CVE-2015-0293 in OpenSSL
Summary
by MITRE
The SSLv2 implementation in OpenSSL before 0.9.8zf, 1.0.0 before 1.0.0r, 1.0.1 before 1.0.1m, and 1.0.2 before 1.0.2a allows remote attackers to cause a denial of service (s2_lib.c assertion failure and daemon exit) via a crafted CLIENT-MASTER-KEY message.
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Analysis
by VulDB Data Team • 04/15/2022
The vulnerability described in CVE-2015-0293 represents a critical denial of service flaw within OpenSSL's SSLv2 protocol implementation that affected multiple version branches of the cryptographic library. This vulnerability specifically targets the s2_lib.c file which handles SSLv2 client-side operations and demonstrates how improper input validation can lead to catastrophic system failures. The issue manifests when a remote attacker crafts a specially formatted CLIENT-MASTER-KEY message that triggers an assertion failure within the OpenSSL library, causing the affected daemon to terminate abruptly and potentially leaving the system unavailable to legitimate users.
The technical exploitation of this vulnerability occurs through the manipulation of SSLv2 protocol messages during the handshake process where the client sends a CLIENT-MASTER-KEY message to establish encrypted communication. When OpenSSL processes this malformed message, it encounters an assertion failure in the s2_lib.c source file that was designed to validate certain cryptographic parameters and session states. This assertion failure causes the program to exit immediately, effectively terminating the service and rendering the system inaccessible to both legitimate users and potential attackers attempting to establish secure connections. The vulnerability is particularly dangerous because it can be triggered without requiring authentication or specialized privileges, making it a significant concern for any system running vulnerable versions of OpenSSL.
From an operational perspective, this vulnerability poses severe risks to network infrastructure and services that rely on OpenSSL for secure communications. When exploited, the denial of service condition can result in complete service unavailability, potentially affecting web servers, email servers, and other network services that depend on SSL/TLS encryption. The impact extends beyond simple service disruption as it can compromise the availability of critical business applications and potentially provide attackers with opportunities to conduct further reconnaissance or launch additional attacks against the compromised systems. Organizations running vulnerable OpenSSL versions face significant operational risks including potential revenue loss, service degradation, and increased security exposure that can persist until the vulnerability is properly patched.
The vulnerability aligns with CWE-129, which addresses improper validation of input boundaries, and demonstrates how insufficient validation of protocol message parameters can lead to program termination. From an ATT&CK framework perspective, this vulnerability maps to the T1499.004 technique related to Network Denial of Service, where attackers can exploit weaknesses in network protocols to render systems unavailable. The remediation strategy involves immediate upgrading of OpenSSL installations to versions that contain the necessary patches, specifically versions 0.9.8zf, 1.0.0r, 1.0.1m, and 1.0.2a or later. Organizations should also consider disabling SSLv2 protocol support entirely, as this protocol version has known security weaknesses and is deprecated in modern security standards. Additionally, implementing proper network monitoring and intrusion detection systems can help identify exploitation attempts and provide early warning of potential attacks targeting this vulnerability.