CVE-2026-39821
Description
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.
Statement
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.
Mitigation
Upgrade to a fixed golang.org/x/net release that includes the idna correction, via updated golang or dependent package rebuilds.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 8.2 | N/A | 8.2 |
| Attack Vector | Network | N/A | Network |
| Attack Complexity | High | N/A | High |
| Privileges Required | Low | N/A | Low |
| User Interaction | None | N/A | None |
| Scope | Changed | N/A | Changed |
| Confidentiality | High | N/A | High |
| Integrity Impact | High | N/A | High |
| Availability Impact | None | N/A | None |
Vector
Red Hat: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:N
cve.org: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:N
Understanding the Weakness (CWE)
Other
Technical Impact: Varies by Context
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