golang.org/x/net/idna pre-0.55.0 IDN bug allows silent ASCII/Unicode mix
CVE-2026-39821 Published on May 22, 2026

Invoking failure to reject ASCII-only Punycode-encoded labels in golang.org/x/net/idna
The ToASCII and ToUnicode functions incorrectly accept Punycode-encoded labels that decode to an ASCII-only label. For example, ToUnicode("xn--example-.com") incorrectly returns the name "example.com" rather than an error. This behavior can lead to privilege escalation in programs using the idna package. For example, a program which performs privilege checks on the ASCII hostname may reject "example.com" but permit "xn--example-.com". If that program subsequently converts the ASCII hostname to Unicode, it will inadvertently permits access to the Unicode name "example.com".

NVD

Vulnerability Analysis

CVE-2026-39821 can be exploited with network access, and requires small amount of user privileges. This vulnerability is consided to have a high level of attack complexity. The potential impact of an exploit of this vulnerability is considered to have a high impact on confidentiality and integrity, and no impact on availability.

Attack Vector:
NETWORK
Attack Complexity:
HIGH
Privileges Required:
LOW
User Interaction:
NONE
Scope:
CHANGED
Confidentiality Impact:
HIGH
Integrity Impact:
HIGH
Availability Impact:
NONE

Weakness Type

Improper Validation of Unsafe Equivalence in Input

The product receives an input value that is used as a resource identifier or other type of reference, but it does not validate or incorrectly validates that the input is equivalent to a potentially-unsafe value.


