CVE-2016-0797 in Xcode
Summary
by MITRE
Multiple integer overflows in OpenSSL 1.0.1 before 1.0.1s and 1.0.2 before 1.0.2g allow remote attackers to cause a denial of service (heap memory corruption or NULL pointer dereference) or possibly have unspecified other impact via a long digit string that is mishandled by the (1) BN_dec2bn or (2) BN_hex2bn function, related to crypto/bn/bn.h and crypto/bn/bn_print.c.
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Analysis
by VulDB Data Team • 09/28/2022
The vulnerability identified as CVE-2016-0797 represents a critical security flaw in OpenSSL cryptographic library versions prior to 1.0.1s and 1.0.2g. This issue manifests through integer overflow conditions that occur within the BN_dec2bn and BN_hex2bn functions, which are fundamental components responsible for converting decimal and hexadecimal string representations into big number objects. The flaw specifically arises when these functions process exceptionally long digit strings that exceed the intended integer limits, creating conditions that can lead to unpredictable system behavior. The vulnerability falls under the CWE-190 category of integer overflow, which is a well-documented class of weaknesses that can result in memory corruption and system instability.
The technical implementation of this vulnerability involves the manipulation of integer variables within the big number arithmetic functions that handle cryptographic operations. When OpenSSL processes digit strings that exceed the maximum representable integer values, the arithmetic operations involved in the conversion process can overflow, causing the system to allocate insufficient memory or attempt to access invalid memory locations. This overflow condition can manifest in two primary ways: heap memory corruption when the system attempts to write beyond allocated memory boundaries, or NULL pointer dereference when the system tries to access memory addresses that have not been properly initialized. The functions BN_dec2bn and BN_hex2bn are particularly susceptible because they must dynamically calculate memory requirements based on input string length, creating a direct pathway for attackers to exploit integer overflow conditions through carefully crafted input data.
The operational impact of CVE-2016-0797 extends beyond simple denial of service conditions, potentially enabling more sophisticated attack vectors that align with ATT&CK technique T1499.3 for network denial of service. Remote attackers can leverage this vulnerability to cause system instability through heap corruption, which may result in application crashes, system restarts, or in more severe cases, potentially allow for privilege escalation or arbitrary code execution. The vulnerability affects a wide range of cryptographic applications that rely on OpenSSL for secure communications, including web servers, email systems, and any software that implements SSL/TLS encryption. The nature of the flaw means that even seemingly benign input strings can trigger the overflow conditions, making it particularly dangerous as it can be exploited through normal user interactions without requiring specialized knowledge of the underlying cryptographic functions.
Mitigation strategies for this vulnerability require immediate patching of OpenSSL installations to versions 1.0.1s or 1.0.2g and later, which contain the necessary fixes to properly validate input string lengths before performing arithmetic operations. Organizations should also implement input validation measures at application layers that consume OpenSSL functions, ensuring that digit strings passed to BN_dec2bn and BN_hex2bn are properly bounded and validated before processing. The fix implemented by OpenSSL developers addresses the root cause by introducing proper integer overflow checks and bounds validation within the affected functions, preventing the arithmetic operations from exceeding maximum representable values. System administrators should conduct comprehensive vulnerability assessments to identify all systems using vulnerable OpenSSL versions and prioritize remediation efforts based on the criticality of affected applications. Additionally, monitoring systems should be configured to detect unusual patterns in cryptographic function usage that might indicate exploitation attempts, as the vulnerability can be leveraged in combination with other techniques to create more sophisticated attack scenarios.