CVE-2026-39821: Invoking failure to reject ASCII-only Punycode-encoded labels in golang.org/x/net/idna

Published May 22, 2026
·
Updated

Invoking failure to reject ASCII-only Punycode-encoded labels in golang.org/x/net/idna

Other sources

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".

— MITRE

Affected Software

101 affected componentsFixes available
go/golang.org/x/net/idna
Microsoft azl3 prometheus-process-exporter 0.8.2-3
Patch available
Microsoft azl3 multus 4.0.2-7
Patch available
Microsoft azl3 kata-containers 3.19.1.kata3-1
Patch available
Microsoft azl3 skopeo 1.14.4-10
Patch available
Microsoft azl3 telegraf 1.31.0-19
Patch available
Microsoft azl3 opa 0.63.0-3
Patch available
Microsoft azl3 jx 3.10.182-3
Patch available
Microsoft azl3 kata-containers-cc 3.15.0.aks0-9
Patch available
Microsoft azl3 keda 2.14.1-11
Patch available
Microsoft azl3 ignition-flatcar 2.22.0-2
Patch available
Microsoft azl3 gh 2.62.0-15
Patch available
Microsoft azl3 flannel 0.24.2-26
Patch available
Microsoft azl3 docker-buildx 0.14.0-11
Patch available
Microsoft azl3 docker-compose 2.27.0-9
Patch available
Microsoft azl3 containerd2 2.1.6-2
Patch available
Microsoft azl3 coredns 1.11.4-15
Patch available
Microsoft azl3 cloud-provider-kubevirt 0.5.1-3
Patch available
Microsoft azl3 azcopy 10.25.1-4
Patch available
Microsoft azl3 docker-cli 25.0.7-2
Patch available
Microsoft azl3 cf-cli 8.7.11-5
Patch available
Microsoft azl3 vitess 19.0.4-9
Patch available
Microsoft azl3 sriov-network-device-plugin 3.7.0-5
Patch available
Microsoft azl3 prometheus-node-exporter 1.7.0-3
Patch available
Microsoft azl3 kubevirt 1.7.1-2
Patch available
Microsoft azl3 influxdb 2.7.5-15
Patch available
Microsoft azl3 kube-vip-cloud-provider 0.0.10-5
Patch available
Microsoft azl3 etcd 3.5.28-1
Patch available
Microsoft azl3 cri-tools 1.32.0-4
Patch available
Microsoft azl3 containerized-data-importer 1.62.0-3
Patch available
Microsoft azl3 application-gateway-kubernetes-ingress 1.7.7-3
Patch available
Microsoft azl3 azurelinux-image-tools 1.2.0-2
Patch available
Microsoft azl3 cert-manager 1.12.15-6
Patch available
Microsoft azl3 prometheus-adapter 0.12.0-5
Patch available
Microsoft azl3 packer 1.9.5-13
Patch available
Microsoft azl3 kured 1.15.0-3
Patch available
Microsoft azl3 kubernetes 1.30.10-23
Patch available
Microsoft azl3 moby-containerd-cc 1.7.7-11
Patch available
Microsoft azl3 moby-engine 25.0.3-17
Patch available
Microsoft azl3 sriov-network-device-plugin 3.7.0-6
Patch available
Microsoft azl3 vitess 19.0.4-10
Patch available
Microsoft azl3 moby-engine 25.0.3-18
Patch available
Microsoft azl3 kubernetes 1.30.10-25
Patch available
Microsoft azl3 git-lfs 3.6.1-4
Patch available
Microsoft azl3 kata-containers 3.19.1.kata3-4
Patch available
Microsoft azl3 etcd 3.5.30-2
Patch available
Microsoft azl3 kata-containers-cc 3.15.0.aks0-12
Patch available
Microsoft azl3 git-lfs 3.6.1-2
Patch available
Golang Net Go<0.55.0
