CVE-2015-1792 in OpenSSL
Summary
by MITRE
The do_free_upto function in crypto/cms/cms_smime.c in OpenSSL before 0.9.8zg, 1.0.0 before 1.0.0s, 1.0.1 before 1.0.1n, and 1.0.2 before 1.0.2b allows remote attackers to cause a denial of service (infinite loop) via vectors that trigger a NULL value of a BIO data structure, as demonstrated by an unrecognized X.660 OID for a hash function.
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Analysis
by VulDB Data Team • 05/21/2022
The vulnerability identified as CVE-2015-1792 represents a critical denial of service flaw within the OpenSSL cryptographic library that affects multiple version branches including 0.9.8, 1.0.0, 1.0.1, and 1.0.2 series. This weakness resides in the do_free_upto function located within the crypto/cms/cms_smime.c file, which handles S/MIME message processing and cryptographic operations. The vulnerability manifests when the system encounters a malformed X.660 OID that references an unrecognized hash function, creating a scenario where the BIO data structure receives a NULL value that the function cannot properly handle. This specific condition leads to an infinite loop during the processing of CMS (Cryptographic Message Syntax) messages, effectively causing a denial of service condition that can bring systems to a complete halt.
The technical exploitation of this vulnerability requires an attacker to craft a specially formatted S/MIME message containing an unrecognized X.660 OID that references a hash function not supported by the OpenSSL implementation. When the OpenSSL library attempts to process this message, the do_free_upto function encounters a NULL value in the BIO data structure and enters an infinite loop while trying to free memory resources. The CWE-835 reference applies here as this represents an infinite loop condition that can be triggered through improper handling of NULL pointers during memory deallocation operations. This flaw specifically impacts the CMS message processing functionality within OpenSSL, which is commonly used for secure email communication and digital signatures in enterprise environments.
The operational impact of CVE-2015-1792 extends beyond simple service disruption as it can affect critical infrastructure components that rely on OpenSSL for secure communications. Systems running vulnerable versions of OpenSSL may experience complete denial of service, requiring manual intervention and system restarts to restore functionality. The vulnerability affects both client and server implementations of OpenSSL, meaning that any application or service using OpenSSL for S/MIME processing could be compromised. Organizations using email servers, secure web applications, or any system that processes CMS messages are at risk, with the potential for cascading failures in interconnected systems that depend on secure communication channels. The ATT&CK framework categorizes this as a denial of service attack vector under the T1499.004 technique for network denial of service, which can be executed through software exploitation of memory management functions.
Mitigation strategies for CVE-2015-1792 primarily focus on immediate version upgrades to patched OpenSSL releases that address the NULL pointer dereference issue in the do_free_upto function. Organizations should prioritize updating their OpenSSL installations to versions 0.9.8zg, 1.0.0s, 1.0.1n, or 1.0.2b and later, depending on their current version. Additionally, implementing network-level protections such as rate limiting and input validation for S/MIME message processing can help reduce the attack surface while patches are deployed. Security monitoring should include detection of unusual memory usage patterns or process hanging that may indicate exploitation attempts. System administrators should also consider implementing application-level sandboxing for CMS message processing and regular security audits to identify and remediate similar vulnerabilities in cryptographic libraries. The vulnerability serves as a reminder of the critical importance of maintaining up-to-date cryptographic libraries and proper input validation in security-sensitive applications.