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NVD Vulnerability Details :
CVE-2026-39821
Modified
More InfoOfficial Page
Source-security@golang.org
View Known Exploited Vulnerability (KEV) details
Published At-22 May, 2026 | 16:16
Updated At-17 Jul, 2026 | 13:18

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".

CISA Catalog
Date AddedDue DateVulnerability NameRequired Action
N/A
Date Added: N/A
Due Date: N/A
Vulnerability Name: N/A
Required Action: N/A
Metrics
TypeVersionBase scoreBase severityVector
Secondary3.19.6CRITICAL
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:N
Secondary3.18.2HIGH
CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:N
N/A
Type: Secondary
Version: 3.1
Base score: 9.6
Base severity: CRITICAL
Vector:
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:N
Type: Secondary
Version: 3.1
Base score: 8.2
Base severity: HIGH
Vector:
CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:N
Type: N/A
Version:
Base score:
Base severity: N/A
Vector:
CPE Matches

Go
golang
>>net>>Versions before 0.55.0(exclusive)
cpe:2.3:a:golang:net:*:*:*:*:*:go:*:*
Weaknesses
CWE IDTypeSource
CWE-1289Secondary134c704f-9b21-4f2e-91b3-4a467353bcc0
CWE-1289Secondary0b0ca135-0b70-47e7-9f44-1890c2a1c46c
CWE ID: CWE-1289
Type: Secondary
Source: 134c704f-9b21-4f2e-91b3-4a467353bcc0
CWE ID: CWE-1289
Type: Secondary
Source: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
Evaluator Description

Evaluator Impact

Evaluator Solution

Vendor Statements

References
HyperlinkSourceResource
https://go.dev/cl/767220security@golang.org
Issue Tracking
https://go.dev/issue/78760security@golang.org
Issue Tracking
https://groups.google.com/g/golang-announce/c/iI-mYSI0lu8security@golang.org
Mailing List
https://pkg.go.dev/vuln/GO-2026-5026security@golang.org
Vendor Advisory
https://access.redhat.com/errata/RHSA-2026:232620b0ca135-0b70-47e7-9f44-1890c2a1c46c
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https://access.redhat.com/errata/RHSA-2026:232640b0ca135-0b70-47e7-9f44-1890c2a1c46c
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https://access.redhat.com/errata/RHSA-2026:265460b0ca135-0b70-47e7-9f44-1890c2a1c46c
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https://access.redhat.com/errata/RHSA-2026:265470b0ca135-0b70-47e7-9f44-1890c2a1c46c
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https://access.redhat.com/errata/RHSA-2026:306500b0ca135-0b70-47e7-9f44-1890c2a1c46c
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https://access.redhat.com/errata/RHSA-2026:306510b0ca135-0b70-47e7-9f44-1890c2a1c46c
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https://access.redhat.com/errata/RHSA-2026:308530b0ca135-0b70-47e7-9f44-1890c2a1c46c
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https://access.redhat.com/errata/RHSA-2026:308540b0ca135-0b70-47e7-9f44-1890c2a1c46c
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https://access.redhat.com/errata/RHSA-2026:308550b0ca135-0b70-47e7-9f44-1890c2a1c46c
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https://access.redhat.com/errata/RHSA-2026:331550b0ca135-0b70-47e7-9f44-1890c2a1c46c
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https://access.redhat.com/errata/RHSA-2026:331600b0ca135-0b70-47e7-9f44-1890c2a1c46c
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https://access.redhat.com/errata/RHSA-2026:335240b0ca135-0b70-47e7-9f44-1890c2a1c46c
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https://access.redhat.com/errata/RHSA-2026:335310b0ca135-0b70-47e7-9f44-1890c2a1c46c
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https://access.redhat.com/errata/RHSA-2026:343420b0ca135-0b70-47e7-9f44-1890c2a1c46c
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https://access.redhat.com/errata/RHSA-2026:343570b0ca135-0b70-47e7-9f44-1890c2a1c46c
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https://access.redhat.com/errata/RHSA-2026:343590b0ca135-0b70-47e7-9f44-1890c2a1c46c
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https://access.redhat.com/errata/RHSA-2026:343640b0ca135-0b70-47e7-9f44-1890c2a1c46c
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https://access.redhat.com/errata/RHSA-2026:347890b0ca135-0b70-47e7-9f44-1890c2a1c46c
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https://access.redhat.com/errata/RHSA-2026:358260b0ca135-0b70-47e7-9f44-1890c2a1c46c
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https://access.redhat.com/errata/RHSA-2026:358270b0ca135-0b70-47e7-9f44-1890c2a1c46c
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https://access.redhat.com/errata/RHSA-2026:358280b0ca135-0b70-47e7-9f44-1890c2a1c46c
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https://access.redhat.com/errata/RHSA-2026:367960b0ca135-0b70-47e7-9f44-1890c2a1c46c
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https://access.redhat.com/errata/RHSA-2026:367970b0ca135-0b70-47e7-9f44-1890c2a1c46c
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https://access.redhat.com/errata/RHSA-2026:368080b0ca135-0b70-47e7-9f44-1890c2a1c46c
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https://access.redhat.com/errata/RHSA-2026:368200b0ca135-0b70-47e7-9f44-1890c2a1c46c
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https://access.redhat.com/errata/RHSA-2026:368830b0ca135-0b70-47e7-9f44-1890c2a1c46c
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https://access.redhat.com/errata/RHSA-2026:373870b0ca135-0b70-47e7-9f44-1890c2a1c46c
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https://access.redhat.com/errata/RHSA-2026:401180b0ca135-0b70-47e7-9f44-1890c2a1c46c
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https://access.redhat.com/errata/RHSA-2026:410300b0ca135-0b70-47e7-9f44-1890c2a1c46c
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https://access.redhat.com/errata/RHSA-2026:410660b0ca135-0b70-47e7-9f44-1890c2a1c46c
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https://access.redhat.com/security/cve/CVE-2026-398210b0ca135-0b70-47e7-9f44-1890c2a1c46c
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https://bugzilla.redhat.com/show_bug.cgi?id=24807560b0ca135-0b70-47e7-9f44-1890c2a1c46c
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https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-39821.json0b0ca135-0b70-47e7-9f44-1890c2a1c46c
N/A
Hyperlink: https://go.dev/cl/767220
Source: security@golang.org
Resource:
Issue Tracking
Hyperlink: https://go.dev/issue/78760
Source: security@golang.org
Resource:
Issue Tracking
Hyperlink: https://groups.google.com/g/golang-announce/c/iI-mYSI0lu8
Source: security@golang.org
Resource:
Mailing List
Hyperlink: https://pkg.go.dev/vuln/GO-2026-5026
Source: security@golang.org
Resource:
Vendor Advisory
Hyperlink: https://access.redhat.com/errata/RHSA-2026:23262
Source: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
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Hyperlink: https://access.redhat.com/errata/RHSA-2026:23264
Source: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
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Hyperlink: https://access.redhat.com/errata/RHSA-2026:26546
Source: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
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Hyperlink: https://access.redhat.com/errata/RHSA-2026:26547
Source: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
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Source: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
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Hyperlink: https://access.redhat.com/errata/RHSA-2026:34342
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Hyperlink: https://access.redhat.com/errata/RHSA-2026:41066
Source: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
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Hyperlink: https://access.redhat.com/security/cve/CVE-2026-39821
Source: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
Resource: N/A
Hyperlink: https://bugzilla.redhat.com/show_bug.cgi?id=2480756
Source: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
Resource: N/A
Hyperlink: https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-39821.json
Source: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
Resource: N/A
Change History
0Changes found

Details not found