Impact

Undici allows duplicate HTTP Content-Length headers when they are provided in an array with case-variant names (e.g., Content-Length and content-length). This produces malformed HTTP/1.1 requests with multiple conflicting Content-Length values on the wire.

Who is impacted: - Applications using undici.request(), undici.Client, or similar low-level APIs with headers passed as flat arrays - Applications that accept user-controlled header names without case-normalization

Potential consequences: - Denial of Service: Strict HTTP parsers (proxies, servers) will reject requests with duplicate Content-Length headers (400 Bad Request) - HTTP Request Smuggling: In deployments where an intermediary and backend interpret duplicate headers inconsistently (e.g., one uses the first value, the other uses the last), this can enable request smuggling attacks leading to ACL bypass, cache poisoning, or credential hijacking

Patches

Patched in the undici version v7.24.0 and v6.24.0. Users should upgrade to this version or later.

Workarounds

If upgrading is not immediately possible:

1. Validate header names: Ensure no duplicate Content-Length headers (case-insensitive) are present before passing headers to undici 2. Use object format: Pass headers as a plain object ({ 'content-length': '123' }) rather than an array, which naturally deduplicates by key 3. Sanitize user input: If headers originate from user input, normalize header names to lowercase and reject duplicates

A Server-Side Request Forgery (SSRF) vulnerability was found in undici, a HTTP/1.1 client for Node.js. An attacker can manipulate the server-side application to make requests to an unintended location when they use the 'path/pathname' option in 'undici.request'.

Summary

Two issues in undici's cache interceptor, both fixed by the same patch on lib/util/cache.js:

1. Shared-cache disclosure: Responses with malformed qualified Cache-Control: private directives such as private="" or private="," can be incorrectly stored in the default shared cache, then served to a later caller with the same cache key. 2. Parse-time crash: Mixed unqualified-and-qualified private directives in the same header (such as public, max-age=60, private, private="hdr") cause an uncaught TypeError in the cache-control parser, terminating the request.

Impact

Shared-cache disclosure

Applications using interceptors.cache() in shared mode may cache a user-specific response and serve it to a later caller with the same cache key. This can disclose private response bodies and headers, including Set-Cookie.

Required conditions:

- the cache interceptor is enabled in shared mode, including the default configuration; - an upstream returns a malformed directive such as Cache-Control: public, max-age=300, private=""; - another request later matches the same cache key, without a separating Vary header.

Parse-time crash

Applications using interceptors.cache() against an upstream that returns a Cache-Control header combining unqualified private with qualified private="..." see an uncaught TypeError: output.private.concat is not a function during response handling. The request rejects; depending on the consumer's error handling, the process may exit.

Details

private="" is parsed as { private: [''] }. The shared-cache guard only rejects private === true, so the response can be stored. When served from cache, the previous user's body and headers may be returned to a different user.

For the crash variant, an unqualified private directive sets output.private = true, then a subsequent qualified private="hdr" directive attempts output.private.concat(['hdr']), which throws because boolean has no concat method.

The patch routes the qualified-directive path through a shared helper that normalizes empty-after-trim arrays to true and preserves existing true values, closing both vectors.

Patches

Upgrade to undici 7.29.0 or 8.9.0. Both releases fix the qualified private directive handling that caused the shared-cache storage and the parser crash.

Workarounds

Until patched, avoid shared interceptors.cache() for user-specific responses, use type: 'private', or disable caching for affected origins.

Credit

Disclosure variant reported by @h0rk1p via HackerOne report #3817497.

Impact

undici's BalancedPool passes its constructor options through a JSON-based deep clone (JSON.parse(JSON.stringify(...))) before forwarding them to each per-upstream Pool. JSON cannot represent functions, so a caller-supplied connect or tls option containing a checkServerIdentity callback (or a custom connector function) 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 when the request is made through BalancedPool. Client, Pool, Agent, and RoundRobinPool destructure connect/tls before the clone and are not affected. Only applications that use BalancedPool with a function-valued connect/tls option (such as a custom checkServerIdentity or connector) are affected.

Patches

Upgrade to 7.29.1 or 8.10.2. BalancedPool now preserves the connect and tls options outside the JSON clone, so custom TLS verification callbacks are forwarded to each upstream unchanged.

