CVE-2020-36202 in async-h1 Crate
Summary
by MITRE • 01/26/2021
An issue was discovered in the async-h1 crate before 2.3.0 for Rust. Request smuggling can occur when used behind a reverse proxy.
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Analysis
by VulDB Data Team • 02/19/2021
The vulnerability identified as CVE-2020-36202 affects the async-h1 crate version 2.2.0 and earlier in the rust programming language ecosystem. This issue represents a significant security flaw that manifests when the crate is deployed behind reverse proxy configurations, creating opportunities for request smuggling attacks that can compromise the integrity of web applications. The async-h1 crate serves as an asynchronous http client and server implementation that processes http requests and responses in rust applications, making it a critical component in many web service architectures.
The technical flaw within async-h1 stems from improper handling of http request parsing and forwarding mechanisms when operating in reverse proxy scenarios. Specifically, the crate fails to properly normalize or validate http headers and request structures before forwarding requests to backend servers. This vulnerability allows malicious actors to manipulate http request boundaries and headers in ways that can cause the reverse proxy to incorrectly route or process requests. The issue is particularly dangerous because it leverages the trust relationship between the reverse proxy and backend services, enabling attackers to craft requests that appear legitimate to the proxy but contain malicious content or instructions that confuse the backend processing.
When exploited, this vulnerability can result in various operational impacts including unauthorized data access, request forgery, and potential service disruption. Attackers can manipulate how requests are forwarded through the reverse proxy, potentially bypassing security controls, accessing restricted resources, or causing the backend services to process malformed requests that could lead to crashes or unexpected behavior. The vulnerability essentially creates a communication channel where the reverse proxy and backend server interpret the same http request differently, opening pathways for malicious activity that can be difficult to detect and trace through conventional monitoring systems.
The security implications of this vulnerability align with common attack patterns documented in the attack technique framework, particularly those related to http request smuggling and protocol manipulation. This type of vulnerability is categorized under CWE-444 as improper handling of http requests, which directly relates to the core issue of incorrect request processing in reverse proxy environments. Organizations using the async-h1 crate in production environments are advised to upgrade to version 2.3.0 or later where the vulnerability has been addressed through improved http header validation and request normalization mechanisms. Additionally, implementing proper input validation at multiple layers of the application architecture, including reverse proxy configurations and backend service processing, can provide additional defense in depth measures against exploitation attempts.