# CVE-2026-126080: Active Support: Possible DoS vulnerability in Active Support safe_constantize


- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Fix available:** Yes
- **Published:** 10 Nov 2026
- **Updated:** 12 Nov 2026
- **Also known as:** DEBIAN-CVE-2026-126080, GHSA-8474-xrp6-wh69, UBUNTU-CVE-2026-126080

## 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 (Improper Neutralization of Special Elements in Output Used by a Downstream Component)

## Which versions are affected by CVE-2026-126080?

2 open source packages ship an affected version, including activesupport.


| Package | Ecosystem | 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.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-126080 and fix it if it is affected.

What it is: CVE-2026-126080 is a high-severity vulnerability in rails, published on 10 Nov 2026. 
Exploitation: There is no known exploitation of CVE-2026-126080 in the wild and no public exploit code.

Affected packages and fixed versions:
- activesupport (RubyGems): affected all versions; fixed in 8.0.5.2
- activesupport (RubyGems): affected from 8.1.0.beta1; fixed in 8.1.4.1

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-126080/ (Markdown: https://insights.sbomify.com/CVE-2026-126080/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-126080
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-126080
- OSV: https://osv.dev/vulnerability/CVE-2026-126080

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-126080/
Summaries are generated and may contain mistakes; the official description above is the record.