CVE-2026-126080 Active Support: Possible DoS vulnerability in Active Support safe_constantize
- Exploited in the wild
- Not known
- Fix
- Available
What is CVE-2026-126080?
CVE-2026-126080 is a high-severity vulnerability in rails, published on 10 Nov 2026.
Official description
Active Support is a collection of utility classes and standard library extensions used by Rails and other Ruby projects. Prior to 8.1.4.1 and 8.0.5.2, when constant lookup raises LoadError, ActiveSupport::Inflector#safe_constantize (and String#safe_constantize) builds a regular expression from the requested constant name without escaping it, so a caller that passes untrusted input lets the attacker choose the source of a pattern that the application compiles. Crafted patterns can trigger defects in Ruby's regular expression compiler, possibly leading to a crash of the server process, and repeated requests could keep the application unavailable. Action Cable passes the channel value of each subscribe command to safe_constantize before any channel lookup, so an unauthenticated client can reach this code when the application mounts Action Cable and accepts connections from untrusted clients without an added authentication check. This issue is fixed in versions 8.1.4.1 and 8.0.5.2.
Weakness: CWE-74
Which versions are affected by CVE-2026-126080?
2 open source packages ship an affected version, including activesupport.
| Package | Affected | Fixed in |
|---|---|---|
activesupport RubyGems | All versions | 8.0.5.2 |
activesupport RubyGems | From 8.1.0.beta1 | 8.1.4.1 |
How do I fix CVE-2026-126080?
Upgrade activesupport to a fixed version for your release line: 8.0.5.2 or 8.1.4.1.
Is CVE-2026-126080 being exploited?
There is no known exploitation of CVE-2026-126080 in the wild and no public exploit code.
Sources
Also known as DEBIAN-CVE-2026-126080, GHSA-8474-xrp6-wh69, UBUNTU-CVE-2026-126080.