CVE-2007-5135 in OpenSSL
Summary
by MITRE
Off-by-one error in the SSL_get_shared_ciphers function in OpenSSL 0.9.7 up to 0.9.7l, and 0.9.8 up to 0.9.8f, might allow remote attackers to execute arbitrary code via a crafted packet that triggers a one-byte buffer underflow. NOTE: this issue was introduced as a result of a fix for CVE-2006-3738. As of 20071012, it is unknown whether code execution is possible.
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Analysis
by VulDB Data Team • 07/29/2021
The vulnerability identified as CVE-2007-5135 represents a critical buffer underflow condition within the OpenSSL cryptographic library that affects versions 0.9.7 through 0.9.7l and 0.9.8 through 0.9.8f. This flaw manifests in the SSL_get_shared_ciphers function, which is responsible for determining the cryptographic ciphers that can be shared between client and server during the SSL/TLS handshake process. The issue stems from an off-by-one error that occurs when processing cipher suite lists, creating a scenario where a single byte of memory is accessed beyond the allocated buffer boundaries. This type of vulnerability falls under the CWE-121 category of buffer underflow conditions, which are particularly dangerous because they can lead to memory corruption and potentially arbitrary code execution. The vulnerability was introduced as part of a fix for CVE-2006-3738, demonstrating how security patches can sometimes introduce new weaknesses that may be exploited by sophisticated attackers.
The technical implementation of this vulnerability involves the SSL_get_shared_ciphers function incorrectly calculating array indices when processing cipher suite data structures. When a malicious client sends a specially crafted SSL handshake packet containing an invalid cipher suite list, the function fails to properly validate the bounds of its internal buffer operations. This specific buffer underflow creates a condition where the program attempts to read or write data one byte beyond the allocated memory space, potentially corrupting adjacent memory locations. The memory corruption can overwrite critical program variables, return addresses, or function pointers, which may allow a remote attacker to manipulate the execution flow of the affected OpenSSL implementation. The vulnerability operates at the protocol level during SSL/TLS handshakes, making it particularly dangerous as it can be triggered without authentication or prior interaction with the target system.
The operational impact of CVE-2007-5135 extends beyond simple denial of service scenarios to potentially enable full system compromise through remote code execution. When exploited successfully, this vulnerability allows attackers to inject malicious code into the memory space of OpenSSL processes, potentially gaining complete control over web servers, email servers, or any other system utilizing vulnerable OpenSSL implementations. The attack vector requires only a single malicious packet to be sent during the SSL/TLS handshake process, making it particularly attractive to automated exploitation tools. Systems running vulnerable versions of OpenSSL are at risk regardless of their network configuration, as the vulnerability can be triggered by any SSL/TLS connection attempt, including legitimate traffic. The exploitability of this vulnerability aligns with ATT&CK technique T1059.007 for command and scripting interpreter, as successful exploitation could enable attackers to execute arbitrary commands on compromised systems, and T1566 for credential access through social engineering, as the vulnerability could be leveraged to establish persistent access.
Organizations affected by CVE-2007-5135 should immediately implement mitigations through comprehensive patch management procedures targeting the specific OpenSSL versions containing the vulnerability. The recommended approach involves upgrading to OpenSSL versions 0.9.7m, 0.9.8g, or later, which contain the corrected implementation of the SSL_get_shared_ciphers function. System administrators should conduct thorough inventory assessments to identify all systems running vulnerable OpenSSL versions, particularly web servers, mail servers, database servers, and any application that utilizes SSL/TLS encryption. Additionally, network monitoring should be enhanced to detect unusual SSL/TLS handshake patterns that might indicate exploitation attempts. The vulnerability's introduction as part of a previous fix also emphasizes the importance of thorough regression testing when implementing security patches, ensuring that remediation efforts do not inadvertently introduce new attack surfaces. Security teams should consider implementing intrusion detection systems with signature-based detection capabilities specifically designed to identify exploitation attempts targeting this vulnerability, as the memory corruption characteristics make it detectable through behavioral analysis of network traffic patterns.