RHSA-2026:29980MediumCVSS 7.5

Red Hat Security Advisory: golang security, bug fix, and enhancement update

Published
June 25, 2026
Last Modified
October 31, 2026

🔗 CVE IDs covered (3)

CVE-2026-27145 →CVE-2026-42504 →CVE-2026-42507 →

📋 Description

CVE-2026-27145 — crypto/x509: golang: golang crypto/x509: Denial of Service via excessive processing of DNS SAN entries CVE-2026-42504 — mime: golang: Golang MIME: Denial of Service via maliciously-crafted MIME header CVE-2026-42507 — net/textproto: golang: Golang net/textproto: Misleading error messages via input injection

🎯 Affected products22

  • Red Hat Enterprise Linux AppStream (v. 10)
  • go-toolset-0:1.26.4-1.el10_2.aarch64 as a component of Red Hat Enterprise Linux AppStream (v. 10)
  • go-toolset-0:1.26.4-1.el10_2.ppc64le as a component of Red Hat Enterprise Linux AppStream (v. 10)
  • go-toolset-0:1.26.4-1.el10_2.s390x as a component of Red Hat Enterprise Linux AppStream (v. 10)
  • go-toolset-0:1.26.4-1.el10_2.x86_64 as a component of Red Hat Enterprise Linux AppStream (v. 10)
  • golang-0:1.26.4-1.el10_2.aarch64 as a component of Red Hat Enterprise Linux AppStream (v. 10)
  • golang-0:1.26.4-1.el10_2.ppc64le as a component of Red Hat Enterprise Linux AppStream (v. 10)
  • golang-0:1.26.4-1.el10_2.s390x as a component of Red Hat Enterprise Linux AppStream (v. 10)
  • golang-0:1.26.4-1.el10_2.src as a component of Red Hat Enterprise Linux AppStream (v. 10)
  • golang-0:1.26.4-1.el10_2.x86_64 as a component of Red Hat Enterprise Linux AppStream (v. 10)
  • golang-bin-0:1.26.4-1.el10_2.aarch64 as a component of Red Hat Enterprise Linux AppStream (v. 10)
  • golang-bin-0:1.26.4-1.el10_2.ppc64le as a component of Red Hat Enterprise Linux AppStream (v. 10)
  • golang-bin-0:1.26.4-1.el10_2.s390x as a component of Red Hat Enterprise Linux AppStream (v. 10)
  • golang-bin-0:1.26.4-1.el10_2.x86_64 as a component of Red Hat Enterprise Linux AppStream (v. 10)
  • golang-docs-0:1.26.4-1.el10_2.noarch as a component of Red Hat Enterprise Linux AppStream (v. 10)
  • golang-misc-0:1.26.4-1.el10_2.noarch as a component of Red Hat Enterprise Linux AppStream (v. 10)
  • golang-race-0:1.26.4-1.el10_2.aarch64 as a component of Red Hat Enterprise Linux AppStream (v. 10)
  • golang-race-0:1.26.4-1.el10_2.ppc64le as a component of Red Hat Enterprise Linux AppStream (v. 10)
  • golang-race-0:1.26.4-1.el10_2.s390x as a component of Red Hat Enterprise Linux AppStream (v. 10)
  • golang-race-0:1.26.4-1.el10_2.x86_64 as a component of Red Hat Enterprise Linux AppStream (v. 10)
  • golang-src-0:1.26.4-1.el10_2.noarch as a component of Red Hat Enterprise Linux AppStream (v. 10)
  • golang-tests-0:1.26.4-1.el10_2.noarch as a component of Red Hat Enterprise Linux AppStream (v. 10)

✅ Remediation

For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258 Workaround: A flaw was found in the Go standard library crypto/x509 package. When verifying a TLS certificate hostname, VerifyHostname processed each DNS Subject Alternative Name (SAN) entry in a loop and repeatedly split the candidate hostname on "." characters. For certificates with a very large DNS SAN list, CPU use could grow quadratically with the number of SAN entries and hostname labels. Because hostname verification runs before the certificate chain is built, this overhead can occur even when the certificate is not trusted. Red Hat rates this issue as Important. It affects Red Hat products that include the Go standard library crypto/x509 code from an affected Go toolchain version (before Go 1.25.11, or from Go 1.26.0 through Go 1.26.3). Applications and container images built with a fixed Go release (1.25.11 or later, or 1.26.4 or later) are not affected. Community distributions such as Fedora are also affected. Upstream fix: Go 1.25.11 and Go 1.26.4 (GO-2026-5037). Workaround: To mitigate this issue, restrict network access to services that process MIME headers from untrusted sources. Implement input validation and sanitization for all incoming data, especially MIME headers, to prevent maliciously crafted content from being processed by applications utilizing the vulnerable Golang MIME package. Workaround: Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base, or stability.

🔗 References (5)