CVE-2026-39821
Published:May 22, 2026
Updated:May 25, 2026
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 Packages
https://github.com/golang/net.git (GITHUB):
Affected version(s) >=v0.1.0 <v0.55.0Fix Suggestion:
Update to version v0.55.0golang.org/x/net (GO):
Affected version(s) >=v0.0.0-20120125194513-f61fbb80d2fc <v0.55.0Fix Suggestion:
Update to version v0.55.0Related Resources (4)
Do you need more information?
Contact UsCVSS v4
Base Score:
9.9
Attack Vector
NETWORK
Attack Complexity
LOW
Attack Requirements
NONE
Privileges Required
NONE
User Interaction
NONE
Vulnerable System Confidentiality
HIGH
Vulnerable System Integrity
HIGH
Vulnerable System Availability
NONE
Subsequent System Confidentiality
HIGH
Subsequent System Integrity
HIGH
Subsequent System Availability
NONE
CVSS v3
Base Score:
10
Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
NONE
Scope
CHANGED
Confidentiality
HIGH
Integrity
HIGH
Availability
NONE
EPSS
Base Score:
0.04