CVE-2002-0082 in mod_ssl
Summary
by MITRE
The dbm and shm session cache code in mod_ssl before 2.8.7-1.3.23, and Apache-SSL before 1.3.22+1.46, does not properly initialize memory using the i2d_SSL_SESSION function, which allows remote attackers to use a buffer overflow to execute arbitrary code via a large client certificate that is signed by a trusted Certificate Authority (CA), which produces a large serialized session.
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Analysis
by VulDB Data Team • 09/23/2025
The vulnerability described in CVE-2002-0082 represents a critical buffer overflow flaw within the mod_ssl module of Apache web servers. This issue specifically affects the session cache implementation that handles both dbm and shm (shared memory) storage mechanisms. The flaw exists in Apache versions prior to 2.8.7-1.3.23 and Apache-SSL versions prior to 1.3.22+1.46, making it a significant concern for organizations running these older server configurations. The vulnerability stems from improper memory initialization during the serialization process of SSL sessions, which occurs when client certificates are processed and stored in the session cache.
The technical root cause of this vulnerability lies in the i2d_SSL_SESSION function, which is responsible for serializing SSL session data into a binary format for storage. When a client presents a large certificate signed by a trusted Certificate Authority, the serialization process fails to properly initialize memory buffers before writing the serialized session data. This memory initialization failure creates a situation where the buffer allocated for storing the serialized session can be exceeded, leading to a classic buffer overflow condition. The overflow occurs because the code does not account for the potential size variations in client certificates, particularly those that are unusually large due to extended certificate attributes or multiple extensions.
The operational impact of this vulnerability is severe as it allows remote attackers to execute arbitrary code on the target system with the privileges of the Apache process. Attackers can exploit this by presenting a specially crafted client certificate that, when processed by the vulnerable mod_ssl module, triggers the buffer overflow condition. This attack vector is particularly dangerous because it requires only a valid certificate from a trusted CA, meaning that legitimate clients with valid certificates could potentially be used to deliver the exploit. The vulnerability essentially transforms a legitimate SSL session establishment process into a code execution vector, making it difficult to detect and prevent through traditional network monitoring approaches.
The attack scenario typically involves an attacker who has access to a certificate from a trusted CA, or who can obtain such a certificate through social engineering or other means. When the target Apache server processes this certificate through the vulnerable mod_ssl module, the session cache code attempts to serialize the certificate data and store it in memory. Due to the improper memory initialization, the serialized data overflows the allocated buffer, potentially allowing the attacker to overwrite adjacent memory locations and inject malicious code. This vulnerability aligns with CWE-121, which describes heap-based buffer overflow conditions, and represents a classic example of how improper memory management can lead to remote code execution. The exploitability of this vulnerability is enhanced by the fact that it does not require authentication or special privileges beyond what is normally required for SSL client authentication.
Organizations affected by this vulnerability should immediately implement mitigations including upgrading to Apache versions 2.8.7-1.3.23 or later, or Apache-SSL versions 1.3.22+1.46 or later, which contain the necessary patches to properly initialize memory during the serialization process. Additionally, administrators should consider implementing certificate size limits or validation rules that prevent extremely large certificates from being processed through the session cache. The ATT&CK framework categorizes this vulnerability under T1059.007, which covers command and scripting interpreter execution, as the successful exploitation would allow attackers to execute arbitrary commands on the affected system. Network administrators should also monitor for unusual certificate processing patterns and consider implementing intrusion detection systems that can identify potential exploitation attempts through anomalous SSL session establishment behavior.