CVE
CVE-2026-39821
Invoking failure to reject ASCII-only Punycode-encoded labels in golang.org/x/net/idna
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".
Package Versions Affected
Package Version
patch Availability
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CVSS Version
Severity
Base Score
CVSS Version
Score Vector
C
H
U
9.6
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3.1
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:N
C
H
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0
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C
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U
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Related Resources
No items found.
References
https://go.dev/cl/767220, https://go.dev/issue/78760, https://groups.google.com/g/golang-announce/c/iI-mYSI0lu8
Basic Information
Ecosystem
