CVE-2026-67182 in rouille
Summary
by MITRE • 07/28/2026
Rouille 0.3.3 through 3.6.2 contains an HTTP request smuggling vulnerability that allows remote attackers to bypass access controls by injecting bare line feed characters (0x0A) into client-supplied request header values that are copied verbatim to upstream connections without validation. Attackers can craft a header value containing a complete additional HTTP request that is interpreted as a separate request by backends such as Go net/http and Python http.server, causing the backend to process a smuggled request with attacker-chosen method, path, and headers that bypasses the rouille handler's access control logic.
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Analysis
by VulDB Data Team • 07/28/2026
The vulnerability in Rouille versions 0.3.3 through 3.6.2 represents a critical HTTP request smuggling flaw that exploits improper input validation in HTTP header processing. This issue stems from the application's failure to sanitize client-supplied header values before forwarding them to upstream servers, creating an avenue for attackers to inject bare line feed characters (0x0A) that manipulate the HTTP parsing behavior of backend components. The vulnerability manifests when Rouille copies header values verbatim to upstream connections without performing any validation or sanitization, allowing maliciously crafted headers to contain embedded HTTP requests that are interpreted as separate transactions by backend HTTP servers.
The technical implementation of this vulnerability leverages the fundamental differences in how various HTTP parsers handle input streams. When a client sends a header containing a bare line feed character followed by another HTTP request structure, backend servers like Go's net/http and Python's http.server interpret this as a legitimate second request rather than part of the original header value. This parsing inconsistency enables attackers to smuggle requests that bypass the application's access control mechanisms entirely, as the smuggled request operates independently of the main handler logic. The injected payload can contain arbitrary HTTP methods, paths, and headers that are processed by the backend server without any interference from Rouille's security controls.
This vulnerability has significant operational impact on systems using affected versions of Rouille, as it allows remote attackers to execute unauthorized actions through the application's backends. The smuggled requests can potentially access protected resources, perform administrative functions, or extract sensitive data that would normally be restricted by access control policies. The attack vector is particularly dangerous because it operates at the HTTP protocol level, making it difficult to detect through traditional application-level security measures and potentially bypassing network-based firewalls and intrusion detection systems that do not inspect HTTP content.
The vulnerability aligns with CWE-16 Configuration and CWE-444 Inconsistent Interpretation of HTTP Requests, representing a classic case of improper input validation in web applications. From an ATT&CK perspective, this maps to T1190 Proxy Trojan, T1571 Multi-hop Communication, and T1071.004 Application Layer Protocol: DNS, as attackers can leverage the smuggling technique to route traffic through intermediate systems while maintaining access to backend resources. Organizations should immediately update to versions of Rouille that address this vulnerability by implementing proper header sanitization and input validation before forwarding requests to upstream servers, ensuring that all client-supplied data is properly escaped or encoded to prevent interpretation as additional HTTP commands.