Products Associated with CVE-2026-39821

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Affected Versions

golang.org/x/net/idna: Red Hat Enterprise Linux 10: Red Hat Enterprise Linux 10: Red Hat Enterprise Linux 10: Red Hat Enterprise Linux 10: Red Hat Enterprise Linux 10: Red Hat Enterprise Linux 10: Red Hat Enterprise Linux 10: Red Hat Enterprise Linux 8: Red Hat Enterprise Linux 8: Red Hat Enterprise Linux 8: Red Hat Enterprise Linux 8: Red Hat Enterprise Linux 9: Red Hat Enterprise Linux 9: Red Hat Enterprise Linux 9: Red Hat Enterprise Linux 9: Red Hat Enterprise Linux 9: Red Hat Enterprise Linux 9: Red Hat OpenShift Container Platform 4.22: Red Hat RHEM 1.0 for RHEL 9: Red Hat RHEM 1.1 for RHEL 10: Red Hat RHEM 1.1 for RHEL 9: Red Hat Cluster Observability Operator 1.5.0: Red Hat Cluster Observability Operator 1.5.0: Red Hat Cluster Observability Operator 1.5.0: Red Hat Cluster Observability Operator 1.5.0: Red Hat Cluster Observability Operator 1.5.0: Red Hat Cluster Observability Operator 1.5.0: Red Hat Cluster Observability Operator 1.5.0: Red Hat Cluster Observability Operator 1.5.0: Red Hat Cluster Observability Operator 1.5.0: Red Hat DevWorkspace Operator 0.42: Logging Subsystem for Red Hat OpenShift 6.4: Red Hat multicluster engine for Kubernetes 2.6: Red Hat multicluster engine for Kubernetes 2.6: Red Hat multicluster engine for Kubernetes 2.6: Red Hat multicluster engine for Kubernetes 2.8: Red Hat multicluster engine for Kubernetes 2.8: Red Hat multicluster engine for Kubernetes 2.9: Red Hat Multicluster Global Hub 1.4.5: Red Hat Advanced Cluster Management for Kubernetes 2.13: Red Hat Advanced Cluster Management for Kubernetes 2.13: Red Hat Advanced Cluster Management for Kubernetes 2.13: Red Hat Advanced Cluster Management for Kubernetes 2.13: Red Hat Advanced Cluster Management for Kubernetes 2.13: Red Hat Advanced Cluster Management for Kubernetes 2.13: Red Hat Advanced Cluster Management for Kubernetes 2.13: Red Hat Advanced Cluster Management for Kubernetes 2.13: Red Hat Advanced Cluster Management for Kubernetes 2.13: Red Hat Advanced Cluster Management for Kubernetes 2.13: Red Hat Advanced Cluster Management for Kubernetes 2.13: Red Hat Advanced Cluster Management for Kubernetes 2.13: Red Hat Advanced Cluster Management for Kubernetes 2.13: Red Hat Advanced Cluster Management for Kubernetes 2.13: Red Hat Advanced Cluster Management for Kubernetes 2.13: Red Hat Advanced Cluster Management for Kubernetes 2.13: Red Hat Advanced Cluster Management for Kubernetes 2.13: Red Hat Advanced Cluster Management for Kubernetes 2.13: Red Hat Advanced Cluster Management for Kubernetes 2.13: Red Hat Advanced Cluster Security for Kubernetes 4.10: Red Hat Advanced Cluster Security for Kubernetes 4.11: Red Hat Advanced Cluster Security for Kubernetes 4.9: Red Hat Edge Manager 1.0: Red Hat Edge Manager 1.1: Red Hat Edge Manager 1.1: Red Hat Enterprise Linux AI 3.4: Red Hat Enterprise Linux AI 3.4: Red Hat Enterprise Linux AI 3.4: Red Hat Enterprise Linux AI 3.4: Red Hat Enterprise Linux AI 3.4: Red Hat Enterprise Linux AI 3.4: Red Hat Enterprise Linux AI 3.4: Red Hat Hardened Images: Red Hat Hardened Images: Red Hat OpenShift Builds 1.7.4: Red Hat OpenShift Builds 1.7.4: Red Hat OpenShift Builds 1.8.1: Red Hat OpenShift Builds 1.8.1: Red Hat Openshift Data Foundation 4.22: Red Hat Openshift Data Foundation 4.22: Red Hat Openshift Data Foundation 4.22: Red Hat Openshift Data Foundation 4.22: Red Hat Openshift Data Foundation 4.22: Red Hat Openshift Data Foundation 4.22: Red Hat Openshift Data Foundation 4.22: Red Hat Openshift Data Foundation 4.22: Red Hat Openshift Data Foundation 4.22: Red Hat Openshift Data Foundation 4.22: Red Hat Openshift Data Foundation 4.22: Red Hat Openshift Data Foundation 4.22: Red Hat Openshift Data Foundation 4.22: Red Hat Openshift Data Foundation 4.22: Red Hat Openshift Data Foundation 4.22: Red Hat Openshift Data Foundation 4.22: Red Hat Openshift Data Foundation 4.22: Red Hat Openshift Data Foundation 4.22: Red Hat Openshift Data Foundation 4.22: Red Hat Openshift Data Foundation 4.22: Red Hat Openshift Data Foundation 4.22: Red Hat Openshift Data Foundation 4.22: Red Hat Openshift Data Foundation 4.22: Red Hat Openshift Data Foundation 4.22: Red Hat Openshift Data Foundation 4.22: Red Hat Openshift Data Foundation 4.22: Red Hat Openshift Data Foundation 4.22: Red Hat OpenShift Dev Spaces 3.29: Red Hat OpenShift GitOps 1.19: Red Hat OpenShift GitOps 1.20: Red Hat OpenShift Service Mesh 2.6: Red Hat OpenShift Service Mesh 3: Red Hat OpenShift Service Mesh 3.1: Red Hat OpenShift Service Mesh 3.2: Red Hat OpenShift Service Mesh 3.3: Red Hat Quay 3.10: Red Hat Quay 3.16: Red Hat Quay 3.9: Red Hat Trusted Artifact Signer 1.4: Assisted Installer for Red Hat OpenShift Container Platform 2: cert-manager Operator for Red Hat OpenShift: Red Hat Compliance Operator: Red Hat Confidential Compute Attestation: Red Hat Confidential Compute Attestation: Red Hat Cryostat 4: Red Hat Deployment Validation Operator: External Secrets Operator for Red Hat OpenShift: Red Hat Fence Agents Remediation Operator: Red Hat File Integrity Operator: Red Hat Gatekeeper 3: Red Hat Logical Volume Manager Storage: Red Hat Logical Volume Manager Storage: Red Hat Logical Volume Manager Storage: Red Hat Machine Deletion Remediation Operator: Red Hat Migration Toolkit for Applications 8: Red Hat Migration Toolkit for Containers: Red Hat Multiarch Tuning Operator: Red Hat Multicluster Engine for Kubernetes: Red Hat Multicluster Engine for Kubernetes: Red Hat Multicluster Engine for Kubernetes: Red Hat Multicluster Engine for Kubernetes: Red Hat Multicluster Engine for Kubernetes: Red Hat Multicluster Engine for Kubernetes: Red Hat Multicluster Engine for Kubernetes: Red Hat Multicluster Engine for Kubernetes: Red Hat Multicluster Engine for Kubernetes: Red Hat Multicluster Engine for Kubernetes: Red Hat Multicluster Engine for Kubernetes: Red Hat Multicluster Engine for Kubernetes: Red Hat Multicluster Engine for Kubernetes: Red Hat Multicluster Engine for Kubernetes: Red Hat 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Enterprise Linux AI (RHEL AI) 3: Red Hat Lightspeed for Runtimes Operator: Red Hat OpenShift AI (RHOAI): Red Hat OpenShift AI (RHOAI): Red Hat OpenShift AI (RHOAI): Red Hat OpenShift AI (RHOAI): Red Hat OpenShift AI (RHOAI): Red Hat OpenShift AI (RHOAI): Red Hat OpenShift AI (RHOAI): Red Hat OpenShift AI (RHOAI): Red Hat OpenShift AI (RHOAI): Red Hat OpenShift AI (RHOAI): Red Hat OpenShift AI (RHOAI): Red Hat OpenShift AI (RHOAI): Red Hat OpenShift AI (RHOAI): Red Hat OpenShift AI (RHOAI): Red Hat OpenShift AI (RHOAI): Red Hat OpenShift AI (RHOAI): Red Hat OpenShift AI (RHOAI): Red Hat OpenShift AI (RHOAI): Red Hat OpenShift AI (RHOAI): Red Hat OpenShift AI (RHOAI): Red Hat OpenShift AI (RHOAI): Red Hat OpenShift AI (RHOAI): Red Hat OpenShift AI (RHOAI): Red Hat OpenShift AI (RHOAI): Red Hat OpenShift AI (RHOAI): Red Hat OpenShift AI (RHOAI): Red Hat OpenShift AI (RHOAI): Red Hat OpenShift AI (RHOAI): Red Hat OpenShift AI (RHOAI): Red Hat OpenShift AI (RHOAI): Red Hat OpenShift AI 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6: Red Hat Service Interconnect 1: Red Hat Service Interconnect 2: Red Hat Web Terminal: Red Hat Security Profiles Operator: Red Hat streams for Apache Kafka 3: Red Hat Zero Trust Workload Identity Manager: Red Hat Zero Trust Workload Identity Manager - Tech Preview:

Exploit Probability

EPSS
0.36%
Percentile
27.58%

EPSS (Exploit Prediction Scoring System) scores estimate the probability that a vulnerability will be exploited in the wild within the next 30 days. The percentile shows you how this score compares to all other vulnerabilities.