CVE-2016-4574 in Libksba
Summary
by MITRE
Off-by-one error in the append_utf8_value function in the DN decoder (dn.c) in Libksba before 1.3.4 allows remote attackers to cause a denial of service (out-of-bounds read) via invalid utf-8 encoded data. NOTE: this vulnerability exists because of an incomplete fix for CVE-2016-4356.
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Analysis
by VulDB Data Team • 08/23/2022
The vulnerability described in CVE-2016-4574 represents a critical off-by-one error within the Libksba library's DN (Distinguished Name) decoder component. This flaw specifically affects the append_utf8_value function located in the dn.c file and exists in Libksba versions prior to 1.3.4. The vulnerability arises from an incomplete remediation of a previously discovered issue, CVE-2016-4356, which demonstrates the complexity of addressing memory safety issues in cryptographic libraries. The root cause stems from improper bounds checking during UTF-8 data processing, where the function fails to properly validate the boundaries of input data when appending UTF-8 encoded values to distinguished names. This error condition creates a scenario where an attacker can manipulate input data to trigger an out-of-bounds memory read operation, effectively allowing for a denial of service attack against systems utilizing the affected library.
The technical implementation of this vulnerability involves the manipulation of UTF-8 encoded data within the DN decoding process, where the append_utf8_value function does not correctly handle boundary conditions during character validation and processing. When malformed UTF-8 sequences are processed, the function's off-by-one error causes it to read memory locations beyond the allocated buffer boundaries, potentially leading to information disclosure or system instability. This type of vulnerability falls under CWE-129, which specifically addresses insufficient boundary checking, and represents a classic example of how incomplete fixes can leave systems vulnerable to similar attack vectors. The flaw operates at the intersection of data validation and memory management, where the improper handling of character encoding boundaries creates exploitable conditions that can be leveraged by remote attackers without requiring special privileges or authentication.
The operational impact of CVE-2016-4574 extends beyond simple denial of service, as it represents a potential pathway for more sophisticated attacks within cryptographic environments that rely on Libksba for certificate processing and key management operations. Systems utilizing affected versions of Libksba may experience service interruptions when processing malformed distinguished names, particularly in scenarios involving certificate validation, key extraction, or digital signature operations. The vulnerability affects applications that depend on Libksba for handling X.509 certificates and PKCS#11 operations, which are fundamental components in secure communication protocols, identity management systems, and cryptographic infrastructure. From an ATT&CK framework perspective, this vulnerability aligns with techniques involving denial of service and resource exhaustion, potentially enabling attackers to disrupt services or create conditions for more complex exploitation attempts.
Mitigation strategies for CVE-2016-4574 require immediate patching of affected Libksba installations to version 1.3.4 or later, which contains the complete fix for both CVE-2016-4356 and this specific vulnerability. Organizations should conduct comprehensive inventory assessments to identify all systems utilizing vulnerable Libksba versions and prioritize remediation efforts accordingly. Additionally, implementing input validation controls at application layers can provide defense-in-depth measures, though the primary solution remains the library update. Security monitoring should focus on detecting unusual patterns in certificate processing or authentication failures that might indicate exploitation attempts. The vulnerability serves as a reminder of the importance of thorough vulnerability remediation processes and the potential risks associated with partial fixes that do not address all related attack vectors within complex cryptographic libraries.