-------- Forwarded Message --------
Subject: [security] Go 1.27.2 and Go 1.26.9 are released
Date: Thu, 8 Oct 2026 18:08:50 +0000
From: [email protected]
To: [email protected]
Hello gophers,
We have just released Go versions 1.27.2 and 1.26.9, minor point releases.
These releases include 15 security fixes following the security policy
<https://go.dev/doc/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 <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
<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 <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
<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
<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
<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
<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
<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
<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 <https://ciolek.dev>) for
reporting this issue.
This is CVE-2026-94440 and Go issue https://go.dev/issue/81741
<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
<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 <https://ciolek.dev>) for
reporting this issue.
This is CVE-2026-94439 and Go issue https://go.dev/issue/81744
<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 <https://ciolek.dev>) for
reporting this issue.
This is CVE-2026-78669 and Go issue https://go.dev/issue/81742
<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
<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
<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 <https://ciolek.dev>) for
reporting this issue.
This is CVE-2026-78667 and Go issue https://go.dev/issue/81858
<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/
<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
<https://go.dev/issue/81743>.
View the release notes for more information:
https://go.dev/doc/devel/release#go1.27.2
You can download binary and source distributions from the Go website:
https://go.dev/dl/
To compile from source using a Git clone, update to the release with
|git checkout go1.27.2| and build as usual.
Thanks to everyone who contributed to the releases.
Cheers,
Dmitri and Michael for the Go team
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