CVE-2017-3733 in VM VirtualBox
Summary
by MITRE
During a renegotiation handshake if the Encrypt-Then-Mac extension is negotiated where it was not in the original handshake (or vice-versa) then this can cause OpenSSL 1.1.0 before 1.1.0e to crash (dependent on ciphersuite). Both clients and servers are affected.
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Analysis
by VulDB Data Team • 08/29/2024
The vulnerability described in CVE-2017-3733 represents a critical denial of service issue within OpenSSL's implementation of the Transport Layer Security protocol. This flaw manifests during TLS renegotiation handshakes when there is a mismatch in the Encrypt-Then-Mac extension negotiation between the original connection and the subsequent renegotiation. The Encrypt-Then-Mac extension is a security mechanism designed to prevent certain types of cryptographic attacks by ensuring that the MAC (Message Authentication Code) is computed after encryption rather than before. When this extension is present in the renegotiation but absent from the initial handshake, or vice versa, the OpenSSL implementation fails to handle this inconsistency gracefully. This specific vulnerability affects OpenSSL version 1.1.0 and earlier versions before 1.1.0e, making it particularly concerning as it represents a fundamental flaw in the TLS protocol implementation that could be exploited by attackers to disrupt secure communications. The vulnerability impacts both client and server implementations, meaning that any system using OpenSSL for TLS connections could be susceptible to this crash condition.
The technical root cause of this vulnerability stems from inadequate error handling within OpenSSL's TLS renegotiation logic. When the Encrypt-Then-Mac extension status differs between the original handshake and the renegotiation phase, the software fails to properly validate the extension state and subsequently attempts to process the connection in a manner that leads to memory corruption or invalid state transitions. This typically results in a segmentation fault or similar crash condition that terminates the TLS connection process. The crash behavior is dependent on the specific ciphersuite being used, which means that not all TLS configurations are equally vulnerable, but the potential for exploitation remains significant across the affected version range. This type of vulnerability falls under CWE-248, which addresses the issue of "Uncaught Exception" in software implementations, as the OpenSSL code fails to properly anticipate and handle the edge case of inconsistent extension negotiation during renegotiation.
The operational impact of CVE-2017-3733 extends beyond simple service disruption to potentially compromise the integrity of secure communication channels. An attacker who can initiate a TLS renegotiation with inconsistent Encrypt-Then-Mac extension states could force a target system to crash, effectively creating a denial of service condition that prevents legitimate users from establishing secure connections. This vulnerability is particularly dangerous in high-availability environments where maintaining continuous secure communication is critical, as it could be exploited to repeatedly disrupt services. The attack vector is relatively straightforward, requiring only the ability to establish a TLS connection and initiate a renegotiation with manipulated extension parameters. This vulnerability aligns with ATT&CK technique T1499.004, which covers "Endpoint Denial of Service" through service interruption. Organizations using affected OpenSSL versions face significant risk as this flaw could be exploited in both active attacks and passive reconnaissance activities that aim to identify vulnerable systems within their network infrastructure. The vulnerability demonstrates the critical importance of proper state management and error handling in cryptographic implementations, as even seemingly minor inconsistencies in protocol negotiation can lead to complete system failures.
Mitigation strategies for CVE-2017-3733 primarily involve upgrading to OpenSSL version 1.1.0e or later, where the vulnerability has been addressed through improved error handling and validation of TLS extension states during renegotiation. Organizations should also implement monitoring solutions to detect unusual TLS renegotiation patterns that might indicate exploitation attempts. Network administrators should consider disabling TLS renegotiation entirely where possible, as this removes the attack surface entirely. Additionally, implementing proper intrusion detection systems that can identify the specific patterns associated with this vulnerability can help in early detection of exploitation attempts. The fix implemented in OpenSSL 1.1.0e specifically addresses the inconsistent handling of the Encrypt-Then-Mac extension during renegotiation by ensuring that the protocol state is properly validated and maintained throughout the connection lifecycle. System administrators should also conduct thorough testing of their applications after applying the update to ensure compatibility with the patched OpenSSL implementation. This vulnerability highlights the need for comprehensive testing of edge cases in cryptographic implementations and demonstrates how protocol inconsistencies can lead to critical security failures. The remediation process should include not only updating the OpenSSL library but also verifying that all applications and services that depend on it are functioning correctly with the new version.