Workarounds

Use Client, Pool, or Agent instead of BalancedPool for connections that rely on a custom checkServerIdentity or connector, until upgraded.

Impact

When an originless Agent composes the redirect and cache interceptors as compose(redirect(), cache()) with a shared cache (type: 'shared'), the cache builds its key from the original request URL before the redirect handler changes the origin. The response produced after a redirect is then stored under the original key, even when the redirect crossed to a different origin.

An attacker who controls the target of a redirect from a trusted URL can have their response cached under that trusted URL. A later caller requesting the trusted URL receives the attacker's body from the shared cache without either origin being contacted, allowing persistent cache poisoning. The same key confusion also discloses private data: when an authenticated request returns a private, no-store redirect to a user-specific resource, the final response is stored under the original URL and can be served to a later unauthenticated caller.

The cache interceptor was introduced in undici 7.0.0, and all 7.x and 8.x releases before the patched versions are affected. Applications are affected only when an originless Agent, a shared MemoryCacheStore or SqliteCacheStore, and the composition compose(redirect(), cache()) are all used. Origin-bound Client and Pool dispatchers, and the reverse composition compose(cache(), redirect()), are not affected.

Patches

Upgrade to 7.30.1 or 8.12.2. Before storing a response, undici now verifies that the origin that produced it still matches the cache key, and preserves each redirect hop's cache-control policy, so cross-origin redirect responses and responses behind a no-store or private hop are no longer cached under the original key.

Workarounds

Compose the interceptors as compose(cache(), redirect()), use per-origin dispatchers and cache stores, or disable shared caching on redirect-capable requests.

Impact

undici's Agent passes its constructor options through a JSON-based deep clone (JSON.parse(JSON.stringify(...))) before forwarding them to each per-origin Pool. JSON cannot represent functions, so 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 when the request is made through Agent. Because Agent is the default dispatcher behind request, fetch, and setGlobalDispatcher, this is the path most applications use. EnvHttpProxyAgent is also affected on its direct and NOPROXY routes, which delegate to an internal Agent.

Only applications that pass a function-valued tls option (such as a custom checkServerIdentity for certificate or public-key pinning) are affected. Passing the same options through connect is not affected. This is the Agent counterpart of the BalancedPool certificate validation bypass fixed in CVE-2026-84961.

Patches

Upgrade to undici 6.29.1, 7.30.1, or 8.12.2. Agent now preserves the tls option outside the JSON clone, so custom TLS verification callbacks are forwarded to each origin unchanged.

Workarounds

Pass the TLS options through connect instead of tls. For proxied EnvHttpProxyAgent destinations, use requestTls / proxyTls.

Impact

When using Socks5ProxyAgent, undici reuses a single connection pool across different origins without verifying that the pool's origin matches the requested origin. All requests are dispatched through the pool connected to the first origin, regardless of the intended destination.

This causes cross-origin request routing: credentials and request data intended for origin B are sent to origin A, responses from the wrong origin are trusted, and HTTPS requests may be silently downgraded to HTTP.

Impacted users are applications that use Socks5ProxyAgent (directly or via setGlobalDispatcher) and make requests to more than one origin.

This was introduced in undici 7.23.0 via #4385 and affects all versions through 8.1.0.

Patches

Upgrade to undici v7.28.0 or v8.2.0

Workarounds

Use a separate Socks5ProxyAgent instance per origin, or avoid using Socks5ProxyAgent with multiple origins.

Impact

undici's interceptors.cache() does not handle Set-Cookie in the cache path. In shared-cache mode (type: 'shared', the default), a cacheable response (for example Cache-Control: public, max-age=...) carrying a Set-Cookie header is stored, and the stored Set-Cookie is re-served to a later caller that hits the same cache key. This exposes one user's cookie to another caller and lets an untrusted upstream inject cookies into cached responses served to all subsequent callers, violating RFC 6265 section 7.2 (a shared cache must not store cookies). Applications using the shared cache interceptor against untrusted or multi-user upstreams are affected. Private caches (type: 'private') are not affected.

Patches

Upgrade to 7.29.1 or 8.10.2. In shared-cache mode, undici no longer stores or re-serves responses containing Set-Cookie, including previously cached entries and revalidation paths.

