CVE-2020-11077 in Puma Gem
Summary
by MITRE
In Puma (RubyGem) before 4.3.5 and 3.12.6, a client could smuggle a request through a proxy, causing the proxy to send a response back to another unknown client. If the proxy uses persistent connections and the client adds another request in via HTTP pipelining, the proxy may mistake it as the first request's body. Puma, however, would see it as two requests, and when processing the second request, send back a response that the proxy does not expect. If the proxy has reused the persistent connection to Puma to send another request for a different client, the second response from the first client will be sent to the second client. This is a similar but different vulnerability from CVE-2020-11076. The problem has been fixed in Puma 3.12.6 and Puma 4.3.5.
If you want to get best quality of vulnerability data, you may have to visit VulDB.
Analysis
by VulDB Data Team • 10/19/2020
The vulnerability identified as CVE-2020-11077 represents a sophisticated HTTP request smuggling issue within the Puma web server implementation, specifically affecting Ruby applications that rely on this popular web server gem. This flaw exploits the interaction between Puma's request processing and proxy server behavior, creating a scenario where request boundaries become ambiguous and potentially lead to cross-client response leakage. The vulnerability manifests when a proxy server maintains persistent connections with Puma and handles HTTP pipelining, where multiple requests are sent over the same connection without waiting for responses. The issue stems from Puma's handling of request parsing where it treats pipelined requests differently than the proxy expects, creating a mismatch in connection state management and request routing.
The technical root cause of this vulnerability lies in the improper handling of HTTP request boundaries when persistent connections and pipelining are involved. When a client sends multiple requests through a proxy server using HTTP pipelining, the proxy server may mistakenly treat the second request as part of the first request's body due to connection reuse patterns. Puma's request parsing logic, however, recognizes these as distinct requests, leading to a scenario where the response to the second request gets delivered to the wrong client. This occurs because the proxy maintains connection state that doesn't align with Puma's internal request processing, creating a mismatch that allows response hijacking. The vulnerability is classified under CWE-444 as an Inconsistent Interpretation of HTTP Requests, specifically involving HTTP request smuggling techniques that exploit differences in how proxies and servers interpret pipelined requests.
The operational impact of CVE-2020-11077 extends beyond simple data leakage, potentially enabling attackers to access sensitive information belonging to other users or even execute unauthorized operations through response hijacking. When a proxy server reuses a persistent connection for different clients, the misaligned request processing can result in responses being delivered to incorrect recipients, effectively creating a cross-client information disclosure vulnerability. This type of vulnerability is particularly dangerous in environments where multiple users share proxy servers, as it can lead to session hijacking, credential exposure, or access to restricted resources. The vulnerability operates at the application layer and can be exploited without requiring authentication, making it particularly concerning for web applications that rely on proxy infrastructure for load balancing or security filtering. This issue represents a significant concern for organizations using Puma as their web server in production environments with proxy configurations.
Mitigation strategies for CVE-2020-11077 focus primarily on upgrading to patched versions of Puma, specifically versions 3.12.6 or 4.3.5, which contain fixes addressing the request boundary handling and connection state management issues. Organizations should implement comprehensive patch management procedures to ensure all instances of Puma are updated promptly. Additional mitigations include configuring proxy servers to disable HTTP pipelining when communicating with Puma servers, implementing proper connection handling policies, and monitoring for unusual request patterns that might indicate exploitation attempts. The fix addresses the underlying architectural issue by ensuring consistent request parsing behavior between Puma's internal processing and how proxy servers expect to handle persistent connections. Security teams should also consider implementing network segmentation and monitoring to detect potential exploitation attempts, as the vulnerability can be leveraged for information disclosure attacks. This vulnerability aligns with ATT&CK technique T1071.004 for application layer protocol manipulation and demonstrates the importance of proper HTTP request handling in web server implementations.