CVE-2013-0166 in OpenSSL
Summary
by MITRE
OpenSSL before 0.9.8y, 1.0.0 before 1.0.0k, and 1.0.1 before 1.0.1d does not properly perform signature verification for OCSP responses, which allows remote OCSP servers to cause a denial of service (NULL pointer dereference and application crash) via an invalid key.
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Analysis
by VulDB Data Team • 12/26/2024
The vulnerability described in CVE-2013-0166 represents a critical flaw in OpenSSL's handling of Online Certificate Status Protocol responses that can be exploited to cause denial of service conditions. This issue affects multiple versions of the OpenSSL library including 0.9.8y and earlier, 1.0.0k and earlier, and 1.0.1d and earlier releases. The vulnerability stems from improper signature verification mechanisms within the OCSP response processing functionality, creating a scenario where malicious OCSP servers can manipulate responses to trigger application instability.
The technical flaw manifests when OpenSSL processes OCSP responses that contain invalid cryptographic signatures or malformed key structures. During signature verification operations, the library fails to properly validate the integrity of the signature data before attempting to process it, leading to a NULL pointer dereference condition. This occurs because the verification routine does not adequately check for valid key parameters or signature structures, allowing an attacker-controlled OCSP response to contain malformed data that causes the application to attempt to dereference a null pointer during the verification process. The vulnerability specifically impacts the cryptographic signature validation component of OCSP processing, which is a critical function for certificate status checking in secure communications.
The operational impact of this vulnerability extends beyond simple service disruption to potentially compromise the availability of security services that depend on OCSP validation. When exploited, the vulnerability can cause applications using OpenSSL to crash immediately, resulting in denial of service for legitimate users attempting to establish secure connections. This is particularly concerning in environments where OCSP stapling is enabled, as the vulnerability can affect web servers, email servers, and other applications that rely on certificate status verification. The crash occurs at the application level rather than at the system level, making it difficult to distinguish from other application failures and potentially allowing for covert exploitation patterns.
This vulnerability maps to CWE-476 which describes NULL pointer dereference conditions, and aligns with ATT&CK technique T1499.004 which covers network denial of service attacks. The attack surface is broad as any application using OpenSSL for certificate validation and OCSP response processing is potentially vulnerable. Organizations should implement immediate patching strategies to update to versions of OpenSSL that address this signature verification flaw. Additionally, network monitoring should be enhanced to detect unusual OCSP response patterns that might indicate exploitation attempts, and certificate validation should be configured to include additional integrity checks beyond basic signature verification. The vulnerability demonstrates the critical importance of proper cryptographic implementation and validation in security libraries, as flaws in signature verification can have cascading effects on system availability and security posture.