CVE-2016-2109 in Mac OS X
Summary
by MITRE
The asn1_d2i_read_bio function in crypto/asn1/a_d2i_fp.c in the ASN.1 BIO implementation in OpenSSL before 1.0.1t and 1.0.2 before 1.0.2h allows remote attackers to cause a denial of service (memory consumption) via a short invalid encoding.
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Analysis
by VulDB Data Team • 09/06/2022
The vulnerability identified as CVE-2016-2109 represents a critical memory consumption issue within OpenSSL's ASN.1 BIO implementation that affects versions prior to 1.0.1t and 1.0.2h. This flaw exists in the asn1_d2i_read_bio function located in crypto/asn1/a_d2i_fp.c, which processes ASN.1 encoded data through BIO (Basic I/O) operations. The vulnerability stems from insufficient input validation during the parsing of ASN.1 encoded data structures, specifically when handling invalid or malformed encodings. Attackers can exploit this weakness by sending carefully crafted short invalid ASN.1 encodings to vulnerable systems, causing the OpenSSL library to consume excessive memory resources during the parsing process.
The technical nature of this vulnerability aligns with CWE-129, which describes improper validation of array indices, and CWE-400, which covers unspecified resource management issues. The flaw operates at the protocol level where ASN.1 decoding routines fail to properly handle malformed input, leading to unbounded memory allocation patterns. When the asn1_d2i_read_bio function encounters a short invalid encoding, it enters a processing loop that continuously allocates memory without proper bounds checking, eventually exhausting available system resources. This behavior constitutes a classic denial of service attack vector that can be executed remotely without authentication requirements, making it particularly dangerous in networked environments where OpenSSL is used for SSL/TLS operations.
The operational impact of CVE-2016-2109 extends beyond simple service disruption to potentially compromise entire systems through resource exhaustion attacks. Network services relying on OpenSSL for certificate processing, SSL/TLS connections, or any ASN.1 data handling become vulnerable to memory exhaustion attacks that can be triggered by sending malformed ASN.1 data to any endpoint using vulnerable OpenSSL versions. This vulnerability affects a wide range of applications including web servers, email servers, VPN services, and any system that utilizes OpenSSL for cryptographic operations. The attack can be executed through various vectors such as HTTPS connections, SMTP mail exchanges, or any protocol that employs SSL/TLS with vulnerable OpenSSL implementations, making it a significant threat to infrastructure security.
Mitigation strategies for CVE-2016-2109 primarily involve immediate patching of affected OpenSSL installations to versions 1.0.1t or 1.0.2h and later. System administrators should implement comprehensive monitoring for unusual memory consumption patterns that could indicate exploitation attempts. Network segmentation and rate limiting controls can help reduce the impact of potential attacks by limiting the number of connections or requests that can be processed within a given time frame. Additionally, implementing intrusion detection systems that can identify malformed ASN.1 traffic patterns provides an additional layer of defense. Organizations should also consider deploying application firewalls or web application firewalls that can filter out suspicious ASN.1 data before it reaches vulnerable OpenSSL components. The vulnerability demonstrates the importance of robust input validation and proper resource management in cryptographic libraries, as outlined in the ATT&CK framework's resource exhaustion tactics that emphasize the exploitation of memory management flaws to compromise system availability.