CVE-2016-7053 in OpenSSL
Summary
by MITRE
In OpenSSL 1.1.0 before 1.1.0c, applications parsing invalid CMS structures can crash with a NULL pointer dereference. This is caused by a bug in the handling of the ASN.1 CHOICE type in OpenSSL 1.1.0 which can result in a NULL value being passed to the structure callback if an attempt is made to free certain invalid encodings. Only CHOICE structures using a callback which do not handle NULL value are affected.
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Analysis
by VulDB Data Team • 10/03/2022
The vulnerability identified as CVE-2016-7053 represents a critical null pointer dereference issue within OpenSSL version 1.1.0 prior to 1.1.0c, specifically affecting applications that process Cryptographic Message Syntax (CMS) structures. This flaw manifests when malformed CMS encodings are encountered during parsing operations, leading to application crashes through direct memory access violations. The vulnerability operates at the core of OpenSSL's ASN.1 parsing mechanisms, where the library's handling of CHOICE type elements fails to properly validate input data before invoking callback functions. This particular weakness falls under the CWE-476 category of NULL Pointer Dereference, which is a well-documented software security flaw that can be exploited to cause denial of service conditions.
The technical implementation of this vulnerability stems from OpenSSL 1.1.0's modified ASN.1 CHOICE handling logic, which introduced changes to how the library processes complex data structures containing multiple possible types. When an invalid CMS structure is parsed, the ASN.1 parser attempts to free memory associated with the malformed encoding but fails to properly check whether the structure callback function receives a NULL value. This occurs specifically within CHOICE structures that utilize callback mechanisms, where the callback function is designed to process different types of data but does not include proper NULL value validation. The flaw is particularly insidious because it only affects applications using specific callback patterns that fail to handle NULL inputs, making it difficult to detect during normal operation and potentially exploitable in environments where CMS processing is critical.
The operational impact of CVE-2016-7053 extends beyond simple application crashes to encompass broader system reliability concerns, particularly in environments where OpenSSL is used for secure communications, digital signatures, and certificate processing. Any application that processes CMS messages, such as email systems, secure messaging platforms, or certificate authority services, becomes vulnerable to denial of service attacks when encountering malformed CMS structures. The vulnerability aligns with ATT&CK technique T1499.004 for network denial of service, as it can be exploited to disrupt services by sending specially crafted CMS messages that cause application crashes. Organizations relying on OpenSSL for cryptographic operations face significant risk, as attackers could potentially craft malicious CMS encodings to repeatedly crash services, leading to service unavailability and potential business disruption.
Mitigation strategies for CVE-2016-7053 focus primarily on updating to OpenSSL version 1.1.0c or later, which contains the necessary patches to address the null pointer dereference issue. System administrators should implement comprehensive patch management procedures to ensure all OpenSSL installations are updated promptly, particularly in environments handling sensitive cryptographic operations. Additionally, applications should be reviewed to ensure proper input validation is implemented when processing CMS structures, with defensive programming techniques such as NULL checks before callback invocations. Network monitoring solutions should be configured to detect unusual patterns of application crashes or service disruptions that might indicate exploitation attempts. The vulnerability demonstrates the importance of thorough testing of ASN.1 parsing logic and proper error handling in cryptographic libraries, as the issue affects core infrastructure components that form the foundation of secure communications in countless applications and systems worldwide.