CVE-2020-5207 in Ktor
Summary
by MITRE
In Ktor before 1.3.0, request smuggling is possible when running behind a proxy that doesn't handle Content-Length and Transfer-Encoding properly or doesn't handle \n as a headers separator.
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Analysis
by VulDB Data Team • 03/27/2024
The vulnerability identified as CVE-2020-5207 affects the Ktor web framework version 1.3.0 and earlier, presenting a significant security risk through request smuggling attacks. This flaw emerges when Ktor applications operate behind reverse proxies that fail to properly process HTTP headers, particularly Content-Length and Transfer-Encoding parameters, or when proxies do not correctly handle header separation. The vulnerability stems from insufficient validation and processing of HTTP request headers within the framework's proxy handling mechanisms.
The technical implementation of this vulnerability exploits the inconsistent handling of HTTP header parsing between the Ktor application and upstream proxies. When a proxy server receives an HTTP request with conflicting or improperly formatted headers, it may interpret the same header information differently than the Ktor framework itself. This discrepancy creates opportunities for attackers to manipulate request boundaries and potentially inject malicious content or bypass security controls. The core issue manifests when the proxy fails to properly normalize or validate header values, allowing attackers to craft requests that appear legitimate to the proxy but are interpreted differently by the Ktor application.
The operational impact of CVE-2020-5207 extends beyond simple data interception, potentially enabling more sophisticated attacks including cache poisoning, cross-site scripting exploitation, and authentication bypass attempts. Attackers can leverage this vulnerability to manipulate how requests are processed and forwarded, creating scenarios where malicious payloads can be injected into the application layer or where legitimate requests are modified in transit. The vulnerability particularly affects applications deployed in environments where multiple proxy layers exist, such as load balancers, API gateways, or content delivery networks that may not properly normalize HTTP header values before forwarding requests to Ktor applications.
Security professionals should address this vulnerability through immediate framework upgrades to version 1.3.0 or later, which includes proper header validation and normalization mechanisms. Organizations should also implement comprehensive header processing validation at their proxy layers, ensuring that Content-Length and Transfer-Encoding headers are properly handled and normalized before reaching the Ktor application. The vulnerability aligns with CWE-16 Configuration and CWE-444 Inconsistent Interpretation of HTTP Requests, representing a classic case of HTTP request smuggling as documented in the MITRE ATT&CK framework under the technique of HTTP protocol manipulation. Network administrators should consider implementing additional monitoring and logging of HTTP header variations to detect potential exploitation attempts, while also reviewing proxy configurations to ensure proper header handling across the entire request processing chain.