Update to go1.26.9

[vvoland]

Summary

• https://github.com/golang/go/issues?q=milestone%3AGo1.26.9+label%3ACherryPickApproved
• full diff: golang/go@go1.26.8...go1.26.9

This release includes 15 security fixes following the security policy:

• net/http: HTTP/2 server crash due to HPACK encoder race

  HTTP/2 servers could end up crashing due to inadvertently
  modifying its HPACK encoder concurrently. This happens because the
  server modifies the HPACK encoder from two goroutines without
  synchronization: one uses the encoder to encode a HEADERS frame as part
  of a response sent to a client and the other modifies the encoder's
  table size when handling a SETTINGS frame containing
  SETTINGS_HEADER_TABLE_SIZE that a client sends. A malicious client can
  repeatedly send a request while changing the header table size to crash
  the server.

  Fix this issue by not applying SETTINGS_HEADER_TABLE_SIZE immediately.
  Instead, buffer any SETTINGS_HEADER_TABLE_SIZE received, and only apply
  the new value prior to the next time the server writes a frame.

  Thanks to RyotaK (https://ryotak.net) of GMO Flatt Security Inc. for reporting this issue.

  This is CVE-2026-97032 and Go issue https://go.dev/issue/81867.

• net/http: HTTP/2 server memory exhaustion due to Trailer headers

  When "Trailer" headers are sent by a client, the HTTP server internally
  uses the header values to populate the Request.Trailer map passed to the
  server handler. Because Request.Trailer is a map, each entry incurs
  memory overhead. For HTTP/2 servers, a malicious client can exploit this
  by sending a "Trailer" header that declares a large number of fields,
  causing the server to allocate a disproportionate amount of memory while
  bypassing Server.MaxHeaderValueCount and Server.MaxHeaderBytes limits.
  This exploit is not applicable for HTTP/1 servers, which do not support
  multiplexing a large number of requests over one TCP connection, and
  whose Server.MaxHeaderBytes are calculated differently.

  Server.MaxHeaderValueCount and Server.MaxHeaderBytes limits are now
  applied towards the trailer fields declared in "Trailer" headers.

  Thanks to RyotaK (https://ryotak.net) of GMO Flatt Security Inc. for reporting this issue.

  This is CVE-2026-78659 and Go issue https://go.dev/issue/81857.

• crypto/tls: reject malformed ECH outer extension references

  Multiple ECH outer extension references are not
  permitted under RFC 9849; previously, a client
  could send a well-crafted packet that could
  trigger memory exhaustion in the server process
  by specifying multiple references.

  We now reject these as malformed and curb the
  memory amplification vector as a result.

  This is CVE-2026-97031 and Go issue https://go.dev/issue/81855.

• cmd/go: checksum bypass for golang.org/fips140

  Previously, a user operating inside of a malicious
  Go project that defines a bogus golang.org/fips140
  and operates a malicious GOMODPROXY the user chooses
  to connect to can serve an arbitrary module in its
  place.

  We now unpack the trusted ziphash for the bundled
  golang.org/fips140 module and construct its entry
  in the GOMODCACHE such that it can be verified by
  the toolchain.

  This is CVE-2026-94444 and Go issue https://go.dev/issue/81833.

• cmd/go: checksum database bypass for golang.org/toolchain

  Previously, a user operating inside of a malicious
  Go project that defines a bogus golang.org/toolchain
  go.sum entry and operates a malicious GOMODPROXY the
  user chooses to use can bypass the intended checksum.

  We now ensure that golang.org/toolchain always goes
  to the network for the canonical checksum.

  This is CVE-2026-94447 and Go issue https://go.dev/issue/81834.

• html/template: reset context tracking on consecutive template expressions

  When a JavaScript template literal contains
  consecutive expressions, the context tracking
  state was not properly reset upon entering a
  new expression.

  We now ensure that template-literal expression
  entries correctly reset context variables so all
  subsequent regular expression literals are
  accurately recognized and escaped.

