CVE-2026-126348: Input Validation Flaw (CVSS 4.3)

Description

Addressable is an alternative implementation to the URI implementation that is part of Ruby's standard library. From 2.0.0 until 2.9.1, the pure-Ruby Addressable::IDNA.to_unicode implementation decodes invalid Punycode A-labels instead of returning them unchanged. Labels that decode to ASCII text or fail to convert back to the same A-label can therefore make Addressable::URI#display_uri show a trusted-looking host while host, normalized_host, and the connection target retain the attacker-controlled encoded host. A trusted-name comparison using Addressable::IDNA.to_unicode output can also treat two different hosts as the same without displaying the URI. The native libidn implementation, to_ascii, and normalized_host are unaffected. This issue is fixed in version 2.9.1.

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CVSS v3.1 Score

4.3

MEDIUM

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

Weakness Type (CWE)

CWE-20 Improper Input Validation

CWE-1007 CWE-1007

References

Other References

https://github.com/sporkmonger/addressable/commit/b8a59cc0e03f8704f1d7c8122fc8f7ef8548362d https://github.com/sporkmonger/addressable/releases/tag/addressable-2.9.1 https://github.com/sporkmonger/addressable/security/advisories/GHSA-9crm-g4mf-wc5j

Frequently Asked Questions

What is CVE-2026-126348? +

Addressable is an alternative implementation to the URI implementation that is part of Ruby's standard library. From 2.0.0 until 2.9.1, the pure-Ruby Addressable::IDNA.to_unicode implementation decodes invalid Punycode A-labels instead of returning them unchanged. Labels that decode to ASCII text or fail to convert back to the same A-label can therefore make Addressable::URI#display_uri show a trusted-looking host while host, normalized_host, and the connection target retain the attacker-controlled encoded host. A trusted-name comparison using Addressable::IDNA.to_unicode output can also treat two different hosts as the same without displaying the URI. The native libidn implementation, to_ascii, and normalized_host are unaffected. This issue is fixed in version 2.9.1. It has a CVSS v3.1 base score of 4.3 (MEDIUM).

How severe is CVE-2026-126348? +

CVE-2026-126348 has a CVSS v3.1 score of 4.3 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance.

How do I check if I'm vulnerable to CVE-2026-126348? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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