CVE & CISA-KEV Catalog

CVE-2026-39821

CRITICAL

10.0

CVSS v3

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".

How to fix

Remediation Available

containerdAmazon

Fixed in:0:2.2.4-1.amzn2023.0.2

Fixed in:0:2.2.4-1.amzn2023.0.2

containerd-debuginfoAmazon

Fixed in:0:2.2.4-1.amzn2023.0.2

Fixed in:0:2.2.4-1.amzn2023.0.2

containerd-debugsourceAmazon

Fixed in:0:2.2.4-1.amzn2023.0.2

Fixed in:0:2.2.4-1.amzn2023.0.2

containerd-stressAmazon

Fixed in:0:2.2.4-1.amzn2023.0.2

Fixed in:0:2.2.4-1.amzn2023.0.2

containerd-stress-debuginfoAmazon

Fixed in:0:2.2.4-1.amzn2023.0.2

Fixed in:0:2.2.4-1.amzn2023.0.2

credentials-fetcherAmazon

Fixed in:0:2.0.3-1.amzn2023.0.1

Fixed in:0:2.0.3-1.amzn2023.0.1

dockerAmazon

Fixed in:0:25.0.16-1.amzn2023.0.2

Fixed in:0:25.0.16-1.amzn2023.0.2

docker-debuginfoAmazon

Fixed in:0:25.0.16-1.amzn2023.0.2

Fixed in:0:25.0.16-1.amzn2023.0.2

docker-debugsourceAmazon

Fixed in:0:25.0.16-1.amzn2023.0.2

Fixed in:0:25.0.16-1.amzn2023.0.2

nerdctlAmazon

Fixed in:0:2.2.2-1.amzn2.0.3

Fixed in:0:2.2.2-1.amzn2.0.3

Fixed in:0:2.2.2-1.amzn2023.0.3

Fixed in:0:2.2.2-1.amzn2023.0.3

nerdctl-debuginfoAmazon

Fixed in:0:2.2.2-1.amzn2.0.3

Fixed in:0:2.2.2-1.amzn2.0.3

runfinch-finchAmazon

Fixed in:0:1.17.1-1.amzn2023.0.3

Fixed in:0:1.17.1-1.amzn2023.0.3

soci-snapshotterAmazon

Fixed in:0:0.14.1-1.amzn2023.0.1

Fixed in:0:0.14.1-1.amzn2023.0.1

golang-golang-x-netDebian

Fixed in:1:0.55.0-1CVE-2026-39821

golang.org/x/netGo

Fixed in:0.55.0GO-2026-5026

stdlibGo

Fixed in:1.27.0-rc.3GO-2026-5026

aap-metrics-utilityRocky

Fixed in:0:0.7.5-3.el9apRHSA-2026:42079

Fixed in:0:0.7.5-3.el9apRHSA-2026:42079

Fixed in:0:0.7.5-3.el9apRHSA-2026:42079

Fixed in:0:0.7.5-3.el9apRHSA-2026:42079

Fixed in:0:0.7.5-3.el9apRHSA-2026:42079

aap-metrics-utilityRed Hat / RHEL

Fixed in:0:0.7.5-3.el9apRHSA-2026:42079

Fixed in:0:0.7.5-3.el9apRHSA-2026:42079

Fixed in:0:0.7.5-3.el9apRHSA-2026:42079

Fixed in:0:0.7.5-3.el9apRHSA-2026:42079

Fixed in:0:0.7.5-3.el9apRHSA-2026:42079

ansible-automation-platform-installerRocky

Fixed in:0:2.6-8.1.el9apRHSA-2026:42079

Fixed in:0:2.6-8.1.el9apRHSA-2026:42079

ansible-automation-platform-installerRed Hat / RHEL

Fixed in:0:2.6-8.1.el9apRHSA-2026:42079

Fixed in:0:2.6-8.1.el9apRHSA-2026:42079

ansible-builderRed Hat / RHEL

Fixed in:0:3.1.1-3.1.el10apRHSA-2026:42080

Fixed in:0:3.1.1-3.1.el10apRHSA-2026:42080

Fixed in:0:3.1.1-3.1.el9apRHSA-2026:42080

Fixed in:0:3.1.1-3.1.el9apRHSA-2026:42080

ansible-builderRocky

Fixed in:0:3.1.1-3.1.el10apRHSA-2026:42080

Fixed in:0:3.1.1-3.1.el10apRHSA-2026:42080

Fixed in:0:3.1.1-3.1.el9apRHSA-2026:42080

