CVE-2026-39821
Critical
Description
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".
SeverityCritical
CVSS9.6
Exploit probability—
Product
Golang Net
PublishedMay 22, 2026
First seenMay 22, 2026
Weakness typeCWE-1289CWE-1289
How to fix
Update
- golang net0.55.0 or later
- stdlib1.25.13, 1.26.6, 1.27.0-rc.3 or later
- golang.org/x/net0.55.0 or later
Vendor advisories
- access.redhat.com/errata/RHSA-2026:42079
- access.redhat.com/errata/RHSA-2026:42080
- access.redhat.com/errata/RHSA-2026:41019
- access.redhat.com/errata/RHSA-2026:66350
- access.redhat.com/errata/RHSA-2026:54191
- access.redhat.com/errata/RHSA-2026:42078
- access.redhat.com/errata/RHSA-2026:54757
- access.redhat.com/errata/RHSA-2026:54580
- access.redhat.com/errata/RHSA-2026:34789
- access.redhat.com/errata/RHSA-2026:42082
- access.redhat.com/errata/RHSA-2026:36796
- access.redhat.com/errata/RHSA-2026:57845
Affected products
| Product | Affected versions | Fixed in |
|---|---|---|
| golang net | v < 0.55.0 | 0.55.0 |
| stdlibGo | v < 1.25.13, 1.26.0-0 ≤ v < 1.26.6, 1.27.0-0 ≤ v < 1.27.0-rc.3 | 1.25.13, 1.26.6, 1.27.0-rc.3 |
| golang.org/x/netGo | v < 0.55.0 | 0.55.0 |
| microsoft azl3_application-gateway-kubernetes-ingress_1.7.7-3 | No range specified | — |
| microsoft azl3_azcopy_10.25.1-4 | No range specified | — |
| microsoft azl3_azurelinux-image-tools_1.2.0-2 | No range specified | — |
| microsoft azl3_cert-manager_1.12.15-6 | No range specified | — |
| microsoft azl3_cf-cli_8.7.11-5 | No range specified | — |
| microsoft azl3_cloud-provider-kubevirt_0.5.1-3 | No range specified | — |
| microsoft azl3_containerd2_2.1.6-2 | No range specified | — |
| microsoft azl3_containerized-data-importer_1.62.0-3 | No range specified | — |
| microsoft azl3_coredns_1.11.4-15 | No range specified | — |
| microsoft azl3_cri-tools_1.32.0-4 | No range specified | — |
| microsoft azl3_docker-buildx_0.14.0-11 | No range specified | — |
| microsoft azl3_docker-cli_25.0.7-2 | No range specified | — |
| microsoft azl3_docker-compose_2.27.0-9 | No range specified | — |
| microsoft azl3_etcd_3.5.28-1 | No range specified | — |
| microsoft azl3_flannel_0.24.2-26 | No range specified | — |
| microsoft azl3_gh_2.62.0-15 | No range specified | — |
| microsoft azl3_git-lfs_3.6.1-2 | No range specified | — |
| microsoft azl3_golang_1.25.9-1 | No range specified | — |
| microsoft azl3_golang_1.26.2-1 | No range specified | — |
| microsoft azl3_ignition-flatcar_2.22.0-2 | No range specified | — |
| microsoft azl3_influxdb_2.7.5-15 | No range specified | — |
| microsoft azl3_jx_3.10.182-3 | No range specified | — |
| microsoft azl3_kata-containers_3.19.1.kata3-1 | No range specified | — |
| microsoft azl3_kata-containers-cc_3.15.0.aks0-9 | No range specified | — |
| microsoft azl3_keda_2.14.1-11 | No range specified | — |
| microsoft azl3_kube-vip-cloud-provider_0.0.10-5 | No range specified | — |
| microsoft azl3_kubernetes_1.30.10-23 | No range specified | — |
| microsoft azl3_kubevirt_1.7.1-2 | No range specified | — |
| microsoft azl3_kured_1.15.0-3 | No range specified | — |
| microsoft azl3_moby-containerd-cc_1.7.7-11 | No range specified | — |
| microsoft azl3_moby-engine_25.0.3-17 | No range specified | — |
| microsoft azl3_multus_4.0.2-7 | No range specified | — |
| microsoft azl3_opa_0.63.0-3 | No range specified | — |
| microsoft azl3_packer_1.9.5-13 | No range specified | — |
| microsoft azl3_prometheus-adapter_0.12.0-5 | No range specified | — |
| microsoft azl3_prometheus-node-exporter_1.7.0-3 | No range specified | — |
| microsoft azl3_prometheus-process-exporter_0.8.2-3 | No range specified | — |
| microsoft azl3_skopeo_1.14.4-10 | No range specified | — |
| microsoft azl3_sriov-network-device-plugin_3.7.0-5 | No range specified | — |
| microsoft azl3_telegraf_1.31.0-19 | No range specified | — |
| microsoft azl3_vitess_19.0.4-9 | No range specified | — |
| microsoft azl3_etcd_3.5.30-2 | No range specified | — |
| microsoft azl3_kata-containers_3.19.1.kata3-4 | No range specified | — |
| microsoft azl3_kata-containers-cc_3.15.0.aks0-12 | No range specified | — |
| microsoft azl3_moby-engine_25.0.3-18 | No range specified | — |
| microsoft azl3_moby-containerd-cc_1.7.7-13 | No range specified | — |
| microsoft azl3_git-lfs_3.6.1-4 | No range specified | — |
| microsoft azl3_golang_1.25.10-1 | No range specified | — |
| microsoft azl3_golang_1.26.3-1 | No range specified | — |
| microsoft azl3_kubernetes_1.30.10-25 | No range specified | — |
| microsoft azl3_sriov-network-device-plugin_3.7.0-6 | No range specified | — |
| microsoft azl3_vitess_19.0.4-10 | No range specified | — |
| microsoft azl3_golang_1.27.0-1 | No range specified | — |
| microsoft azl3_kubevirt-openvmm_1.9.0-1 | No range specified | — |
Check your version
Choose the product and enter the version you run to see whether it falls in the affected range.
In the Intelligence 360 plan
Attack Surface Management
See the assets tied to your domains, the technologies they run and known vulnerabilities in one list.