CVE-2026-39821
Published: May 28, 2026Last modified: May 29, 2026
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".
Severity score breakdown
| Parameter | Value |
|---|---|
| Base score | 9.6 |
| Attack Vector | NETWORK |
| Attack complexity | LOW |
| Privileges required | LOW |
| User interaction | NONE |
| Scope | CHANGED |
| Confidentiality | HIGH |
| Integrity impact | HIGH |
| Availability impact | NONE |
| Vector | CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:N |
Status
| Product | Release | Package | Status |
|---|---|---|---|
| Alpaquita Linux | 23 LTS | buildah | Vulnerable (1.28.0-r1) |
| containerd | Vulnerable (1.6.10-r0) | ||
| podman | Vulnerable (4.3.1-r0) | ||
| runc | Vulnerable (1.1.4-r3) | ||
| skopeo | Vulnerable (1.10.0-r2) | ||
| 25 LTS | buildah | Vulnerable (1.40.0-r0) | |
| containerd | Vulnerable (2.1.1-r0) | ||
| docker-cli-buildx | Vulnerable (0.24.0-r0) | ||
| google-guest-agent | Vulnerable (20250521.00-r0) | ||
| osv-scanner | Vulnerable (2.1.0-r4) | ||
| podman | Vulnerable (5.5.0-r0) | ||
| rootlesskit | Vulnerable (2.3.5-r0) | ||
| runc | Vulnerable (1.3.0-r1) | ||
| skopeo | Vulnerable (1.18.0-r2) | ||
| Stream | buildah | Vulnerable (1.31.0-r0) | |
| calicoctl | Vulnerable (3.31.3-r0) | ||
| cilium-cli | Vulnerable (0.19.0-r12) | ||
| cni-plugins | Vulnerable (1.9.0-r2) | ||
| containerd | Vulnerable (1.7.2-r1) | ||
| cri-tools | Vulnerable (1.35.0-r2) | ||
| docker-cli-buildx | Vulnerable (0.11.0-r0) | ||
| etcd | Vulnerable (3.6.4-r6) | ||
| google-guest-agent | Vulnerable (20250214.01-r0) | ||
| grype | Vulnerable (0.100.0-r0) | ||
| helm | Vulnerable (3.19.0-r4) | ||
| osv-scanner | Vulnerable (2.1.0-r2) | ||
| podman | Vulnerable (4.5.1-r1) | ||
| rootlesskit | Vulnerable (2.1.0-r0) | ||
| runc | Vulnerable (1.1.7-r1) | ||
| skopeo | Vulnerable (1.13.0-r1) |