Fixed in:0:3.1.1-3.1.el9apRHSA-2026:42080

ansible-coreRed Hat / RHEL

Fixed in:2:2.16.19-1.el10apRHSA-2026:42079

Fixed in:2:2.16.19-1.el10apRHSA-2026:42080

Fixed in:2:2.16.19-1.el10apRHSA-2026:42079

Fixed in:2:2.16.19-1.el10apRHSA-2026:42080

Fixed in:1:2.16.19-1.el8apRHSA-2026:42078

Fixed in:1:2.16.19-1.el8apRHSA-2026:42078

Fixed in:1:2.16.19-1.el9apRHSA-2026:42080

Fixed in:1:2.16.19-1.el9apRHSA-2026:42080

ansible-coreRocky

Fixed in:2:2.16.19-1.el10apRHSA-2026:42079

Fixed in:2:2.16.19-1.el10apRHSA-2026:42079

Fixed in:2:2.16.19-1.el10apRHSA-2026:42080

Fixed in:2:2.16.19-1.el10apRHSA-2026:42080

Fixed in:1:2.16.19-1.el8apRHSA-2026:42078

Fixed in:1:2.16.19-1.el8apRHSA-2026:42078

Fixed in:1:2.16.19-1.el9apRHSA-2026:42079

Fixed in:1:2.16.19-1.el9apRHSA-2026:42079

ansible-creatorRed Hat / RHEL

Fixed in:0:26.6.1-1.el10apRHSA-2026:42079

Fixed in:0:26.6.1-2.el10apRHSA-2026:42080

Fixed in:0:26.6.1-2.el10apRHSA-2026:42080

Fixed in:0:26.6.1-1.el10apRHSA-2026:42079

Fixed in:0:26.6.1-2.el9apRHSA-2026:42080

Fixed in:0:26.6.1-1.el9apRHSA-2026:42079

Fixed in:0:26.6.1-1.el9apRHSA-2026:42079

Fixed in:0:26.6.1-2.el9apRHSA-2026:42080

ansible-creatorRocky

Fixed in:0:26.6.1-2.el10apRHSA-2026:42080

Fixed in:0:26.6.1-1.el10apRHSA-2026:42079

Fixed in:0:26.6.1-1.el10apRHSA-2026:42079

Fixed in:0:26.6.1-2.el10apRHSA-2026:42080

Fixed in:0:26.6.1-1.el9apRHSA-2026:42079

Fixed in:0:26.6.1-2.el9apRHSA-2026:42080

Fixed in:0:26.6.1-2.el9apRHSA-2026:42080

Fixed in:0:26.6.1-1.el9apRHSA-2026:42079

ansible-dev-environmentRocky

Fixed in:0:26.6.1-1.el10apRHSA-2026:42080

Fixed in:0:26.6.1-1.el10apRHSA-2026:42079

Fixed in:0:26.6.1-1.el10apRHSA-2026:42080

Fixed in:0:26.6.1-1.el10apRHSA-2026:42079

Fixed in:0:26.6.1-1.el9apRHSA-2026:42080

Fixed in:0:26.6.1-1.el9apRHSA-2026:42079

Fixed in:0:26.6.1-1.el9apRHSA-2026:42079

Fixed in:0:26.6.1-1.el9apRHSA-2026:42080

ansible-dev-environmentRed Hat / RHEL

Fixed in:0:26.6.1-1.el10apRHSA-2026:42079

Fixed in:0:26.6.1-1.el10apRHSA-2026:42079

Fixed in:0:26.6.1-1.el10apRHSA-2026:42080

Fixed in:0:26.6.1-1.el10apRHSA-2026:42080

Fixed in:0:26.6.1-1.el9apRHSA-2026:42079

Fixed in:0:26.6.1-1.el9apRHSA-2026:42079

Fixed in:0:26.6.1-1.el9apRHSA-2026:42080

Fixed in:0:26.6.1-1.el9apRHSA-2026:42080

ansible-dev-toolsRed Hat / RHEL

Fixed in:0:26.7.1-1.el10apRHSA-2026:42079

Fixed in:0:26.7.1-1.el10apRHSA-2026:42079

Fixed in:0:26.7.1-1.el10apRHSA-2026:42080

Fixed in:0:26.7.1-1.el10apRHSA-2026:42080

Fixed in:0:26.7.1-1.el9apRHSA-2026:42080

Fixed in:0:26.7.1-1.el9apRHSA-2026:42079

Fixed in:0:26.7.1-1.el9apRHSA-2026:42080

Fixed in:0:26.7.1-1.el9apRHSA-2026:42079

ansible-dev-toolsRocky