debian/golang-golang-x-net<=1:0.0+git20210119.5f4716e+dfsg-4, <=1:0.7.0+dfsg-1, <=1:0.27.0-2
1:0.55.0-1
Microsoft azl3 sriov-network-device-plugin 3.7.0-6<3.7.0-6
3.7.0-6
Microsoft azl3 vitess 19.0.4-10<19.0.4-10
19.0.4-10
Microsoft azl3 golang 1.25.10-1<1.25.11-2
1.25.11-2
Microsoft azl3 moby-engine 25.0.3-17<25.0.3-18
25.0.3-18
Microsoft azl3 kubernetes 1.30.10-25<1.30.10-25
1.30.10-25
Microsoft azl3 git-lfs 3.6.1-4<3.6.1-3
3.6.1-3
Microsoft azl3 moby-containerd-cc 1.7.7-11<1.7.7-13
1.7.7-13
Microsoft azl3 git-lfs 3.6.1-2<3.6.1-3
3.6.1-3
Microsoft azl3 golang 1.26.3-1<1.26.4-2
1.26.4-2
Microsoft azl3 kata-containers-cc 3.15.0.aks0-12<3.15.0.aks0-11
3.15.0.aks0-11
Microsoft azl3 kubernetes 1.30.10-23<1.30.10-25
1.30.10-25
Microsoft azl3 prometheus-adapter 0.12.0-5<0.12.0-6
0.12.0-6
Microsoft azl3 vitess 19.0.4-9<19.0.4-10
19.0.4-10
Microsoft azl3 moby-engine 25.0.3-18<25.0.3-18
25.0.3-18
Microsoft azl3 kata-containers 3.19.1.kata3-4<3.19.1.kata3-3
3.19.1.kata3-3
Microsoft azl3 prometheus-node-exporter 1.7.0-3<1.7.0-4
1.7.0-4
Microsoft azl3 sriov-network-device-plugin 3.7.0-5<3.7.0-6
3.7.0-6
Microsoft azl3 packer 1.9.5-13<1.9.5-14
1.9.5-14
Microsoft azl3 etcd 3.5.28-1<3.5.30-2
3.5.30-2
Microsoft azl3 etcd 3.5.30-2<3.5.30-2
3.5.30-2
Microsoft azl3 kured 1.15.0-3<1.15.0-5
1.15.0-5
Microsoft azl3 cri-tools 1.32.0-4<1.32.0-6
1.32.0-6
Microsoft azl3 containerized-data-importer 1.62.0-3<1.62.0-5
1.62.0-5
Microsoft azl3 cert-manager 1.12.15-6<1.12.15-8
1.12.15-8
Microsoft azl3 azurelinux-image-tools 1.2.0-2<1.3.0-2
1.3.0-2
Microsoft azl3 influxdb 2.7.5-15<2.7.5-17
2.7.5-17
Microsoft azl3 kubevirt 1.7.1-2<1.7.1-5
1.7.1-5
Microsoft azl3 kube-vip-cloud-provider 0.0.10-5<0.0.10-6
0.0.10-6
Microsoft azl3 kata-containers 3.19.1.kata3-1<3.19.1.kata3-3
3.19.1.kata3-3
Microsoft azl3 application-gateway-kubernetes-ingress 1.7.7-3<1.7.7-4
1.7.7-4
Microsoft azl3 skopeo 1.14.4-10<1.14.4-11
1.14.4-11
Microsoft azl3 keda 2.14.1-11<2.14.1-13
2.14.1-13
Microsoft azl3 telegraf 1.31.0-19<1.31.0-21
1.31.0-21
Microsoft azl3 opa 0.63.0-3<0.63.0-4
0.63.0-4
Microsoft azl3 multus 4.0.2-7<4.0.2-8
4.0.2-8
Microsoft azl3 kata-containers-cc 3.15.0.aks0-9<3.15.0.aks0-11
3.15.0.aks0-11
Microsoft azl3 jx 3.10.182-3<3.10.182-4
3.10.182-4
Microsoft azl3 prometheus-process-exporter 0.8.2-3<0.8.2-4
0.8.2-4
Microsoft azl3 flannel 0.24.2-26<0.24.2-28
0.24.2-28
Microsoft azl3 ignition-flatcar 2.22.0-2<2.22.0-3
2.22.0-3
Microsoft azl3 gh 2.62.0-15<2.62.0-16
2.62.0-16
Microsoft azl3 containerd2 2.1.6-2<2.1.6-3
2.1.6-3
Microsoft azl3 cloud-provider-kubevirt 0.5.1-3<0.5.1-4
0.5.1-4
Microsoft azl3 coredns 1.11.4-15<1.11.4-17
1.11.4-17
Microsoft azl3 docker-cli 25.0.7-2<25.0.7-3
25.0.7-3
Microsoft azl3 azcopy 10.25.1-4<10.25.1-5
10.25.1-5
Microsoft azl3 docker-compose 2.27.0-9<2.27.0-11
2.27.0-11
Microsoft azl3 docker-buildx 0.14.0-11<0.14.0-13
0.14.0-13
Microsoft azl3 cf-cli 8.7.11-5<8.7.11-6
8.7.11-6
IBM Db2 Genius Hub<=1.1, 1.1.1, 1.1.2
IBM Agentics<=1.0

