CVE-2008-0891 in OpenSSL
Summary
by MITRE
Double free vulnerability in OpenSSL 0.9.8f and 0.9.8g, when the TLS server name extensions are enabled, allows remote attackers to cause a denial of service (crash) via a malformed Client Hello packet. NOTE: some of these details are obtained from third party information.
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Analysis
by VulDB Data Team • 11/28/2024
The vulnerability identified as CVE-2008-0891 represents a critical double free condition within the OpenSSL cryptographic library version 0.9.8f and 0.9.8g. This flaw specifically manifests when the TLS server name indication extension is enabled, creating a scenario where remote attackers can exploit malformed Client Hello packets to trigger a denial of service condition. The vulnerability stems from improper memory management within the SSL/TLS handshake process, particularly when processing server name extension data. When a malicious client sends a specially crafted Client Hello message containing malformed server name extensions, the OpenSSL implementation fails to properly handle the memory allocation and deallocation sequences, leading to the same memory block being freed twice. This double free condition corrupts the heap memory structure and ultimately results in a crash of the affected OpenSSL service.
The technical execution of this vulnerability follows a well-defined pattern that aligns with common memory corruption attack vectors. The OpenSSL library processes the server name extension data during the TLS handshake phase, where it allocates memory for storing server name information. When malformed data is received, the processing logic does not adequately validate the input structure, causing the library to attempt to free the same memory location multiple times. This memory corruption directly impacts the heap management system, leading to unpredictable behavior including program termination. The vulnerability is classified under CWE-415 as Double Free, which represents a common class of memory management errors that can lead to denial of service conditions. The attack vector requires only a network connection to the vulnerable service, making it particularly dangerous as it can be exploited by any remote attacker without authentication requirements.
The operational impact of this vulnerability extends beyond simple service disruption to encompass broader security implications for systems relying on OpenSSL for secure communications. When exploited successfully, the vulnerability causes immediate service unavailability, effectively performing a denial of service attack against the targeted system. This affects web servers, mail servers, and any application that utilizes OpenSSL for TLS/SSL connections. The vulnerability affects the core TLS handshake functionality, meaning that legitimate clients may be unable to establish secure connections to affected services until the underlying OpenSSL library is patched or updated. Organizations running vulnerable versions of OpenSSL face significant operational risk as attackers can easily exploit this condition to disrupt critical services without requiring elevated privileges or complex attack infrastructure. The vulnerability also demonstrates the importance of proper input validation in cryptographic libraries, as the issue originates from insufficient validation of extension data rather than fundamental cryptographic flaws.
Mitigation strategies for CVE-2008-0891 primarily focus on immediate patching and configuration adjustments to prevent exploitation. The most effective solution involves upgrading to OpenSSL version 0.9.8h or later, which contains the necessary memory management fixes to prevent the double free condition. System administrators should also consider implementing network-level protections such as firewalls or intrusion detection systems that can detect and block malformed Client Hello packets. Additionally, disabling the server name indication extension when not required can provide a temporary workaround, though this approach reduces functionality and should not be considered a permanent solution. The vulnerability highlights the importance of regular security updates and the need for robust input validation in cryptographic implementations. Organizations should also implement monitoring systems to detect unusual connection patterns or service disruptions that might indicate exploitation attempts. From an ATT&CK framework perspective, this vulnerability maps to T1499.004 (Unnecessary Service Stop) and T1566.001 (Phishing with Social Engineering) as attackers may use this vulnerability to disrupt services or as part of broader attack campaigns targeting secure communication channels. The vulnerability serves as a reminder of the critical importance of memory safety in cryptographic implementations and the potential for seemingly minor memory management flaws to result in significant service availability issues.