CVE-2011-4108 in OpenSSL
Summary
by MITRE
The DTLS implementation in OpenSSL before 0.9.8s and 1.x before 1.0.0f performs a MAC check only if certain padding is valid, which makes it easier for remote attackers to recover plaintext via a padding oracle attack.
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Analysis
by VulDB Data Team • 08/07/2024
The vulnerability identified as CVE-2011-4108 represents a critical weakness in the Datagram Transport Layer Security implementation within OpenSSL cryptographic libraries. This flaw exists in versions prior to 0.9.8s and 1.0.0f, affecting both the legacy 0.9.8 series and the newer 1.0.0 series of the OpenSSL toolkit. The issue stems from an improper handling of message authentication codes within the DTLS protocol, creating a significant security gap that adversaries can exploit to compromise encrypted communications.
The technical root cause of this vulnerability lies in the implementation's failure to perform consistent MAC validation across all padding scenarios. Specifically, the DTLS implementation only executes message authentication code checks when certain padding conditions are met, rather than conducting validation regardless of padding structure. This selective validation creates a padding oracle condition where attackers can observe whether padding validation succeeds or fails, enabling them to perform iterative attacks that gradually reveal the plaintext content of encrypted messages. The vulnerability directly maps to CWE-209, which describes "Information Exposure Through an Error Message," and CWE-310, covering "Cryptographic Issues" in the context of improper implementation of cryptographic protocols.
The operational impact of this vulnerability is substantial as it allows remote attackers to conduct padding oracle attacks against DTLS connections without requiring privileged access or complex exploitation techniques. An attacker positioned to intercept network traffic can systematically manipulate packet padding and observe the server's responses to determine valid padding structures. This process enables the gradual recovery of plaintext data from encrypted DTLS communications, potentially exposing sensitive information such as session tokens, credentials, or application data. The vulnerability particularly affects applications using DTLS for secure communication over unreliable networks, including VoIP systems, IoT devices, and any service requiring secure datagram transmission.
Mitigation strategies for CVE-2011-4108 involve immediate upgrading of OpenSSL installations to versions 0.9.8s or 1.0.0f and later, which contain the necessary fixes to ensure consistent MAC validation regardless of padding conditions. Organizations should also implement network monitoring to detect unusual traffic patterns that might indicate exploitation attempts, while maintaining comprehensive logging of cryptographic operations for forensic analysis. Security teams should conduct thorough inventory assessments to identify all systems utilizing vulnerable OpenSSL versions and prioritize patching efforts based on risk exposure. The ATT&CK framework categorizes this vulnerability under T1595 for "Active Scanning" and T1071 for "Application Layer Protocol" as attackers may use this weakness to perform reconnaissance and establish persistent access through compromised encrypted communications. Additionally, implementing proper intrusion detection systems and network segmentation can help reduce the attack surface and limit potential lateral movement if exploitation occurs.