Remediation

Recommended actions to resolve this vulnerability, in priority order.

  1. Upgrade

    Upgrade debian/golang-golang-x-net to a version that resolves this vulnerability.

    Fixed in 1:0.55.0-1
  2. Upgrade

    Upgrade to a fixed release to a version that resolves this vulnerability.

    Fixed in 3.7.0-6
  3. Upgrade

    Upgrade to a fixed release to a version that resolves this vulnerability.

    Fixed in 19.0.4-10
  4. Upgrade

    Upgrade to a fixed release to a version that resolves this vulnerability.

    Fixed in 1.25.11-2
  5. Upgrade

    Upgrade to a fixed release to a version that resolves this vulnerability.

    Fixed in 25.0.3-18
  6. Upgrade

    Upgrade to a fixed release to a version that resolves this vulnerability.

    Fixed in 1.30.10-25
  7. Upgrade

    Upgrade to a fixed release to a version that resolves this vulnerability.

    Fixed in 3.6.1-3
  8. Upgrade

    Upgrade to a fixed release to a version that resolves this vulnerability.

    Fixed in 1.7.7-13
  9. Upgrade

    Upgrade to a fixed release to a version that resolves this vulnerability.

    Fixed in 3.15.0.aks0-11
  10. Upgrade

    Upgrade to a fixed release to a version that resolves this vulnerability.

    Fixed in 1.26.4-2
  11. Upgrade

    Upgrade to a fixed release to a version that resolves this vulnerability.

    Fixed in 0.12.0-6
  12. Upgrade

    Upgrade to a fixed release to a version that resolves this vulnerability.

    Fixed in 1.7.0-4
  13. Upgrade

    Upgrade to a fixed release to a version that resolves this vulnerability.

    Fixed in 3.19.1.kata3-3
  14. Upgrade

    Upgrade to a fixed release to a version that resolves this vulnerability.

    Fixed in 1.9.5-14
  15. Upgrade

    Upgrade to a fixed release to a version that resolves this vulnerability.

    Fixed in 1.15.0-5
  16. Upgrade

    Upgrade to a fixed release to a version that resolves this vulnerability.

    Fixed in 3.5.30-2
  17. Upgrade

    Upgrade to a fixed release to a version that resolves this vulnerability.

    Fixed in 1.62.0-5
  18. Upgrade

    Upgrade to a fixed release to a version that resolves this vulnerability.

    Fixed in 1.12.15-8
  19. Upgrade

    Upgrade to a fixed release to a version that resolves this vulnerability.

    Fixed in 1.32.0-6
  20. Upgrade

    Upgrade to a fixed release to a version that resolves this vulnerability.

    Fixed in 1.3.0-2
  21. Upgrade

    Upgrade to a fixed release to a version that resolves this vulnerability.

    Fixed in 2.7.5-17
  22. Upgrade

    Upgrade to a fixed release to a version that resolves this vulnerability.

    Fixed in 1.7.1-5
  23. Upgrade

    Upgrade to a fixed release to a version that resolves this vulnerability.

    Fixed in 0.0.10-6
  24. Upgrade

    Upgrade to a fixed release to a version that resolves this vulnerability.

    Fixed in 2.14.1-13
  25. Upgrade

    Upgrade to a fixed release to a version that resolves this vulnerability.

    Fixed in 1.14.4-11
  26. Upgrade

    Upgrade to a fixed release to a version that resolves this vulnerability.

