CVE-2026-39821

A flaw was found in golang.org/x/net/idna. ToASCII and ToUnicode incorrectly accept Punycode-encoded labels that decode to an ASCII-only hostname (for example, xn--example-.com returns example.com instead of an error). Applications that validate the ASCII form then convert to Unicode may grant access to a restricted hostname the ASCII check would have rejected.

golang.org/x/net/idna is vulnerable to privilege escalation through incorrect Punycode label handling in ToASCII and ToUnicode. An attacker who can supply a Punycode hostname that passes an ASCII-only authorization check may have it normalized to a restricted ASCII name the application intended to block. Red Hat exposure is broad across products shipping the Go toolchain or bundling golang.org/x/net, including RHEL and RHEL-AI golang RPMs, hummingbird Go runtimes, OpenShift and ODF container builds, and Ceph/OpenShift components compiled against affected x/net versions.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.

Upgrade to a fixed golang.org/x/net release that includes the idna correction, via updated golang or dependent package rebuilds.