What is CVE-2026-39821?

CVE-2026-39821 is a critical-severity vulnerability in Golang Net, classified under CWE-1289. CVSS score: 9.6/10. Published 2026-05-22.

How severe is CVE-2026-39821?

Critical severity. CVSS v3 base score is 9.6 out of 10.

Vulnerability in Golang Net

CVE-2026-39821

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 ca…

EPSS: 0.001 (16.1th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 9.6 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:N.

Affected products

Golang Net
Golang.org/x/net Golang.org/x/net/idna — versions 0

Weakness classification (CWE)

CWE-1289

References

security@golang.org (Issue Tracking)
security@golang.org (Issue Tracking)
security@golang.org (Mailing List)
security@golang.org (Vendor Advisory)

Frequently asked questions

What is CVE-2026-39821?: CVE-2026-39821 is a critical-severity vulnerability in Golang Net, classified under CWE-1289. CVSS score: 9.6/10. Published 2026-05-22.
How severe is CVE-2026-39821?: Critical severity. CVSS v3 base score is 9.6 out of 10.