undici is an HTTP client library for Node.js. In versions 4.2.1 through 6.29.0, 7.0.0 through 7.30.0, and 8.0.0 through 8.12.1, the client process crashes when a TLS 1.2 server renegotiates after the connection is established and presents a different, CA-trusted certificate whose hostname does not match the requested host. Node.js re-runs hostname verification on the renegotiated handshake and destroys the socket with a certificate-altname error, but undici's established-socket error handler asserted that this error code could never occur, so the peer-controlled error became an uncaught assertion that terminates the Node.js process, affecting both the HTTP/1.1 and HTTP/2 paths. A malicious or compromised HTTPS endpoint reached through undici or the global fetch() can crash the client with a single server-initiated renegotiation, taking down all in-flight requests and background work in the process, and exploitation needs no CA compromise because the attacker controls the endpoint and can present two ordinary valid certificates. Only TLS 1.2 is affected, since TLS 1.3 does not support renegotiation. The issue is fixed in undici 6.29.1, 7.30.1, and 8.12.2, and users should upgrade to one of those versions or later. As a workaround, restrict outbound connections to TLS 1.3 so renegotiation cannot occur, when the target endpoints support it.
CVSS Score
7.5
EPSS Score
0.002
Published
2026-10-15
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.
CVSS Score
5.9
EPSS Score
0.003
Published
2026-10-15
undici is an HTTP client library for Node.js. In versions 5.15.0 through 6.29.0, 7.0.0 through 7.30.0, and 8.0.0 through 8.12.1, its WebSocket client, including the bundled WebSocket exposed by Node.js, can be driven to exhaust process memory by a malicious or compromised WebSocket server. For every PING frame received, the client automatically writes a PONG response and ignores the backpressure signal from the socket write, so a server that streams small PING frames while never reading the client's PONGs makes the outbound write queue and heap grow without bound until the Node.js process runs out of memory and terminates. The attack is remote and unauthenticated, needs only a normal WebSocket connection, and is asymmetric, since small inbound PINGs produce a much larger retained outbound queue, with availability the only impact. The issue is fixed in undici 6.29.1, 7.30.1, and 8.12.2, which pause WebSocket frame parsing when the automatic PONG response hits socket backpressure and resume on drain, bounding the outbound queue, and users should upgrade to one of those versions or later. There is no workaround.
CVSS Score
5.9
EPSS Score
0.003
Published
2026-10-15
undici is an HTTP client library for Node.js. In versions 6.23.0 through 6.29.0, 7.18.0 through 7.30.0, and 8.0.0 through 8.12.1, its fetch() implementation crashes the Node.js process when a malicious server returns a response with more than five content codings and closes the connection before sending the body. undici rejects such responses because of a content-encoding limit, but it created the internal response stream before that check and returned without attaching an error listener or aborting the request, so the early close surfaces a content-length mismatch on the orphaned stream, which Node.js treats as an unhandled error and terminates the process. A remote, unauthenticated server can trigger this with a single response, even when the application correctly catches the fetch() rejection, resulting in a denial of service. The issue is fixed in undici 6.29.1, 7.30.1, and 8.12.2, and users should upgrade to one of those versions or later. There is no workaround.
CVSS Score
7.5
EPSS Score
0.003
Published
2026-10-15
undici is an HTTP client library for Node.js. In versions 4.0.0 through 6.29.0, 7.0.0 through 7.30.0, and 8.0.0 through 8.12.1, its Agent dispatcher passes its constructor options through a JSON-based deep clone before forwarding them to each per-origin pool, and because JSON cannot represent functions, a caller-supplied tls option containing a checkServerIdentity callback is silently dropped before it reaches the TLS layer. As a result, a TLS peer whose certificate a custom checkServerIdentity was written to reject, but which passes Node's default hostname and chain checks, is silently accepted. Because Agent is the default dispatcher behind request, fetch, and setGlobalDispatcher, this affects the path most applications use, and EnvHttpProxyAgent is affected on its direct and no-proxy routes as well, while only applications that pass a function-valued tls option such as a custom checkServerIdentity for certificate or public-key pinning are at risk. The issue is fixed in undici 6.29.1, 7.30.1, and 8.12.2, which preserve the tls option outside the JSON clone so custom verification callbacks are forwarded unchanged, and users should upgrade to one of those versions or later. As a workaround, pass the TLS options through connect instead of tls, or for proxied destinations use requestTls and proxyTls.
CVSS Score
7.4
EPSS Score
0.002
Published
2026-10-15