9.6 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 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".
https://nvd.nist.gov/vuln/detail/CVE-2026-39821

Categories

CWE-1289 : Improper Validation of Unsafe Equivalence in Input
The product receives an input value that is used as a resource identifier or other type of reference, but it does not validate or incorrectly validates that the input is equivalent to a potentially-unsafe value. Chain: A microservice integration and management platform compares the hostname in the HTTP Host header in a case-sensitive way (CWE-178, CWE-1289), allowing bypass of the authorization policy (CWE-863) using a hostname with mixed case or other variations. Chain: Go-based Oauth2 reverse proxy can send the authenticated user to another site at the end of the authentication flow. A redirect URL with HTML-encoded whitespace characters can bypass the validation (CWE-1289) to redirect to a malicious site (CWE-601) File extension check in forum software only verifies extensions that contain all lowercase letters, which allows remote attackers to upload arbitrary files via file extensions that include uppercase letters. Task Manager does not allow local users to end processes with uppercase letters named (1) winlogon.exe, (2) csrss.exe, (3) smss.exe and (4) services.exe via the Process tab which could allow local users to install Trojan horses that cannot be stopped. HTTP server allows bypass of access restrictions using URIs with mixed case.

References

 

AFFECTED (from MITRE)

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Vendor	Product	Versions
golang.org/x/net	golang.org/x/net/idna	< 0.55.0 [affected]
© 2022 The MITRE Corporation. This work is reproduced and distributed with the permission of The MITRE Corporation.

CPE

cpe	start	end
Configuration 1
cpe:2.3:a:golang:net:*:*:*:*:*:go:*:*		< 0.55.0

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REMEDIATION

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EXPLOITS

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Exploit-db.com

id	description	date
No known exploits

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POC Github

Url
No known exploits

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Other Nist (github, ...)

Url
No known exploits

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CAPEC

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Common Attack Pattern Enumerations and Classifications

id	description	severity
No entry

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