undici's experimental WebSocketStream client crashes the whole Node.js process when a remote peer closes the TCP connection without a WebSocket close handshake. On an unclean close the internal socket-close handler calls abort on the writable stream unconditionally and discards the returned promise, but per the WHATWG Streams standard aborting a locked writable returns a promise that rejects with a TypeError. Because the application holds a writer on that writable, which is the only way to write, the rejection is never observed and Node's default unhandled-rejection behavior terminates the process. An untrusted server can therefore crash a client with a single abrupt disconnect, with no authentication and no application mistake. This affects undici versions from 7.0.0 up to 7.29.1 and from 8.0.0 up to 8.10.2. Users should upgrade to undici 7.29.1 or 8.10.2.
undici's decompress interceptor decompresses response bodies according to the untrusted Content-Encoding header. While the number of content-encoding layers is capped, the total decompressed output size is unbounded and there is no configuration option to limit it. A malicious or faulty upstream can therefore return a small compressed payload, a compression bomb, that expands to hundreds of megabytes or more in client memory, an asymmetric resource consumption that can exhaust memory and crash the process. This affects undici versions from 7.15.0 up to 7.29.1 and from 8.0.0 up to 8.10.2. Users should upgrade to undici 7.29.1 or 8.10.2.
undici's WebSocket client crashes the whole Node.js process during the opening handshake when a server responds with a subprotocol that the client never requested. A default WebSocket connection sends no subprotocol, but if the server's 101 response includes a Sec-WebSocket-Protocol header, undici dereferences a null value while checking it against the requested list and throws an uncaught TypeError. Because that code runs inside a microtask with no surrounding error handling, the exception propagates and terminates the process under Node's default behavior, instead of gracefully failing the connection as required by the WebSocket protocol. Any application that opens a WebSocket to an attacker-controlled or compromised server, or over a plaintext connection subject to a machine-in-the-middle, can be crashed remotely without authentication in the default configuration. This affects undici versions from 6.7.0 up to 6.28.1, from 7.0.0 up to 7.29.1, and from 8.0.0 up to 8.10.2. Users should upgrade to undici 6.28.1, 7.29.1, or 8.10.2.
undici's retry interceptor can append the body of a ranged retry response to bytes already delivered from an earlier partial response while still presenting the original response's status and headers. This happens when an upstream server delivers part of a body without a trustworthy resume checkpoint, for example a non-success response whose headers were already sent or a partial-content response with an unusable content range, then closes the connection and answers the resumed range request with more bytes. As a result the response body can be longer than the Content-Length that the application observes. An application that relays such a response to a downstream HTTP/1.1 peer without normalizing the framing can emit a body that exceeds the forwarded Content-Length, and the excess bytes can be interpreted as the start of a following response, which enables downstream response splitting or desynchronization. Exploitation requires an attacker-controlled upstream server and an application that forwards the response through a framing-sensitive path. This affects undici versions before 6.28.1, from 7.0.0 up to 7.29.1, and from 8.0.0 up to 8.10.2. Users should upgrade to undici 6.28.1, 7.29.1, or 8.10.2.
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 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
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 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.
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
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
undici's cookie parser in parseSetCookie percent-decodes cookie values via qsUnescape, turning encoded sequences like %0D%0A, %00, %3B, and %3D into their literal byte equivalents. RFC 6265 §5.4 does not specify any decoding and browsers do not decode either.
Applications that parse a Set-Cookie header and then forward the parsed value into a response header (proxies, middleware, SSR frameworks) become vulnerable to HTTP response header injection: an attacker-controlled upstream can inject arbitrary Set-Cookie, Location, or Cache-Control headers into the application's downstream response, enabling session fixation, open redirect, or cache poisoning.
Affected applications are those that use undici's cookie parsing (parseSetCookie, parseCookie, getSetCookies) and forward the parsed cookie value into a response header.
This was introduced in undici 7.0.0 via #3789.
Patches
Upgrade to undici v6.27.0, v7.28.0 or v8.5.0.
