CVE-2008-1672 in OpenSSL
Summary
by MITRE
OpenSSL 0.9.8f and 0.9.8g allows remote attackers to cause a denial of service (crash) via a TLS handshake that omits the Server Key Exchange message and uses "particular cipher suites," which triggers a NULL pointer dereference.
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Analysis
by VulDB Data Team • 12/30/2024
The vulnerability identified as CVE-2008-1672 represents a critical denial of service flaw within OpenSSL versions 0.9.8f and 0.9.8g that specifically targets the Transport Layer Security handshake process. This vulnerability operates through a carefully crafted TLS handshake sequence that deliberately omits the Server Key Exchange message while employing specific cipher suites that trigger the software crash. The flaw exists in the cryptographic handshake implementation where the OpenSSL library fails to properly validate the absence of required handshake components, leading to a null pointer dereference condition that terminates the application process.
The technical root cause of this vulnerability stems from inadequate input validation within the TLS handshake processing logic. When a client connects using particular cipher suites such as those involving ephemeral Diffie-Hellman key exchange, the server-side OpenSSL implementation expects certain handshake messages to be present. However, when the Server Key Exchange message is omitted, the code path attempts to dereference a null pointer that should have been initialized or validated earlier in the handshake sequence. This condition falls under the CWE-476 category of NULL Pointer Dereference, where a program attempts to access memory through a null pointer reference without proper validation.
From an operational perspective, this vulnerability presents a significant risk to systems relying on OpenSSL for secure communications, particularly web servers, email servers, and any application that utilizes TLS encryption. Attackers can exploit this flaw by establishing a TLS connection with a specially crafted handshake that omits the Server Key Exchange message while using vulnerable cipher suites. The impact manifests as an immediate application crash or termination, effectively causing a denial of service that disrupts legitimate user access to services. This vulnerability is particularly dangerous because it can be exploited remotely without requiring authentication or specialized privileges, making it an attractive target for malicious actors seeking to disrupt services.
The vulnerability demonstrates characteristics consistent with the attack pattern described in the MITRE ATT&CK framework under the T1499 category of Network Denial of Service, where adversaries leverage weaknesses in network protocols to cause service disruption. The specific exploitation technique involves manipulating the TLS handshake sequence to trigger a program crash, which aligns with the broader category of software exploitation techniques that target memory corruption vulnerabilities. The fact that this affects multiple cipher suites indicates that the vulnerability is not limited to a single protocol variant but rather represents a fundamental flaw in how OpenSSL processes certain handshake configurations.
Organizations affected by this vulnerability should immediately implement mitigations including upgrading to OpenSSL version 0.9.8h or later, which contains the necessary patches to properly validate handshake sequences and prevent the null pointer dereference. System administrators should also consider implementing network-level protections such as connection rate limiting and monitoring for unusual TLS handshake patterns that might indicate attempted exploitation. Additionally, organizations should review their cipher suite configurations to avoid using vulnerable combinations and ensure that their OpenSSL implementations are regularly updated to address similar vulnerabilities. The patch for this vulnerability specifically addresses the validation logic in the TLS handshake processing code, ensuring that all required handshake components are properly checked before attempting to access related data structures.