ALAS2-2026-4005

References: CVE-2026-56866  CVE-2026-78659  CVE-2026-78660  CVE-2026-78663  CVE-2026-78667  CVE-2026-78669  CVE-2026-94439  CVE-2026-94440  CVE-2026-94444  CVE-2026-94447  CVE-2026-94448  CVE-2026-97030  CVE-2026-97031  CVE-2026-97032 
FAQs regarding Amazon Linux ALAS/CVE Severity

Issue Overview:

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.

NOTE: https://www.openwall.com/lists/oss-security/2026/10/08/9
NOTE: https://github.com/golang/go/issues/81740
NOTE: Fixed by: https://github.com/golang/go/commit/76875df0f3425f69e4dc2c439040a248b6107854 (go1.27.2)
NOTE: Fixed by: https://github.com/golang/go/commit/3fe1aac0ce941cb16b0ec5d489827cf1c58197c4 (go1.26.9) (CVE-2026-56866)

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.

NOTE: https://www.openwall.com/lists/oss-security/2026/10/08/9
NOTE: https://github.com/golang/go/issues/81857
NOTE: Fixed by: https://github.com/golang/go/commit/cbb0fb8b51cba866018b8a0fb4b5458f16c5c80b (go1.27.2)
NOTE: Fixed by: https://github.com/golang/go/commit/6e049521882c944afc1e519a83971ec421dc2974 (go1.26.9) (CVE-2026-78659)

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.

NOTE: https://www.openwall.com/lists/oss-security/2026/10/08/9
NOTE: https://github.com/golang/go/issues/81115
NOTE: Fixed by: https://github.com/golang/go/commit/072779d81582543bf2872c259e0c6cceea728de4 (go1.27.2)
TODO: check might need tracking for golang-golang-x-net (CVE-2026-78660)

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.

NOTE: https://www.openwall.com/lists/oss-security/2026/10/08/9
NOTE: https://github.com/golang/go/issues/81743
NOTE: Fixed by: https://github.com/golang/go/commit/31dc9e2449e394439498142451627af52626d7c4 (go1.27.2)
NOTE: Fixed by: https://github.com/golang/go/commit/6e049521882c944afc1e519a83971ec421dc2974 (go1.26.9) (CVE-2026-78663)

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.

NOTE: https://www.openwall.com/lists/oss-security/2026/10/08/9
NOTE: https://github.com/golang/go/issues/81858
NOTE: Fixed by: https://github.com/golang/go/commit/ababc3cd873d8acce1777268aa7a817e6b672028 (go1.27.2)
NOTE: Fixed by: https://github.com/golang/go/commit/eb25b4e532c5a01f99ef860ec66743a8783f992b (go1.26.9) (CVE-2026-78667)

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)).

NOTE: https://www.openwall.com/lists/oss-security/2026/10/08/9
NOTE: https://github.com/golang/go/issues/81742
NOTE: Fixed by: https://github.com/golang/go/commit/1d58cdaa1069e259b60c324ec77472f09f23d92e (go1.27.2)
NOTE: Fixed by: https://github.com/golang/go/commit/6e049521882c944afc1e519a83971ec421dc2974 (go1.26.9) (CVE-2026-78669)

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.

NOTE: https://www.openwall.com/lists/oss-security/2026/10/08/9
NOTE: https://github.com/golang/go/issues/81744
NOTE: Fixed by: https://github.com/golang/go/commit/e92229e24a387cc006a750af176b07a459ba71a1 (go1.27.2)
NOTE: Fixed by: https://github.com/golang/go/commit/087de1ff08ea620ac2f6ae26c939454cb793883a (go1.26.9) (CVE-2026-94439)

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.

NOTE: https://www.openwall.com/lists/oss-security/2026/10/08/9
NOTE: https://github.com/golang/go/issues/81741
NOTE: Fixed by: https://github.com/golang/go/commit/7c79b50a74b6d1aa4269b1827dda7d81f3717f9d (go1.27.2)
NOTE: Fixed by: https://github.com/golang/go/commit/d7a7aa8e6781ddf8dce12adf60a813d957d4763e (go1.26.9) (CVE-2026-94440)

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. (CVE-2026-94444)

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.

NOTE: https://www.openwall.com/lists/oss-security/2026/10/08/9
NOTE: https://github.com/golang/go/issues/81834
NOTE: Fixed by: https://github.com/golang/go/commit/68fa7699a27d745f90bf8630202e1a415d1b0769 (go1.27.2)
NOTE: Fixed by: https://github.com/golang/go/commit/7325b729f07c7ff255b9b5e3f427234ebd21ac47 (go1.26.9) (CVE-2026-94447)

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.

NOTE: https://www.openwall.com/lists/oss-security/2026/10/08/9
NOTE: https://github.com/golang/go/issues/81821
NOTE: Fixed by: https://github.com/golang/go/commit/b26d150e6985f804826f4fcb1aa33aa81e700b52 (go1.27.2)
NOTE: Fixed by: https://github.com/golang/go/commit/e59c03e695f2eaa26e308f756c83773afb034e47 (go1.26.9) (CVE-2026-94448)

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.

NOTE: https://www.openwall.com/lists/oss-security/2026/10/08/9
NOTE: https://github.com/golang/go/issues/81823
NOTE: Fixed by: https://github.com/golang/go/commit/6e2cfab0a1c1683c52f9e09270627b0c4e6446e3 (go1.27.2)
NOTE: Fixed by: https://github.com/golang/go/commit/5d84f6f08caf63b5f1300930368756bd34955f4a (go1.26.9) (CVE-2026-97030)

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.

NOTE: https://www.openwall.com/lists/oss-security/2026/10/08/9
NOTE: https://github.com/golang/go/issues/81855
NOTE: Fixed by: https://github.com/golang/go/commit/f022e61963529d5e691f0e42a87fd5b520f01636 (go1.27.2)
NOTE: Fixed by: https://github.com/golang/go/commit/eb1bf6e0c4f68b23409483b156e1455696508c6e (go1.26.9) (CVE-2026-97031)

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.

NOTE: https://www.openwall.com/lists/oss-security/2026/10/08/9
NOTE: https://github.com/golang/go/issues/81867
NOTE: Fixed by: https://github.com/golang/go/commit/12acaf3086437e140e2dd3b7d2c30fdd633c5fe0 (go1.27.2)
NOTE: Fixed by: https://github.com/golang/go/commit/6e049521882c944afc1e519a83971ec421dc2974 (go1.26.9) (CVE-2026-97032)

Issue Correction:
Run yum update golang or yum update --advisory ALAS2-2026-4005 to update your system.

New Packages:

aarch64:
    golang-1.26.9-1.amzn2.0.1.aarch64
    golang-bin-1.26.9-1.amzn2.0.1.aarch64
    golang-shared-1.26.9-1.amzn2.0.1.aarch64

noarch:
    golang-docs-1.26.9-1.amzn2.0.1.noarch
    golang-misc-1.26.9-1.amzn2.0.1.noarch
    golang-tests-1.26.9-1.amzn2.0.1.noarch
    golang-src-1.26.9-1.amzn2.0.1.noarch

src:
    golang-1.26.9-1.amzn2.0.1.src

x86_64:
    golang-1.26.9-1.amzn2.0.1.x86_64
    golang-bin-1.26.9-1.amzn2.0.1.x86_64
    golang-shared-1.26.9-1.amzn2.0.1.x86_64