# CVE-2026-67991: Denial of service in n/a

> An attacker can cause denial of service via excessive CPU consumption in the RubyLLM library by submitting crafted long names.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 13 Aug 2026
- **Updated:** 4 Sep 2026
- **Also known as:** GHSA-42r3-x6vx-x49x

## What is CVE-2026-67991?

CVE-2026-67991 is a high-severity denial of service vulnerability in n/a, published on 13 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

crmne/ruby_llm at commit fa6f279847d6d7027814539d9c0dfc3bbdfd2a83 contains a polynomial-time regular expression denial-of-service condition in RubyLLM::Utils.underscore on Ruby 3.1.x. A very long crafted class, agent, or tool name can cause excessive CPU consumption and a denial of service.

Weakness: CWE-1333 (Inefficient Regular Expression Complexity)

## Which versions are affected by CVE-2026-67991?


## How do I fix CVE-2026-67991?

No fix has been published for CVE-2026-67991 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-67991 being exploited?

There is no known exploitation of CVE-2026-67991 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-67991 and fix it if it is affected.

What it is: CVE-2026-67991 is a high-severity denial of service vulnerability in n/a, published on 13 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-67991 in the wild and no public exploit code.

Affected product: n/a. No package-level version data is available, so check the vendor advisory linked from the reference page.

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-2026-67991/ (Markdown: https://insights.sbomify.com/CVE-2026-67991/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-67991
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-67991
- OSV: https://osv.dev/vulnerability/CVE-2026-67991

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-67991/
Summaries are generated and may contain mistakes; the official description above is the record.