Workarounds
If upgrade is not immediately possible, do not forward values returned by parseSetCookie/parseCookie/getSetCookies directly into response headers; sanitize the value first to strip or reject CR, LF, NUL, ;, and = bytes.
Impact
When undici parses a Set-Cookie header, it accepts any SameSite attribute value that contains Strict, Lax, or None as a substring, rather than the case-insensitive exact match specified by RFC 6265. Non-spec values are silently mapped to one of the three standard tokens:
- SameSite=NoneOfYourBusiness is parsed as None, the most permissive setting. - SameSite=StrictLax is parsed as Lax, a downgrade from Strict.
Affected applications are those that consume Set-Cookie headers from server responses (for example via undici's fetch or proxy code paths) and then forward or rely on the parsed sameSite attribute. A malicious or non-compliant server can coerce the consumer's view of a cookie's SameSite policy to a weaker value, silently degrading the SameSite enforcement the cookie is supposed to provide.
This was introduced in undici 5.15.0 when the cookies feature was added.
Patches
Upgrade to undici v6.27.0, v7.28.0 or v8.5.0.
Workarounds
After parsing a Set-Cookie header, validate that the resulting sameSite attribute is one of 'Strict', 'Lax', or 'None' (exact, case-insensitive) before forwarding or relying on it.
Impact
Undici's HTTP/1.1 client is vulnerable to response queue poisoning on reused keep-alive sockets. An attacker-controlled upstream server can inject an unsolicited HTTP/1.1 response onto an idle socket after a request completes. When the client dispatches the next request on that socket, it associates the injected response with the new request, causing responses to be delivered to the wrong requests.
This requires an attacker-controlled or compromised upstream HTTP/1.1 server and keep-alive connection reuse.
Patches
Upgrade to undici v6.27.0, v7.28.0 or v8.5.0.
Workarounds
Disable keep-alive connection reuse by setting keepAliveTimeout: 0 on the Client or Pool.
Impact
Undici's cache interceptor incorrectly classifies some responses as cacheable when the upstream Cache-Control header uses whitespace-padded qualified private or no-cache field names such as private=" authorization" or no-cache="\tauthorization". The parser preserves the surrounding whitespace, so later comparisons against the literal authorization field name fail 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.
Affected applications are those that explicitly enable the cache interceptor (interceptors.cache()) in shared mode, forward Authorization headers upstream, and receive cacheable responses with non-canonical qualified private or no-cache directives.
Patches
Upgrade to undici v7.28.0 or v8.5.0.
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 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
Impact This is an uncontrolled resource consumption vulnerability (CWE-400) that can lead to Denial of Service (DoS).
In vulnerable Undici versions, when interceptors.deduplicate() is enabled, response data for deduplicated requests could be accumulated in memory for downstream handlers. An attacker-controlled or untrusted upstream endpoint can exploit this with large/chunked responses and concurrent identical requests, causing high memory usage and potential OOM process termination.
Impacted users are applications that use Undici’s deduplication interceptor against endpoints that may produce large or long-lived response bodies.
Patches
The issue has been patched by changing deduplication behavior to stream response chunks to downstream handlers as they arrive (instead of full-body accumulation), and by preventing late deduplication when body streaming has already started.
Users should upgrade to the first official Undici (and Node.js, where applicable) releases that include this patch.
Workarounds If upgrading immediately is not possible:
- Disable interceptors.deduplicate() for affected clients/routes. - Use skipHeaderNames with a marker header to force high-risk requests to bypass deduplication. - Avoid concurrent identical requests to untrusted endpoints that may return very large/chunked bodies. - Apply upstream/proxy response-size and timeout limits.
Impact
When an application passes user-controlled input to the upgrade option of client.request(), an attacker can inject CRLF sequences (\r\n) to:
1. Inject arbitrary HTTP headers 2. Terminate the HTTP request prematurely and smuggle raw data to non-HTTP services (Redis, Memcached, Elasticsearch)
The vulnerability exists because undici writes the upgrade value directly to the socket without validating for invalid header characters:
javascript // lib/dispatcher/client-h1.js:1121 if (upgrade) { header += connection: upgrade\r\nupgrade: ${upgrade}\r\n }
Patches
Patched in the undici version v7.24.0 and v6.24.0. Users should upgrade to this version or later.