  This is CVE-2026-94448 and Go issue https://go.dev/issue/81821.

• html/template: recognize yield as regexp preceder keyword

  A trusted template author may have previously
  written a valid template wherein the use of
  the yield keyword would not be correctly
  escaped.

  We now ensure that valid keyword uses are
  escaped and non-keyword uses are not escaped.

  This is CVE-2026-97030 and Go issue https://go.dev/issue/81823.

• net/textproto, mime/multipart: memory limit bypass when parsing MIME headers

  Parsing a multipart form could bypass memory limits and read an
  arbitrarily long line into memory when the remaining limit at the
  start of a part was less than 400 bytes.

  Multipart form memory limits are now properly enforced in this situation.

  Thanks to Jakub Ciolek (https://ciolek.dev) for reporting this issue.

  This is CVE-2026-94440 and Go issue https://go.dev/issue/81741.

• net/http: HTTP/1 client connection desynchronization after CONNECT rejection

  When http.Transport sends an HTTP/1 CONNECT request with a non-empty
  Request.Body, it writes the body directly to the connection without
  framing after the request headers. If the server rejects the CONNECT
  request with a non-2xx keep-alive response, Transport returns the
  connection to the idle pool. Because CONNECT requests do not have a
  request body, the server may interpret the trailing body bytes as a
  subsequent pipelined HTTP/1.1 request on the connection, leaving the
  pooled connection desynchronized and causing the next caller that reuses
  it to read the response to the injected request. In reverse proxies
  (including httputil.ReverseProxy) that forward CONNECT requests through
  a shared Transport, this can lead to cross-user response poisoning.

  The HTTP/1 transport now closes a connection after sending a CONNECT
  request, regardless of the response status.

  In addition, ReverseProxy now rejects incoming CONNECT requests
  with a 405 Method Not Allowed response. ReverseProxy has never handled
  CONNECT requests in a useful fashion (it does not convert the
  connection into a bidirectional tunnel), so we do not expect this
  change to negatively affect any current users.

  Thanks to Xclow3n (Rajat Raghav) for reporting this issue.

  This is CVE-2026-56866 and Go issue https://go.dev/issue/81740.

• net/http: HTTP/1 server connection desynchronization after 2xx CONNECT response

  When an HTTP server handler sent a 2xx response to an HTTP/1 CONNECT request
  and returned without hijacking the connection, the server improperly continued
  to read and serve requests from the connection. Since a 2xx response to an
  HTTP/1 CONNECT converts the connection into a tunnel, the server should not
  treat the connection as continuing to contain HTTP.

  The impact of this misbehavior is mostly limited to potential request smuggling,
  where an intermediate proxy considers the data on the connection to be tunneled
  and the server considers it to be HTTP.

  The HTTP/1 server now always closes a connection after responding to a CONNECT
  request, regardless of the response status.

  Thanks to Jakub Ciolek (https://ciolek.dev) for reporting this issue.

  This is CVE-2026-94439 and Go issue https://go.dev/issue/81744.

• net/http: excessive CPU consumption from repeated initial window changes

  A malicious HTTP/2 peer could cause excessive CPU consumption in the
  client or server by opening a large number of streams and then sending
  many small SETTINGS frames containing SETTINGS_INITIAL_WINDOW_SIZE values.

  The HTTP/2 client and server now efficiently handle changes to the
  initial window size (O(1) rather than O(number of streams)).

  Thanks to Jakub Ciolek (https://ciolek.dev) for reporting this issue.

  This is CVE-2026-78669 and Go issue https://go.dev/issue/81742.

• net/http: HTTP/2 transport accepts malformed framing-related headers

  Historically, we have been rather lax about malformed framing-related
  headers in our HTTP/2 implementation, as they cannot interfere with
  HTTP/2 framing. However, this makes it possible for our HTTP/2
  implementation to forward responses containing such headers to an HTTP/1
  client when acting as a reverse proxy. If the HTTP/1 client also does
  not behave strictly enough, this can result in response smuggling.