    Fixed in 1.7.7-4
  27. Upgrade

    Upgrade to a fixed release to a version that resolves this vulnerability.

    Fixed in 0.63.0-4
  28. Upgrade

    Upgrade to a fixed release to a version that resolves this vulnerability.

    Fixed in 4.0.2-8
  29. Upgrade

    Upgrade to a fixed release to a version that resolves this vulnerability.

    Fixed in 1.31.0-21
  30. Upgrade

    Upgrade to a fixed release to a version that resolves this vulnerability.

    Fixed in 0.8.2-4
  31. Upgrade

    Upgrade to a fixed release to a version that resolves this vulnerability.

    Fixed in 3.10.182-4
  32. Upgrade

    Upgrade to a fixed release to a version that resolves this vulnerability.

    Fixed in 0.24.2-28
  33. Upgrade

    Upgrade to a fixed release to a version that resolves this vulnerability.

    Fixed in 2.22.0-3
  34. Upgrade

    Upgrade to a fixed release to a version that resolves this vulnerability.

    Fixed in 2.1.6-3
  35. Upgrade

    Upgrade to a fixed release to a version that resolves this vulnerability.

    Fixed in 2.62.0-16
  36. Upgrade

    Upgrade to a fixed release to a version that resolves this vulnerability.

    Fixed in 25.0.7-3
  37. Upgrade

    Upgrade to a fixed release to a version that resolves this vulnerability.

    Fixed in 1.11.4-17
  38. Upgrade

    Upgrade to a fixed release to a version that resolves this vulnerability.

    Fixed in 0.5.1-4
  39. Upgrade

    Upgrade to a fixed release to a version that resolves this vulnerability.

    Fixed in 2.27.0-11
  40. Upgrade

    Upgrade to a fixed release to a version that resolves this vulnerability.

    Fixed in 10.25.1-5
  41. Upgrade

    Upgrade to a fixed release to a version that resolves this vulnerability.

    Fixed in 8.7.11-6
  42. Upgrade

    Upgrade to a fixed release to a version that resolves this vulnerability.

    Fixed in 0.14.0-13

Event History

May 22, 2026
CVE Published
via MITRE·03:01 PM
Data Sourced
via MITRE·03:01 PM
DescriptionWeakness
Data Sourced
via Red Hat·04:01 PM
DescriptionSeverityAffected Software
Data Sourced
via NVD·04:16 PM
DescriptionSeverityWeaknessAffected Software
May 27, 2026
Data Sourced
via Microsoft·08:03 AM
DescriptionSeverityWeaknessAffected Software
Updated
via Microsoft·08:03 AM
Affected Software
Updated
via Microsoft·08:03 AM
SeverityAffected Software
Updated
via Microsoft·08:03 AM
DescriptionSeverityWeakness
Updated
via Microsoft·08:03 AM
DescriptionSeverity
Jun 9, 2026
Data Sourced
via Launchpad·08:09 PM
Description
Jun 10, 2026
Data Sourced
via Ubuntu·08:08 PM
RemedyDescriptionSeverityAffected Software
Data Sourced
via Debian·08:09 PM
DescriptionAffected Software
Jul 13, 2026
Data Sourced
via IBM·12:00 AM
DescriptionAffected Software

Parent advisories

This vulnerability appears in the following advisories.

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Frequently Asked Questions

1

What is the severity of CVE-2026-39821?

CVE-2026-39821 has a risk rating of 51, indicating a moderate severity level.

2

How do I fix CVE-2026-39821?

To fix CVE-2026-39821, update to the latest version of golang.org/x/net/idna that addresses this vulnerability.

3

What impact does CVE-2026-39821 have on my applications?

CVE-2026-39821 may lead to privilege escalation due to improper validation of Punycode-encoded labels in applications utilizing the affected IDNA functions.

4

What specific functions are affected by CVE-2026-39821?

The ToASCII and ToUnicode functions in golang.org/x/net/idna are affected by CVE-2026-39821.

5

Are there any known exploits for CVE-2026-39821?

As of now, there are no public exploits reported for CVE-2026-39821, but its presence may offer risk in vulnerable applications.

Company

Resources

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