Security fixes
High severity
Denial of service via TLS 1.2 certificate-changing renegotiation
CVE-2026-87018 · GHSA-qrxm-fqhp-jwvm
A malicious or compromised HTTPS server could crash the Node.js process by initiating TLS 1.2 renegotiation and presenting a different, CA-trusted certificate whose hostname did not match the requested host. The resulting socket error reached an assertion in undici's HTTP/1.1 and HTTP/2 connection handling. This release handles post-connect certificate errors without terminating the process.
TLS certificate validation bypass through dropped Agent options
CVE-2026-109383 · GHSA-2m5v-pch6-74hx
Agent used a JSON-based clone for constructor options, which silently removed function-valued TLS options such as checkServerIdentity. Applications relying on custom certificate or public-key verification could therefore accept a certificate that the callback was intended to reject. This release preserves TLS options when creating per-origin dispatchers.
Cache poisoning and cross-user disclosure through cross-origin redirects
CVE-2026-109829 · GHSA-4w7w-5xrc-9h26
When an originless Agent combined redirect and shared-cache interceptors as compose(redirect(), cache()), a response from a cross-origin redirect could be stored under the original URL. This could allow persistent cache poisoning or disclosure of user-specific responses to later callers. This release verifies the response origin before caching and preserves redirect-hop cache-control policy.
Denial of service through excessive Content-Encoding values
CVE-2026-109869 · GHSA-xjj6-f33q-929c
A malicious HTTP server could crash the Node.js process by returning more than five content codings and closing the connection before sending the body. Although fetch() rejected the response, an error from an orphaned internal stream could remain unhandled. This release validates the content-encoding chain before creating the body stream and aborts oversized chains safely.
Medium severity
Denial of service through the decompress interceptor
CVE-2026-87029 · GHSA-55wc-3pg8-jfw6
An exception thrown by a downstream response handler from an asynchronous decompression callback could escape as an uncaught exception. A server could trigger this when decompress was composed with a handler such as dump with a size limit. This release converts downstream handler exceptions into per-request errors.
Subresource Integrity bypass with non-lowercase algorithm tokens
CVE-2026-109841 · GHSA-f72v-6w45-q472
fetch() treated valid mixed-case or uppercase SRI algorithm tokens, such as SHA256, as unknown and could accept a response whose body did not match the configured digest. This release normalizes algorithm tokens before validation and digest selection.
Denial of service through unbounded EventSource parser state
CVE-2026-109924 · GHSA-4qv8-2p9j-2685
A malicious Server-Sent Events endpoint could exhaust process memory by sending many tiny data: fields without completing an event, or by splitting an unfinished line across many chunks. This release bounds retained EventSource parser state, including field counts, buffered chunks, unfinished-line length, and retained field data.
Denial of service through unbounded automatic WebSocket PONG buffering
CVE-2026-109932 · GHSA-9fm3-97px-rjf6
A malicious WebSocket server could exhaust process memory by flooding the client with PING frames while not reading the automatic PONG responses. undici previously ignored socket backpressure and allowed the outbound queue to grow without bound. This release pauses frame parsing when PONG writes encounter backpressure and resumes after the socket drains.
Full Changelog: v8.12.1...v8.12.2