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CVE-2026-39821Published

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…

Exact source revision recorded 25 Oct 2026 09:17:18 UTC. It does not establish the source's current position. Latest evidence.

Recorded JSON

nvd · CVE-2026-39821

Published

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".

NVD analysis and CPE criteria are source context, not proof that a package or your environment is affected. Complete affected data, logical configurations and SSVC are retained in the original JSON.

Source analysis status: Modified

Weakness classifications: CWE-1289

Original publisher date fields

published: 2026-05-22T16:16:20.410

lastModified: 2026-09-17T12:18:05.767

1 source CPE criteria · context only
  • cpe:2.3:a:golang:net:*:*:*:*:*:go:*:*

The original JSON retains the logical configuration operators, exclusions and version bounds.

Source published
22 May 2026 16:16:20 UTC
Source modified
17 Sep 2026 12:18:05 UTC
Observed here
25 Oct 2026 09:17:18 UTC
Source terms
NIST NVD usage terms; underlying source attribution retained

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: nvd · NIST NVD usage terms; underlying source attribution retained. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 3.1 · 134c704f-9b21-4f2e-91b3-4a467353bcc0 · Secondary · 9.6 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:N

CVSS 3.1 · 0b0ca135-0b70-47e7-9f44-1890c2a1c46c · Secondary · 8.2 CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:N

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Sources read 9 Nov 10:47 UTC · 275 of 275 readable · 273 fully read · documentation 469/469 current

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