CVE-2011-1473 in OpenSSL
Summary
by MITRE
** DISPUTED ** OpenSSL before 0.9.8l, and 0.9.8m through 1.x, does not properly restrict client-initiated renegotiation within the SSL and TLS protocols, which might make it easier for remote attackers to cause a denial of service (CPU consumption) by performing many renegotiations within a single connection, a different vulnerability than CVE-2011-5094. NOTE: it can also be argued that it is the responsibility of server deployments, not a security library, to prevent or limit renegotiation when it is inappropriate within a specific environment.
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Analysis
by VulDB Data Team • 08/07/2024
The vulnerability described in CVE-2011-1473 represents a significant weakness in the OpenSSL cryptographic library that affects versions prior to 0.9.8l and specifically excludes 0.9.8m through 1.x releases. This issue stems from inadequate restrictions on client-initiated renegotiation within the SSL and TLS protocols, creating a potential avenue for malicious actors to exploit the protocol's design flaws. The vulnerability operates at the protocol level where legitimate renegotiation requests can be abused to consume excessive computational resources, fundamentally undermining the system's availability through resource exhaustion attacks. The technical flaw manifests when clients can repeatedly initiate renegotiation sequences within a single established connection, leading to continuous CPU processing demands that can overwhelm server resources. This weakness directly relates to CWE-400, which categorizes improper resource management in software systems, specifically targeting the lack of proper resource limitation mechanisms in cryptographic protocol implementations.
The operational impact of this vulnerability extends beyond simple denial of service scenarios to encompass broader security implications for systems relying on SSL/TLS connections. Attackers can exploit this weakness by establishing a legitimate connection and then repeatedly initiating renegotiation requests, causing the server to consume disproportionate CPU cycles for processing these repeated handshake sequences. The vulnerability creates a scenario where a single client connection can effectively consume server resources at an unsustainable rate, potentially leading to complete system unavailability. This type of attack falls under the ATT&CK technique T1499.004, which describes resource exhaustion attacks targeting availability. The vulnerability's impact is particularly severe because it operates at the transport layer protocol level, making it difficult to detect and mitigate through traditional application-level security measures, as the requests appear legitimate within the established connection context.
The broader implications of this vulnerability highlight the critical importance of proper protocol implementation and resource management in cryptographic libraries. While some argue that server deployments should bear primary responsibility for limiting renegotiation in inappropriate environments, the vulnerability demonstrates that fundamental protocol weaknesses in security libraries create systemic risks that affect entire ecosystems. The issue also touches upon CWE-307, which addresses improper restriction of excessive authentication attempts, as the vulnerability allows for repeated authentication-like operations without proper rate limiting or resource constraints. Organizations deploying systems using affected OpenSSL versions must implement comprehensive monitoring and rate-limiting mechanisms to detect and prevent excessive renegotiation activities. The recommended mitigations include upgrading to OpenSSL versions that properly address the renegotiation restrictions, implementing connection-level rate limiting, and configuring servers to either disable renegotiation entirely or enforce strict limits on renegotiation frequency. Additionally, network-level firewalls and intrusion detection systems should be configured to monitor for unusual patterns of renegotiation activity that may indicate exploitation attempts.