Workarounds
Sanitize the upgrade option string before passing to undici:
javascript function sanitizeUpgrade(value) { if (/[\r\n]/.test(value)) { throw new Error('Invalid upgrade value') } return value }
client.request({ upgrade: sanitizeUpgrade(userInput) })
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.
ImpactWhen an application passes user-controlled input to the upgrade option of client.request(), an attacker can inject CRLF sequences (\r\n) to:
Inject arbitrary HTTP headers Terminate the HTTP request prematurely and smuggle raw data to non-HTTP services (Redis, Memcached, Elasticsearch) The vulnerability exists because undici writes the upgrade value directly to the socket without validating for invalid header characters:
// lib/dispatcher/client-h1.js:1121 if (upgrade) { header += connection: upgrade\r\nupgrade: ${upgrade}\r\n }
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
ImpactA 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.
ImpactThe 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:
The isValidClientWindowBits() function only validates that the value contains ASCII digits, not that it falls within the valid range 8-15 The createInflateRaw() call is not wrapped in a try-catch block The resulting exception propagates up through the call stack and crashes the Node.js process
This is an uncontrolled resource consumption vulnerability (CWE-400) that can lead to Denial of Service (DoS).
In vulnerable Undici versions, when interceptors.deduplicate() is enabled, response data for deduplicated requests could be accumulated in memory for downstream handlers. An attacker-controlled or untrusted upstream endpoint can exploit this with large/chunked responses and concurrent identical requests, causing high memory usage and potential OOM process termination.
Impacted users are applications that use Undici’s deduplication interceptor against endpoints that may produce large or long-lived response bodies.
PatchesThe issue has been patched by changing deduplication behavior to stream response chunks to downstream handlers as they arrive (instead of full-body accumulation), and by preventing late deduplication when body streaming has already started.
Users should upgrade to the first official Undici (and Node.js, where applicable) releases that include this patch.
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: 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 >= 6.26.0, >= 7.28.0, or >= 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.
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 interceptors.retry() can deliver a response whose body length does not match the Content-Length header exposed to the application after a retry or resume of a partial response. Applications that use interceptors.retry() and forward upstream response headers and bodies downstream, for example proxy or gateway applications, may emit an invalid HTTP response with a stale Content-Length header. This can lead to downstream response desynchronization, connection hangs, or response corruption in clients or intermediaries that rely on the forwarded framing metadata.
A malicious or faulty upstream can respond to a range request with a 206 Partial Content response such as:
http Content-Range: bytes 0-99/300 Content-Length: 300
and then send only 99 bytes before closing the socket. interceptors.retry() can then retry with Range: bytes=99-99, receive the final byte, and deliver a 100-byte body to the application while the response headers still contain Content-Length: 300 from the first response.
The bug requires interceptors.retry() to be enabled, an upstream that returns a partial response with a mismatched framing header, and a downstream forwarder that does not remove or recalculate Content-Length.
Patches
Patched in undici v6.28.0, v7.29.0, and v8.9.0. Users should upgrade to one of these versions or later.
Workarounds
- Disable interceptors.retry() for untrusted upstreams. - Remove or recalculate Content-Length before forwarding a response body assembled or transformed by Undici.
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 PR #4385 and affects all versions through 8.1.0.
Patches: Upgrade to undici v7.26.0 or v8.2.0.
Workarounds: Use a separate Socks5ProxyAgent instance per origin, or avoid using Socks5ProxyAgent with multiple origins.
Impact: Undici's cache interceptor incorrectly classifies some responses as cacheable when the upstream Cache-Control header uses whitespace-padded qualified private or no-cache field names such as private=" authorization" or no-cache="\tauthorization". The parser preserves the surrounding whitespace, so later comparisons against the literal authorization field name fail 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.
Affected applications are those that explicitly enable the cache interceptor (interceptors.cache()) in shared mode, forward Authorization headers upstream, and receive cacheable responses with non-canonical qualified private or no-cache directives.
Patches: Upgrade to undici v7.28.0 or v8.5.0.
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.