CVE-2026-126348 Addressable display_uri can show misleading hosts with invalid Punycode A-labels
Attackers can craft hosts with invalid Punycode A-labels that make Addressable show a trusted host, enabling phishing in Ruby apps relying on it.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Harmful if only installed
- No
- Needs a specific call
- Yes
- Fix
- Available
What is CVE-2026-126348?
CVE-2026-126348 is a medium-severity security feature bypass vulnerability in sporkmonger addressable, published on 12 Nov 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Official 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.
Which versions are affected by CVE-2026-126348?
1 open source package ship an affected version, including addressable.
An affected version is only exploitable if your software calls Addressable::IDNA.to_unicode or Addressable::URI#display_uri. Many projects that include it are not exposed.
| Package | Affected | Fixed in |
|---|---|---|
addressable RubyGems | From 2.0.0 | 2.9.1 |
How do I fix CVE-2026-126348?
Upgrade addressable to 2.9.1 or later.
Upgrade to the fixed version, and do not rely on a single control for protection. More about Security feature bypass.
Is CVE-2026-126348 being exploited?
There is no known exploitation of CVE-2026-126348 in the wild and no public exploit code.
Sources
Also known as GHSA-9crm-g4mf-wc5j.