Fixed in:0:26.7.1-1.el10apRHSA-2026:42079

Fixed in:0:26.7.1-1.el10apRHSA-2026:42080

Fixed in:0:26.7.1-1.el10apRHSA-2026:42079

Fixed in:0:26.7.1-1.el10apRHSA-2026:42080

Fixed in:0:26.7.1-1.el9apRHSA-2026:42079

Fixed in:0:26.7.1-1.el9apRHSA-2026:42080

Fixed in:0:26.7.1-1.el9apRHSA-2026:42079

Fixed in:0:26.7.1-1.el9apRHSA-2026:42080

This vulnerability affects an unusually large number of packages. The highest-confidence fixes are shown above; the full list is longer. Check the referenced advisories for complete coverage.

TridentStack Control can deploy fixes like this automatically across your Windows, macOS, and Linux fleet. See how it works

Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.

CVSS v3 Vector

Exploitability

Attack VectorNetwork

Attack ComplexityLow

Privileges RequiredNone

User InteractionNone

ScopeChanged

Impact

ConfidentialityHigh

IntegrityHigh

AvailabilityNone

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:N/E:U

Exploit Intelligence

0.69%probability of exploitation in 30 days

51stpercentile

Moderate risk: more likely to be exploited than 51% of all known CVEs.

References

Vendor Advisory1

pkg.go.dev

Issue Tracking2

Mailing List1

groups.google.com

Other references46

Related Vulnerabilities

Other CWE-1289 vulnerabilities, ordered by exploit likelihood. View all

CVE	Severity	CVSS	EPSS	Exploited	Fix
CVE-2026-48710	Medium	6.5	36%	KEV	Fix
CVE-2024-45179	High	7.2	2.6%	-	-
CVE-2026-47729	Medium	6.5	1.5%	-	Fix
CVE-2025-62718	Critical	9.9	1.2%	-	Fix
CVE-2026-33515	Medium	5.3	1.0%	-	Fix
CVE-2022-0675	Medium	5.6	0.9%	-	Fix

Common questions

How do I fix CVE-2026-39821?

Published advisories record a fix for 427 affected products. The "How to fix" section on this page lists the fixed version and source advisory for each one, so apply the entry matching what you actually run.

Is CVE-2026-39821 being actively exploited?

Not that we know of. CVE-2026-39821 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 0.69% is the estimated probability that it will be exploited in the next 30 days. That is higher than 51% of all scored CVEs.

How severe is CVE-2026-39821?

CVE-2026-39821 has a CVSS v3 base score of 10.0, rated critical. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.

What does CVE-2026-39821 affect?

Published advisories record a fix for containerd (Amazon), containerd-debuginfo (Amazon), containerd-debugsource (Amazon), containerd-stress (Amazon), and 423 more. The list on this page is capped, so there may be more.

Embed a live status badge for CVE-2026-39821

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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-09-17.