cvedb.io
CVE-2026-39821
CRITICAL · CVSS 9.6
EPSS exploitation probability: 0%
Published 2026-05-22T16:16:20.410 · Last modified 2026-07-02T12:17:12.240

Summary

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".

Affected products

golang — net

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References

This product uses data from the NVD API but is not endorsed or certified by the NVD. Informational only; not professional security advice.