# CVE-2026-66754: tomaka rouille reachable assertion in Request::remove_prefix

Source: https://junglewise.ai/threats/cve-2026-66754-tomaka-rouille-reachable-assertion-in-request-remove-prefix  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-07-28. Updated: 2026-07-28  
License: CC BY 4.0 with a link back

CVE-2026-66754 · Severity: high · CVSS 7.5 · Published 2026-07-28

Rouille, a web server library for the Rust programming language, contains a flaw in how it handles specific web addresses. An unauthenticated attacker can send a specially crafted web request that causes the server to crash or return error messages. Depending on how the server is configured, this could lead to a complete service outage, impacting business operations and availability.

Technologies: [Tomaka Rouille](https://junglewise.ai/threats/technologies/rouille). Vendors: [Tomaka](https://junglewise.ai/threats/vendors/tomaka).

## Quick answers

**Is CVE-2026-66754 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-66754 being exploited in the wild.

**How severe is CVE-2026-66754?** High severity, with a CVSS score of 7.5, published 28 July 2026.

**Which products and versions are affected?** Tomaka Rouille 0.1.6 through 3.6.2.

**Is there a fix for CVE-2026-66754?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-66754 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-66754?** Check whether you run Tomaka Rouille at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

A reachable assertion vulnerability (CWE-617) exists in the `Request::remove_prefix` function of the Rouille library. The function performs a check on the percent-decoded URL path but executes an `assert!` statement against the raw, encoded path. By sending a request where the decoded path matches a configured prefix but the raw path does not (e.g., by percent-encoding a character within the prefix), an attacker can trigger an assertion failure. Depending on the Rust panic configuration, this results in either a 500 Internal Server Error or immediate process termination (Denial of Service). This attack is reachable over the network without authentication.

## Affected products

- tomaka rouille 0.1.6 through 3.6.2

## Timeline

- 2026-07-28: advisory: NVD and VulnCheck published the advisory.

## References

- [https://github.com/theopaid/Remote-Denial-of-Service-via-Reachable-Assertion-in-URL-Prefix-Handling-rouille-](https://github.com/theopaid/Remote-Denial-of-Service-via-Reachable-Assertion-in-URL-Prefix-Handling-rouille-)
- [https://www.vulncheck.com/advisories/rouille-reachable-assertion-dos-via-remove-prefix-percent-encoding](https://www.vulncheck.com/advisories/rouille-reachable-assertion-dos-via-remove-prefix-percent-encoding)

## Related threats

- [tomaka rouille HTTP request smuggling via header injection](https://junglewise.ai/threats/cve-2026-67182-tomaka-rouille-http-request-smuggling-via-header-injection)
- [Rouille HTTP request smuggling in proxy implementation](https://junglewise.ai/threats/cve-2026-67181-rouille-http-request-smuggling-in-proxy-implementation)
- [Rouille HTTP response splitting in response headers](https://junglewise.ai/threats/cve-2026-66746-rouille-http-response-splitting-in-response-headers)