CVE-2015-3194 in Xcode
Summary
by MITRE
crypto/rsa/rsa_ameth.c in OpenSSL 1.0.1 before 1.0.1q and 1.0.2 before 1.0.2e allows remote attackers to cause a denial of service (NULL pointer dereference and application crash) via an RSA PSS ASN.1 signature that lacks a mask generation function parameter.
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Analysis
by VulDB Data Team • 09/28/2022
The vulnerability identified as CVE-2015-3194 represents a critical denial of service weakness within the OpenSSL cryptographic library affecting versions prior to 1.0.1q and 1.0.2e. This flaw resides in the rsa_ameth.c file which handles RSA algorithm method implementations, specifically impacting the processing of RSA PSS signatures. The vulnerability manifests when the application encounters an RSA PSS ASN.1 signature that is missing the mandatory mask generation function parameter, creating a scenario where the cryptographic library fails to properly validate the signature structure before attempting to process it.
The technical execution of this vulnerability involves a NULL pointer dereference condition that occurs during the parsing of RSA PSS signatures. When OpenSSL attempts to process an ASN.1 signature structure lacking the mask generation function parameter, the internal code path fails to properly handle the missing parameter, resulting in an attempt to dereference a NULL pointer. This fundamental error in memory management causes the application to crash immediately upon encountering such malformed signatures, effectively enabling remote attackers to perform denial of service attacks against systems utilizing vulnerable OpenSSL versions.
This vulnerability directly maps to CWE-476 which describes NULL pointer dereference conditions in software implementations. The operational impact extends beyond simple service disruption as it can be exploited by remote attackers without authentication, making it particularly dangerous in networked environments where OpenSSL is used for SSL/TLS certificate validation or signature processing. Systems that process RSA PSS signatures from untrusted sources become vulnerable to this attack, including web servers, email servers, and any application that relies on OpenSSL for cryptographic operations involving RSA signatures.
The attack vector requires minimal privileges and can be executed remotely against vulnerable systems, making it a significant concern for infrastructure security. The vulnerability affects systems that process RSA PSS signatures regardless of whether they are acting as servers or clients, as the flaw occurs during signature validation rather than during active cryptographic operations. Organizations running vulnerable versions of OpenSSL should prioritize immediate patching, as the vulnerability can be exploited through various means including SSL/TLS handshake processing, certificate validation, or any other mechanism that processes RSA PSS signatures.
Mitigation strategies should focus on updating to patched versions of OpenSSL, specifically 1.0.1q or 1.0.2e, which contain proper validation checks for the mask generation function parameter. Additionally, administrators should implement network monitoring to detect unusual signature processing patterns and consider implementing signature validation policies that reject malformed signatures at the network boundary. The vulnerability demonstrates the importance of proper input validation in cryptographic libraries and highlights the need for comprehensive testing of edge cases in signature processing algorithms. This flaw also relates to ATT&CK technique T1499 which covers network denial of service attacks and emphasizes the critical nature of maintaining secure cryptographic implementations in production environments.