# CVE-2026-66754: Rouille 0.1.6 - 3.6.2 Reachable Assertion DoS via remove_prefix percent-encoding

> Remote attackers can crash the server by sending crafted percent-encoded URLs that trigger a reachable assertion failure in the Rouille library.

- **Severity:** High 8.2 (`CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 28 Jul 2026
- **Updated:** 29 Jul 2026
- **Also known as:** DEBIAN-CVE-2026-66754, GHSA-mrg5-7f6c-r28q

## What is CVE-2026-66754?

CVE-2026-66754 is a high-severity denial of service vulnerability in tomaka rouille, published on 28 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Rouille 0.1.6 through 3.6.2 contains a reachable assertion vulnerability in the Request::remove_prefix function that allows remote unauthenticated attackers to crash the server by sending a crafted percent-encoded URL. Attackers can send a request whose decoded path matches a configured prefix while the raw percent-encoded path does not, causing the assert! to fail and triggering either a 500 error or full process termination depending on the panic configuration.

Weakness: CWE-617 (Reachable Assertion)

## Which versions are affected by CVE-2026-66754?


## How do I fix CVE-2026-66754?

Upgrade to a fixed version.

## Is CVE-2026-66754 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-66754 exists.

Public exploit code:

- Security Advisory: Remote Denial of Service via Reachable Assertion in URL Prefix Handling (rouille) (github_poc): https://github.com/theopaid/CVE-2026-66754-Remote-Denial-of-Service-via-Reachable-Assertion-in-URL-Prefix-Handling-rouille-

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-66754 and fix it if it is affected.

What it is: CVE-2026-66754 is a high-severity denial of service vulnerability in tomaka rouille, published on 28 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-66754 exists.

Affected product: tomaka rouille. 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-2026-66754/ (Markdown: https://insights.sbomify.com/CVE-2026-66754/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-66754
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-66754
- OSV: https://osv.dev/vulnerability/CVE-2026-66754

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-66754/
Summaries are generated and may contain mistakes; the official description above is the record.