CVE-2026-39821
9.6 · CRITICALOverview
CVE-2026-39821 is a critical-severity vulnerability affecting golang net. It was published on May 22, 2026 and has a CVSS 3.1 base score of 9.6 (CRITICAL).
This vulnerability has a CVSS 3.1 base score of 9.6, rated CRITICAL. It can be exploited remotely over the network. Some level of privileges is required for exploitation.
Technical 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".
Remediation
Check the references section for vendor advisories and patches from golang. Update net to the latest patched version. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.
Affected Products
| Vendor | Product | Versions | Status |
|---|---|---|---|
| golang | net | >= 0, < 0.55.0 | Affected |
References
Frequently Asked Questions
What is CVE-2026-39821?
CVE-2026-39821 is a critical-severity vulnerability affecting golang net. It was published on May 22, 2026 and has a CVSS 3.1 base score of 9.6 (CRITICAL).
How severe is CVE-2026-39821?
This vulnerability has a CVSS 3.1 base score of 9.6, rated CRITICAL. It can be exploited remotely over the network. Some level of privileges is required for exploitation.
How do I fix or remediate CVE-2026-39821?
Check the references section for vendor advisories and patches from golang. Update net to the latest patched version. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.
How can CyberStrike help with CVE-2026-39821?
CyberStrike's AI-powered security agents can automatically detect CVE-2026-39821 across your infrastructure using autonomous pentesting, DAST scanning, and HackBrowser. The platform continuously monitors for known vulnerabilities and provides actionable remediation guidance prioritized by real-world exploitability.
How CyberStrike Helps
AI agents map your attack surface to find vulnerabilities like this one.
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