CVE-2026-39821

CRITICAL EPSS 26.3%
Published May 22, 20261mo ago · Modified Jun 17, 20261w ago
9.6 CVSS 3.1
Critical
Find Similar
Published May 22, 2026 1mo ago
Last Modified Jun 17, 2026 1w ago

Description

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".

CVSS Details

Base Score
9.6
Exploitability
3.1
Impact
5.8
Vector string
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:N
Attack Vector Network
Attack Complexity Low
Privileges Required Low
User Interaction None
Scope Changed
Confidentiality High
Integrity High
Availability None

Threat Intelligence

EPSS Exploit Probability
26.3% percentile
Exploit & Patch Status
No Known Exploit
No Patch Available

Weaknesses 1

CWE-1289

Affected Products 1

VendorProductVersionRange
golangnet* <0.55.0

References 4

  • go.dev https://go.dev/cl/767220
    Issue Tracking
  • go.dev https://go.dev/issue/78760
    Issue Tracking
  • groups.google.com https://groups.google.com/g/golang-announce/c/iI-mYSI0lu8
    Mailing List
  • pkg.go.dev https://pkg.go.dev/vuln/GO-2026-5026
    Vendor Advisory

Remediation

No remediation data recorded yet

Check vendor advisories and the NVD entry for patch availability.