Workarounds

Use a private cache (type: 'private') for per-user responses, or avoid caching responses that set cookies. Applications acting as shared caches should strip Set-Cookie from responses before caching.

Description

Undici.ProxyAgent never verifies the remote server's certificate, and always exposes all request & response data to the proxy. This unexpectedly means that proxies can MitM all HTTPS traffic, and if the proxy's URL is HTTP then it also means that nominally HTTPS requests are actually sent via plain-text HTTP between Undici and the proxy server.

Impact

This affects all use of HTTPS via HTTP proxy using Undici.ProxyAgent with Undici or Node's global fetch. In this case, it removes all HTTPS security from all requests sent using Undici's ProxyAgent, allowing trivial MitM attacks by anybody on the network path between the client and the target server (local network users, your ISP, the proxy, the target server's ISP, etc). This less seriously affects HTTPS via HTTPS proxies. When you send HTTPS via a proxy to a remote server, the proxy can freely view or modify all HTTPS traffic unexpectedly (but only the proxy).

Patches

This issue was patched in Undici v5.5.1.

Workarounds

At the time of writing, the only workaround is to not use ProxyAgent as a dispatcher for TLS Connections.

Impact

The fetch() API supports chained HTTP encoding algorithms for response content according to RFC 9110 (e.g., Content-Encoding: gzip, br). This is also supported by the undici decompress interceptor.

However, the number of links in the decompression chain is unbounded and the default maxHeaderSize allows a malicious server to insert thousands compression steps leading to high CPU usage and excessive memory allocation.

Patches

Upgrade to 7.18.2 or 6.23.0.

Workarounds

It is possible to apply an undici interceptor and filter long Content-Encoding sequences manually.

References

https://hackerone.com/reports/3456148 https://github.com/advisories/GHSA-gm62-xv2j-4w53 https://curl.se/docs/CVE-2022-32206.html

Description

The undici WebSocket client is vulnerable to a denial-of-service attack via unbounded memory consumption during permessage-deflate decompression. When a WebSocket connection negotiates the permessage-deflate extension, the client decompresses incoming compressed frames without enforcing any limit on the decompressed data size. A malicious WebSocket server can send a small compressed frame (a "decompression bomb") that expands to an extremely large size in memory, causing the Node.js process to exhaust available memory and crash or become unresponsive.

The vulnerability exists in the PerMessageDeflate.decompress() method, which accumulates all decompressed chunks in memory and concatenates them into a single Buffer without checking whether the total size exceeds a safe threshold.

Impact

- Remote denial of service against any Node.js application using undici's WebSocket client - A single compressed WebSocket frame of ~6 MB can decompress to ~1 GB or more - Memory exhaustion occurs in native/external memory, bypassing V8 heap limits - No application-level mitigation is possible as decompression occurs before message delivery

Patches

Users should upgrade to fixed versions.

Workarounds

No workaround are possible.

Impact A server can reply with a WebSocket frame using the 64-bit length form and an extremely large length. undici's ByteParser overflows internal math, ends up in an invalid state, and throws a fatal TypeError that terminates the process.

Patches

Patched in the undici version v7.24.0 and v6.24.0. Users should upgrade to this version or later.

Workarounds

There are no workarounds.

Impact

The undici WebSocket client is vulnerable to a denial-of-service attack due to improper validation of the servermaxwindowbits parameter in the permessage-deflate extension. When a WebSocket client connects to a server, it automatically advertises support for permessage-deflate compression. A malicious server can respond with an out-of-range servermaxwindowbits value (outside zlib's valid range of 8-15). When the server subsequently sends a compressed frame, the client attempts to create a zlib InflateRaw instance with the invalid windowBits value, causing a synchronous RangeError exception that is not caught, resulting in immediate process termination.

The vulnerability exists because:

1. The isValidClientWindowBits() function only validates that the value contains ASCII digits, not that it falls within the valid range 8-15 2. The createInflateRaw() call is not wrapped in a try-catch block 3. The resulting exception propagates up through the call stack and crashes the Node.js process

Patches Has the problem been patched? What versions should users upgrade to?

Workarounds Is there a way for users to fix or remediate the vulnerability without upgrading?

