ALAS2023-2026-3350

References: CVE-2026-111943  CVE-2026-78659  CVE-2026-78663 
FAQs regarding Amazon Linux ALAS/CVE Severity

Issue Overview:

Due to security concerns regarding a small set of intermediate certificates issued by a specific Certificate Authority (CA), the Go's crypto/x509 package is updated to not trust certificates issued by the affected intermediate certificates. This would prevent possible future misuse of certificate issued by the affected intermediate certificates.

Amazon Linux golang-based packages are being rebuilt with the fixed crypto/x509 package described in CVE-2026-111943 as a defense-in-depth measure against the eMudhra intermediate CA certificates with weak private keys.

By default, Go programs on Amazon Linux use the system-wide certificate authority (CA) store. Therefore, the primary fix for this issue is the ca-certificates update that removes the root CA certificates that signed the affected intermediates. Customers should ensure that update is installed: https://explore.alas.aws.amazon.com/CVE-2026-113470.html (CVE-2026-111943)

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)

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)

Issue Correction:
Run dnf update amazon-cloudwatch-agent --releasever 2023.12.20261102 or dnf update --advisory ALAS2023-2026-3350 --releasever 2023.12.20261102 to update your system.
More information on how to update your system can be found on this page: Amazon Linux 2023 documentation

New Packages:

aarch64:
    amazon-cloudwatch-agent-1.300073.2-1.amzn2023.aarch64

src:
    amazon-cloudwatch-agent-1.300073.2-1.amzn2023.src

x86_64:
    amazon-cloudwatch-agent-1.300073.2-1.amzn2023.x86_64