# CVE-2026-126072: Action Pack: Possible DoS vulnerability in Action Controller Live streaming


- **Severity:** Medium 5.9 (`CVSS:3.1/AV:N/AC:H/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:** 10 Nov 2026
- **Also known as:** DEBIAN-CVE-2026-126072, GHSA-rwvh-fw6r-pwvp, UBUNTU-CVE-2026-126072

## What is CVE-2026-126072?

CVE-2026-126072 is a medium-severity vulnerability in rails, published on 10 Nov 2026. 

### Official description

Action Pack is a framework for handling and responding to web requests. Prior to 8.1.4.1 and 8.0.5.2, ActionController::Live::Buffer#close pushes its end-of-stream marker onto the response's bounded queue while it holds the buffer's monitor. When the client has stopped reading and the queue is full, the push blocks, and Buffer#abort, which runs when the client disconnects or a write times out, waits indefinitely for the same monitor. Each such response could permanently hold a web server thread and its ActionController::Live thread, possibly resulting in a DoS vulnerability through thread exhaustion. Applications that stream responses with ActionController::Live, including send_stream, are affected. Applications that serve large files through Active Storage proxy mode are exposed to unauthenticated clients. This issue is fixed in versions 8.1.4.1 and 8.0.5.2.

Weakness: CWE-833 (Deadlock)

## Which versions are affected by CVE-2026-126072?

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


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `actionpack` | RubyGems | All versions | 8.0.5.2 |
| `actionpack` | RubyGems | From 8.1.0.beta1 | 8.1.4.1 |

## How do I fix CVE-2026-126072?

Upgrade actionpack to a fixed version for your release line: 8.0.5.2 or 8.1.4.1.

## Is CVE-2026-126072 being exploited?

There is no known exploitation of CVE-2026-126072 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-126072 and fix it if it is affected.

What it is: CVE-2026-126072 is a medium-severity vulnerability in rails, published on 10 Nov 2026. 
Exploitation: There is no known exploitation of CVE-2026-126072 in the wild and no public exploit code.

Affected packages and fixed versions:
- actionpack (RubyGems): affected all versions; fixed in 8.0.5.2
- actionpack (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-2026-126072/ (Markdown: https://insights.sbomify.com/CVE-2026-126072/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-126072
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-126072
- OSV: https://osv.dev/vulnerability/CVE-2026-126072

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-126072/
Summaries are generated and may contain mistakes; the official description above is the record.