CVE-2011-3210 in OpenSSL
Summary
by MITRE
The ephemeral ECDH ciphersuite functionality in OpenSSL 0.9.8 through 0.9.8r and 1.0.x before 1.0.0e does not ensure thread safety during processing of handshake messages from clients, which allows remote attackers to cause a denial of service (daemon crash) via out-of-order messages that violate the TLS protocol.
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Analysis
by VulDB Data Team • 08/06/2024
The vulnerability identified as CVE-2011-3210 represents a critical thread safety issue within OpenSSL's implementation of ephemeral elliptic curve Diffie-Hellman (ECDH) ciphersuites. This flaw affects OpenSSL versions 0.9.8 through 0.9.8r and 1.0.x before 1.0.0e, specifically targeting the handshake message processing mechanisms during TLS protocol negotiations. The vulnerability stems from inadequate synchronization controls within the cryptographic handshake implementation, creating a condition where concurrent access to shared resources during ECDH key exchange operations can result in unpredictable behavior. This issue manifests when the TLS server processes handshake messages that arrive out of their expected sequence, a scenario that should be handled gracefully according to TLS protocol specifications but instead triggers a daemon crash.
The technical exploitation of this vulnerability occurs through carefully crafted malicious handshake messages that violate the expected TLS protocol order. When a remote attacker sends such out-of-order messages during the ECDH key exchange phase, the lack of proper thread synchronization causes the OpenSSL daemon to enter an inconsistent state. The flaw resides in the cryptographic library's handling of concurrent connections where multiple threads attempt to process handshake messages simultaneously without adequate mutual exclusion mechanisms. This thread safety failure results in memory corruption or invalid state transitions that ultimately lead to the daemon crashing and becoming unavailable to legitimate users. The vulnerability specifically impacts the ephemeral ECDH ciphersuite functionality, which is used for forward secrecy in TLS connections, making it particularly concerning for secure communications.
The operational impact of this vulnerability extends beyond simple service disruption, as it enables remote attackers to perform denial of service attacks against TLS servers that utilize OpenSSL with ECDH ciphersuites. Organizations running affected OpenSSL versions may experience complete service unavailability, requiring manual intervention to restart affected services and potentially causing cascading failures in systems relying on these secure communication channels. The vulnerability is particularly dangerous because it can be exploited without authentication, allowing any remote attacker to disrupt services simply by connecting to the vulnerable server and sending malformed handshake messages. This makes it a significant threat to web servers, email servers, and any other services that rely on OpenSSL for secure TLS connections, especially in environments where service availability is critical.
Mitigation strategies for CVE-2011-3210 primarily focus on upgrading to patched versions of OpenSSL where the thread safety issues have been resolved. Organizations should immediately update to OpenSSL 1.0.0e or later for the 1.0.x branch, or to the latest stable 0.9.8 version that includes the necessary fixes. System administrators should also consider disabling ephemeral ECDH ciphersuites if they are not essential for their security requirements, as this provides an additional layer of protection while the upgrade process is underway. Network monitoring should be enhanced to detect unusual connection patterns that might indicate exploitation attempts, and intrusion detection systems should be configured to alert on malformed TLS handshake sequences. The vulnerability aligns with CWE-362, which describes concurrent execution using shared resource vulnerabilities, and maps to ATT&CK technique T1499.004 for network denial of service attacks. Security teams should also implement proper patch management procedures to ensure rapid deployment of security updates across all affected systems, as this vulnerability was widely exploited in the wild during its active period.