Impact

The undici WebSocket client enforces maxPayloadSize on the cumulative byte count of fragments in a message but does not enforce a limit on the number of fragments. A malicious WebSocket server can stream many small or empty continuation frames that each pass per-frame and cumulative-size validation, collectively causing unbounded memory growth in the client process. The result is memory exhaustion and a denial of service.

Affected applications are those using the undici WebSocket client (new WebSocket(...)) or the WebSocketStream API that can be induced to connect to an attacker-controlled or compromised WebSocket endpoint.

All releases starting at undici 6.17.0 are affected.

Patches

Upgrade to undici v6.27.0, v7.28.0 or v8.5.0.

Workarounds

No workaround is available. The fix must be applied through an upgrade.

Impact

The undici WebSocket client enforces maxPayloadSize per-frame but does not enforce the cumulative size of fragmented uncompressed messages. A malicious WebSocket server can stream many small fragments that each pass per-frame validation but collectively exceed the configured limit, causing unbounded memory growth in the client process. The result is memory exhaustion and a denial of service.

Affected applications are those using the undici WebSocket client (new WebSocket(...)) that can be induced to connect to an attacker-controlled or compromised WebSocket endpoint.

This is a regression specific to undici 8.1.0. The 6.25.0 line shipped the equivalent cumulative check from the start and is unaffected. The 7.x line never had the maxPayloadSize feature and is also unaffected.

Patches

Upgrade to undici >= 8.5.0.

Workarounds

No workaround is available. The fix must be applied through an upgrade.

Impact

Undici's cache interceptor mishandles optional whitespace (OWS) placed around the = of a qualified no-cache or private Cache-Control directive, such as no-cache ="authorization" (OWS before =) or no-cache= "authorization" (OWS after =). The parser either drops the directive entirely or stores a field name with literal quote characters, so the downstream cache decisions do not recognize the qualification and the response is stored.

In shared-cache mode, this allows a response containing one user's authenticated data to be served from cache to a subsequent caller, including an unauthenticated caller, when both requests resolve to the same cache key. The impact class is identical to CVE-2026-9678 (GHSA-pr7r-676h-xcf6); this advisory covers the whitespace-around-= bypass that the earlier fix did not normalize.

Affected applications are those that explicitly enable the cache interceptor (interceptors.cache()) in shared mode, forward Authorization headers upstream, and receive cacheable responses with qualified private or no-cache directives whose field-name list is padded with OWS around the =.

Patches

Upgrade to undici v7.29.0 or v8.9.0.

Workarounds

If upgrade is not immediately possible, disable shared-cache mode for traffic that includes Authorization headers, avoid caching responses to authenticated requests, or add Vary: Authorization upstream.

Impact

undici's WebSocketStream crashes the client process when a WebSocket connection is closed abruptly without a close handshake. On such an unclean close, the internal socket-close handler calls abort() on the writable stream even when the application holds a writer lock. Per the WHATWG Streams standard, aborting a locked stream returns a promise that rejects with a TypeError, and the handler discards that promise. The unobserved rejection surfaces as an unhandledRejection and, under Node.js's default behavior, terminates the process.

A malicious or compromised WebSocket server can crash a client with a single connection teardown (a TCP reset, a proxy teardown, or a protocol-violating frame). Affected applications are those using the WebSocketStream API and writing through a writer, which is the standard way to write.

All releases from undici 7.0.0 are affected. WebSocketStream was introduced in 7.0.0.

Patches

Upgrade to undici v7.29.1 or v8.10.2.

Workarounds

No workaround is available.

Impact

The undici WebSocket client throws an uncaught TypeError during the opening handshake when a server's 101 response includes a Sec-WebSocket-Protocol header that the client never requested. The throw occurs in a queueMicrotask callback with no surrounding try/catch, so it propagates as an uncaught exception and terminates the Node.js process. This is a remote, unauthenticated denial of service against any application that opens a WebSocket to an attacker controlled or compromised server, or over a plaintext ws:// connection subject to a machine-in-the-middle. It affects the default new WebSocket(url) usage, where no subprotocol is requested. Per RFC 6455 section 4.1, an unrequested subprotocol must fail the connection, not crash it.

All releases starting at undici 6.7.0 are affected.

Patches

Upgrade to undici 6.28.1, 7.29.1, or 8.10.2.