  We now delete malformed framing-related headers when received by our
  HTTP/2 transport, so they will not be forwarded to a potentially
  vulnerable HTTP/1 client.

  Thanks to TJ Barton for reporting this issue.

  This is CVE-2026-78660 and Go issue https://go.dev/issue/81115.

• os: Root.Mkdir(All) can follow junctions out of the root on Windows

  On Windows, when the target of Root.Mkdir or Root.MkdirAll was a junction
  pointing to an empty location, the operation would create a directory at
  the junction target even when that target was located outside the root.
  This only applies to operations where the last path component is a
  junction (path/to/junction, but not path/junction/target).

  Root.Mkdir and Root.MkdirAll now correctly avoid resolving junctions.

  Thanks to Daniele Ballarini for reporting this issue.

  This is CVE-2026-56857 and Go issue https://go.dev/issue/81739.

• net/http: lack of limit on size of parsed Range headers

  When parsing a Range header containing a large number of small ranges,
  FileServer(FS), ServeContent, and ServeFile(FS) could consume an excessive
  amount of CPU.

  These functions now ignore Range headers containing more than 200 ranges.

  The limit is controlled by the new httpservecontentmaxranges=
  GODEBUG setting. Setting GODEBUG=httpservecontentmaxranges=0
  disables the limit.

  Thanks to Jakub Ciolek (https://ciolek.dev) for reporting this issue.

  This is CVE-2026-78667 and Go issue https://go.dev/issue/81858.

• net/http: double flow control refund on HTTP/2 server streams

  The HTTP/2 server could refund connection-level flow control twice for the same data:
  Once when a client resets a stream (refunding data for any sent-but-unread portion
  of the stream), and again when a request handler reads the buffered data.
  A malicious client could exploit this to bypass the configured connection-level
  flow control limit (MaxReceiveBufferPerConnection). Total buffered data is still
  limited by the concurrent stream limit and stream-level flow control.

  The HTTP/2 server now waits to refund connection-level flow control for reset
  streams until after the request handler is complete.

  Thanks to Ali Sherif (https://www.linkedin.com/in/ali-sherif-13812b276/) for reporting this issue.

  This is CVE-2026-78663 and Go issue https://go.dev/issue/81743.

release notes: https://go.dev/doc/devel/release#go1.26.9

Release notes (optional)

Update Go runtime to [1.26.9](https://go.dev/doc/devel/release#go1.26.9)

[docker-agent]

Assessment: 🟢 APPROVE

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!

[thaJeztah]

LGTM

[docker-agent]

Assessment: 🟢 APPROVE

This incremental review covers commits since 9db98021278c.

The changes in this incremental diff are a Go runtime update (Go 1.26.9) with vendored golang.org/x/net HTTP/2 library security patches. The updated files include CI workflow version bumps, Dockerfile version updates, and vendor/golang.org/x/net/http2 + vendor/golang.org/x/net/internal/httpcommon changes.

The code changes are well-structured upstream security fixes addressing 15 CVEs in Go 1.26.9. The key changes reviewed:

• Flow control refactor (flow.go): The new connOutflow/outflow model correctly computes per-stream windows as conn.initial + delta, eliminating the need to iterate all streams on SETTINGS_INITIAL_WINDOW_SIZE updates.
• HPACK table size (server.go): Deferred application of SETTINGS_HEADER_TABLE_SIZE fixes the concurrent modification race (CVE-2026-97032).
• Trailer header budget (frame.go): Separate headersRemainSize/trailersRemainSize budgets correctly enforce limits for trailer declarations.
• Gzip reader pool (gzip.go): The mutex drop-and-reacquire pattern during gzipPoolGet is correctly guarded with the errConcurrentRead sentinel value.
• Dial coalescing (transport_wrap.go): The leader/follower pattern is consistent with the overall dial retry logic.

No CONFIRMED or LIKELY bugs were found in the introduced code.