Open-Source Security Intelligence

Know every vulnerability
before it knows you.

DevGuard continuously monitors your dependencies and alerts you when CVEs like this one affect your stack — with real-time threat intelligence built for developers.

Check if your repositories are affected!View on GitHub
Search

GHSA-9crm-g4mf-wc5j

MediumCVSS 4.3 / 10
Published Nov 12, 2026·Last modified Nov 12, 2026
Affected Components(1)
RubyGems logoaddressable
2.0.0 – 2.9.1
Description

Impact

Addressable::IDNA.to_unicode, in the pure-Ruby IDNA implementation, decodes Punycode labels (labels beginning with xn--) that are not valid A-labels. Those labels are returned in decoded form, when they should be returned unchanged. That includes:

  • labels that decode to only ASCII characters, e.g. xn--google- decodes to google;
  • labels that decode to text that doesn't convert back to the same label (RFC 3490 §4.2), e.g. text that isn't in normalized form.

Addressable::URI#display_uri uses to_unicode, so for https://xn--google-.example.org/ it displays the host google.example.org, while #host, #normalized_host and any connection made from the URI use xn--google-.example.org. An attacker who controls a domain can therefore have a URI displayed as a host they don't control. Applications that compare the result of to_unicode against a list of trusted names can likewise treat two different hosts as the same.

The native IDNA implementation, used when libidn and the idn-ruby gem are installed, is not affected. to_ascii and normalized_host are not affected.

Affected Versions

This vulnerability affects Addressable >= 2.0.0, the first version with the pure-Ruby IDNA implementation, when that implementation is in use. It is fixed in 2.9.1, where such labels are returned unchanged, as with libidn.

Workarounds

  • Install libidn and the idn-ruby gem, so that Addressable uses the native IDNA implementation.
  • Don't make security decisions on display_uri or to_unicode output. Compare hosts using normalized_host.

Credits

Reported by @tonghuaroot.

For more information

If there are any questions or comments about this advisory:

Upload your SBOM

Upload your own SBOM in CycloneDX 1.6 or higher (JSON) directly here to check your vulnerabilities.

Risk Scores
Base Score
4.3

The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker does not need any special privileges or access rights. The attacker needs the user to perform some action, like clicking a link. The impact is confined to the system where the vulnerability exists. There is a low impact on the integrity of the data.

Threat Intelligence
4.0

Exploitation attempts have been detected. Elevated vigilance and prompt remediation are advised.

EPSS
0.27%

The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.

Exploit
Not available

We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.

Related Vulnerabilities

Browse More

Medium severity
Scan your project

Continuously monitor your dependencies and get alerted when vulnerabilities like this one affect your stack.

Checkout DevGuard