CVE-2021-38512 in actix-http Crate
Summary
by MITRE • 08/11/2021
An issue was discovered in the actix-http crate before 3.0.0-beta.9 for Rust. HTTP/1 request smuggling (aka HRS) can occur, potentially leading to credential disclosure.
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Analysis
by VulDB Data Team • 08/15/2021
The vulnerability identified as CVE-2021-38512 represents a critical HTTP/1 request smuggling flaw within the actix-http crate, a widely used asynchronous HTTP library for rust applications. This security issue affects versions prior to 3.0.0-beta.9 and exposes systems to sophisticated attack vectors that can compromise user credentials and sensitive data. The flaw stems from improper handling of HTTP request parsing and validation mechanisms within the crate's implementation, creating opportunities for malicious actors to manipulate HTTP message boundaries and inject unauthorized requests. The vulnerability specifically impacts the HTTP/1 protocol implementation where the crate fails to properly validate request boundaries and content length headers, allowing attackers to craft malformed requests that can be interpreted differently by upstream servers and proxies.
The technical exploitation of this vulnerability leverages HTTP/1 request smuggling techniques that manipulate how HTTP requests are parsed and processed. The flaw occurs when the actix-http crate does not adequately validate the Content-Length header or Transfer-Encoding headers during request processing, enabling attackers to craft requests where the server interprets different portions of a single HTTP message as separate requests. This creates a scenario where an attacker can inject additional requests that may bypass authentication mechanisms or access unauthorized resources. The vulnerability falls under CWE-444, which specifically addresses improper handling of HTTP requests, and aligns with ATT&CK technique T1190 for exploiting vulnerabilities in web applications. The implementation issue stems from the crate's insufficient state management during HTTP message parsing, particularly when handling chunked transfer encoding and content length validation.
The operational impact of CVE-2021-38512 extends beyond simple data exposure to encompass potential credential compromise and unauthorized access to protected resources. When exploited, this vulnerability can enable attackers to perform session hijacking, access user accounts without proper authentication, or even escalate privileges within applications that rely on the affected crate. The risk is particularly elevated in environments where the actix-http crate is used in reverse proxy configurations, load balancers, or web applications that process user requests through HTTP middleware. Organizations running applications built with affected versions of the crate face significant exposure to credential disclosure attacks, especially in scenarios involving shared infrastructure or when the application communicates with other services that may be vulnerable to request smuggling attacks. The vulnerability's impact is amplified in microservices architectures where HTTP request smuggling can be used to bypass security controls between service components.
Mitigation strategies for CVE-2021-38512 require immediate action to upgrade the affected actix-http crate to version 3.0.0-beta.9 or later, which includes proper validation of HTTP request headers and enhanced parsing mechanisms that prevent the exploitation of request smuggling vulnerabilities. Organizations should also implement comprehensive monitoring of HTTP request patterns and content length validation to detect potential exploitation attempts. Additional defensive measures include deploying web application firewalls that can identify and block suspicious HTTP request sequences, implementing strict header validation policies, and conducting thorough security reviews of all HTTP handling components within the application stack. The fix addresses the core parsing logic by ensuring proper handling of Content-Length and Transfer-Encoding headers, implementing stricter validation of HTTP message boundaries, and enhancing the overall state management during request processing to prevent the conditions that enable HTTP/1 request smuggling attacks.