CVE-2016-2108 in Mac OS X
Summary
by MITRE
The ASN.1 implementation in OpenSSL before 1.0.1o and 1.0.2 before 1.0.2c allows remote attackers to execute arbitrary code or cause a denial of service (buffer underflow and memory corruption) via an ANY field in crafted serialized data, aka the "negative zero" issue.
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Analysis
by VulDB Data Team • 09/06/2022
The vulnerability identified as CVE-2016-2108 represents a critical buffer underflow and memory corruption flaw within OpenSSL's ASN.1 implementation that affects versions prior to 1.0.1o and 1.0.2c. This issue stems from improper handling of ASN.1 encoded data structures, specifically when processing ANY fields in crafted serialized data. The vulnerability is categorized under CWE-125 as an out-of-bounds read condition, which can lead to unpredictable behavior and potential code execution. The flaw manifests when OpenSSL encounters malformed ASN.1 data containing negative zero values in ANY fields, creating a scenario where the implementation fails to properly validate input boundaries before attempting memory operations.
The technical exploitation of this vulnerability occurs during the parsing of ASN.1 encoded data structures where the implementation assumes certain field values will be within expected ranges. When malicious data contains negative zero values in ANY fields, the ASN.1 parser performs calculations that result in buffer underflow conditions. This memory corruption can be leveraged by remote attackers to execute arbitrary code on the target system or cause denial of service through application crashes. The vulnerability's impact extends across all OpenSSL versions that implement ASN.1 parsing without proper input validation, affecting cryptographic implementations that rely on ASN.1 encoding for certificate handling, key exchange protocols, and other security-related operations. The attack vector requires the attacker to craft specifically formatted ASN.1 data that can be processed by the vulnerable OpenSSL implementation during normal cryptographic operations.
From an operational perspective, this vulnerability presents a significant risk to systems relying on OpenSSL for secure communications, particularly those handling certificate validation or cryptographic key exchanges. The vulnerability can be exploited in various contexts including web servers, email servers, and any application that uses OpenSSL for TLS/SSL operations. The memory corruption aspect makes exploitation particularly dangerous as it can lead to complete system compromise or denial of service across multiple applications. Security professionals should note that this vulnerability aligns with ATT&CK technique T1059.007 for execution through command and scripting interpreter, as successful exploitation could allow attackers to execute arbitrary code on affected systems. The vulnerability's classification as a buffer underflow also relates to ATT&CK technique T1068 for exploit for privilege escalation, as memory corruption can potentially be leveraged to gain elevated privileges.
Mitigation strategies for CVE-2016-2108 primarily involve immediate patching of OpenSSL implementations to versions 1.0.1o or 1.0.2c, which contain the necessary fixes for proper ASN.1 field validation. Organizations should also implement network monitoring to detect unusual ASN.1 data patterns that might indicate exploitation attempts, particularly in TLS handshakes or certificate processing activities. Additional protective measures include deploying intrusion detection systems that can identify malformed ASN.1 structures and implementing strict input validation for any cryptographic data processed by applications. Security teams should conduct comprehensive vulnerability assessments across all systems using affected OpenSSL versions and consider implementing application-level protections that isolate cryptographic operations from critical system processes. The fix implemented by OpenSSL specifically addresses the negative zero handling in ANY fields by adding proper boundary checks and input validation before memory operations occur, effectively preventing the buffer underflow conditions that led to the vulnerability.