Workarounds

No workaround is available. The fix must be applied through an upgrade.

Impact

undici's experimental WebSocket client (enabled by default via allowH2: true) crashes the Node.js process when it connects to a malicious server over HTTP/2. If the server answers the WebSocket upgrade with a response that fails handshake validation, undici aborts the request, but the abort is a no-op because the request is already marked completed, so the underlying ClientHttp2Stream is left open with no error listener. When the server then destroys the connection, the orphaned stream emits an unhandled error and the process exits. A remote, unauthenticated server can therefore deny service to any client that opens a WebSocket to it over HTTP/2. undici 8.11.0 and 8.11.1 are affected; the regression was introduced in 8.11.0.

Patches

Upgrade to 8.11.2.

Workarounds

Set allowH2: false to disable HTTP/2 for WebSocket connections, or avoid opening WebSocket connections to untrusted servers, until upgrading.

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.

Impact

undici's fetch() 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 (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. The early close then surfaces a content-length mismatch on that orphaned internal 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. undici 6.x, 7.x, and 8.x are affected.

Patches

Upgrade to 6.29.1, 7.30.1, or 8.12.2. undici now validates the content-encoding chain before creating the internal body stream and aborts the response when the limit is exceeded, so no error can surface on an orphaned stream.

Workarounds

None.

Impact

undici's fetch() verifies Subresource Integrity (SRI) metadata by looking up the algorithm token in a lowercase-only set, but the SRI specification defines a valid token by its ASCII-lowercase form. A correct but non-lowercase token such as SHA256-... or Sha256-... is therefore treated as unknown and skipped. When no recognized algorithm remains, undici treats the integrity list as empty and accepts the response, so a server that returns a body different from the pinned digest passes the check.

An application that pins a response with a valid uppercase or mixed-case SRI token receives attacker-controlled bytes with no integrity error. The attacker needs only to control the response body, not the application's integrity metadata. The issue affects response integrity only. The regression was introduced in undici 7.15.0; releases 7.14.0 and earlier lowercase the token and are not affected.

Patches

Upgrade to 7.30.1 or 8.12.2. undici now normalizes the algorithm token to ASCII lowercase before validating it and before selecting the strongest algorithm, so case variants of SHA-256, SHA-384, and SHA-512 are verified correctly.

Workarounds

Use lowercase algorithm tokens (sha256, sha384, sha512) in integrity metadata.

Impact

undici crashes the client process 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 ERRTLSCERTALTNAMEINVALID. undici's established socket error handler asserted that this error code could never occur, so the peer-controlled error became an uncaught AssertionError that terminates the Node.js process. Both the HTTP/1.1 and HTTP/2 paths are affected.

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. Only TLS 1.2 is affected, because TLS 1.3 does not support renegotiation. Exploitation does not require a CA compromise: the attacker controls the endpoint and can present two ordinary valid certificates, the first matching the requested URL and the second intentionally not matching it.

Patches

Upgrade to undici 6.29.1, 7.30.1, or 8.12.2.

Workarounds

Restrict outbound connections to TLS 1.3, for example by setting connect: { minVersion: 'TLSv1.3', maxVersion: 'TLSv1.3' } on the client or agent, so that renegotiation cannot occur, when the target endpoints support TLS 1.3.

Impact

undici's WebSocket client (including Node.js's bundled globalThis.WebSocket) can be driven to exhaust process memory by a malicious or compromised WebSocket server. For every PING frame received, the receiver automatically writes a PONG response to the socket and ignores the false return value from socket.write(), which is a backpressure signal, 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: small inbound PINGs produce a much larger retained outbound queue. Availability is the only impact. undici 5.x, 6.x, 7.x, and 8.x are affected; the WebSocket client was introduced in 5.15.0.

Patches

Upgrade to 6.29.1, 7.30.1, or 8.12.2, which pause WebSocket frame parsing when the automatic PONG response hits socket backpressure and resume on drain, bounding the outbound queue.

Workarounds

None.

Impact

undici's decompress interceptor forwards decompressed response data to the downstream handler from zlib stream event callbacks without catching exceptions those callbacks may throw. undici's engine converts a synchronous throw from a downstream handler into a per-request failure, but that protection is not in place when the throw happens asynchronously from a zlib callback. As a result, a downstream handler that throws by design, for example the built-in dump interceptor which throws when a response exceeds its maxSize, escapes as an uncaught exception and terminates the Node.js process.

