SECUFOCUSNOW
Home›CVE index›CVE-2026-39821
Review reviewCritical

CVE-2026-39821

golang.org/x/net golang.org/x/net/idna, Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 8

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
9.6
EPSS
0.66%
47.9% percentile
CISA KEV
Not listed
Published
2026.05.23
PRIORITY ASSESSMENT

Review review

The CVSS severity warrants an early asset and exposure review.

Known exploitationNot established by KEV
Exploit probability0.66%
Technical severityCVSS 9.6

Vulnerability overview

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 product and versions

Product
golang.org/x/net golang.org/x/net/idna, Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 8
Affected versions
< 0.55.0
Fixed versions
0.55.0

Recommended response sequence

Confirm exposure before applying a vendor-supported change.

Full remediation guide
  1. 1
    Identify

    Confirm that golang.org/x/net golang.org/x/net/idna, Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 8 and an affected version are present.

  2. 2
    Prioritize

    Combine exploitation signals with asset exposure and business criticality.

  3. 3
    Remediate

    Follow the vendor advisory or supported update path and preserve rollback options.

  4. 4
    Verify

    Recheck the version, service health, access paths, and relevant logs.

Technical data

CVSS vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:N
CWE
CWE-1289
CVE-2026-39821 — golang.org/x/net golang.org/x/net/idna, Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 8 | SECUFOCUS NOW