Not listed in CISA KEV
- Exploit availability
- Nothing found in Exploit-DB, Metasploit, Nuclei or public PoC repositories
- Published
- 23 October 2026
- Last updated
- 23 October 2026
- Affected
- npm · undici
- Weakness
- CWE-770
CVSS vectorCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
At the source
References
- https://github.com/nodejs/undici/security/advisories/GHSA-4qv8-2p9j-2685
- https://nvd.nist.gov/vuln/detail/CVE-2026-109924
- https://github.com/nodejs/undici/commit/299162740d5f39120092277e70efacb4d151c1c6
- https://github.com/nodejs/undici/commit/789ef26461c648480433846607154f52d74ec9ab
- https://github.com/nodejs/undici/commit/c43b23fdc6b37e1283d4347408bb16800f867d9e
- https://cna.openjsf.org/security-advisories.html
- https://github.com/nodejs/undici/releases/tag/v6.29.1
- https://github.com/nodejs/undici/releases/tag/v7.30.1
- https://github.com/nodejs/undici/releases/tag/v8.12.2
- https://github.com/advisories/GHSA-4qv8-2p9j-2685
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