A malicious or compromised HTTP server can crash any client that composes the decompress interceptor with dump (or another response handler that throws), by returning a small compressed body that decompresses to more than the configured limit. The compressed bytes on the wire are tiny, so only the decompressed size matters. If the application keeps the process alive with a global uncaught-exception handler, the affected request instead hangs until the body timeout.

Patches

Upgrade to undici 7.30.1 or 8.12.2.

Workarounds

Avoid composing the decompress interceptor with a response handler that throws during response processing (such as dump with a maxSize) until upgrading.

Node.js is vulnerable to a denial of service, caused by a regular expression denial of service (ReDoS) flaw in the Headers.set() and Headers.append() methods in the fetch API. By sending a specially-crafted regex input, a remote attacker could exploit this vulnerability to cause a denial of service condition.

Impact

undici's ProxyAgent silently drops the requestTls option when configured with a SOCKS5 proxy URI (socks5:// or socks://). The target HTTPS connection through the SOCKS5 tunnel falls back to Node's default trust store, ignoring user-configured ca, cert, key, rejectUnauthorized, and servername settings.

Applications that pin to an internal or corporate CA via requestTls.ca will, when their proxy URI is SOCKS5, get the default Mozilla CA bundle as the trust anchor instead. Any cert signed by any publicly-trusted CA for the target hostname is accepted, breaking the intended pin and enabling MITM read and tamper of the HTTPS exchange.

Affected applications are those that use undici's ProxyAgent (or Socks5ProxyAgent directly) with SOCKS5 AND rely on requestTls for TLS scope restriction. The bug was introduced in undici 7.23.0 when SOCKS5 support was added.

Patches

Upgrade to undici v7.28.0 or v8.5.0.

Workarounds

No workaround is available within the SOCKS5 path. If a SOCKS5 proxy with TLS scope restriction is required and an upgrade is not yet possible, route the traffic through an HTTP-proxy ProxyAgent instead, where requestTls is honored correctly.

Impact

When interceptors.cache() or interceptors.deduplicate() is used with a dispatcher that does not carry a single authoritative origin, or when a request supplies its own origin, undici builds the cache and deduplication keys without the actual destination origin. If a cache store or interceptor instance is shared across more than one origin, otherwise-identical requests to different origins are keyed together.

An attacker who controls the response from one origin can then have that response returned for a request to a different, trusted origin when the method, path, and relevant headers match. This allows cross-origin information disclosure and persistent cache poisoning, including chains such as JWKS cache poisoning where a token signed with an attacker-held key is accepted as belonging to a trusted issuer.

Applications that share interceptors.cache() or interceptors.deduplicate() state across origins are affected. An Agent is not affected, because its dispatch options include the request origin.

This was introduced in undici 8.10.0 and affects 8.10.0 and 8.10.1.

Patches

Upgrade to undici v8.10.2.

Workarounds

Use a separate cache store and a separate interceptor instance for each origin, and do not share them across origins.

Impact

Calling fetch(url) and not consuming the incoming body ((or consuming it very slowing) will lead to a memory leak.

Patches

Patched in v6.6.1

Workarounds

Make sure to always consume the incoming body.

Impact

The setCookie function has two attribute injection paths. validateCookieDomain does not reject semicolons (validateCookiePath already does at 0x3B), so a domain value like example.com; SameSite=None lands verbatim as Domain=example.com; SameSite=None. The unparsed array's loop only checks each entry contains = and does not sanitize values, so an entry like X-Custom=val; HttpOnly lands unchanged, injecting HttpOnly without the caller setting cookie.httpOnly = true.

Applications that pass user-controlled input to these fields, typically multi-tenant or reverse-proxy servers that scope session cookies to a tenant-supplied domain, can have SameSite CSRF protections bypassed, Secure or HttpOnly forced or stripped, or the intended SameSite tier overridden.

Patches

Patched in undici v6.28.0, v7.29.0, and v8.9.0.

Workarounds

- Sanitize domain values against the RFC 1034 letter-digit-hyphen set before passing to setCookie. - Do not pass user-controlled data to the unparsed field.