CVE-2016-4355 in Libksba
Summary
by MITRE
Multiple integer overflows in ber-decoder.c in Libksba before 1.3.3 allow remote attackers to cause a denial of service (crash) via crafted BER data, which leads to a buffer overflow.
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Analysis
by VulDB Data Team • 08/23/2022
The vulnerability identified as CVE-2016-4355 represents a critical security flaw within the Libksba library, specifically affecting versions prior to 1.3.3. This issue resides in the ber-decoder.c component and manifests as multiple integer overflows that can be exploited by remote attackers to execute denial of service attacks. The vulnerability stems from the library's insufficient validation of input data when processing binary encoded representation data, creating a pathway for malicious actors to craft specially designed BER (Basic Encoding Rules) data that triggers unexpected behavior in the decoding process.
The technical implementation of this vulnerability involves integer overflow conditions that occur during the parsing of BER encoded data structures. When the ber-decoder.c module processes malformed input, it fails to properly validate integer values that determine buffer allocation sizes, leading to scenarios where calculated buffer dimensions exceed available memory boundaries. This mismanagement of integer values creates conditions where subsequent memory operations attempt to write beyond allocated buffer limits, resulting in buffer overflow conditions. The vulnerability specifically affects the handling of length fields within BER structures, where attacker-controlled values can cause arithmetic overflow during size calculations, ultimately leading to memory corruption and application instability.
From an operational perspective, this vulnerability presents significant risks to systems that rely on Libksba for cryptographic operations and certificate processing. The remote exploitation capability means that attackers can potentially disrupt services without requiring local access or authentication credentials, making it particularly dangerous in networked environments. Systems utilizing the affected library for email encryption, certificate management, or digital signature verification become vulnerable to crashes that can render services unavailable, effectively creating a denial of service condition. The impact extends beyond simple service disruption as the buffer overflow conditions could potentially be leveraged for more sophisticated attacks if additional vulnerabilities exist within the same codebase or if the application fails to properly handle memory corruption scenarios.
The vulnerability aligns with CWE-190, which categorizes integer overflow conditions as a fundamental weakness in software design that can lead to memory corruption and unpredictable behavior. From an adversarial perspective, this flaw maps to multiple ATT&CK techniques including T1499.004 for network denial of service and potentially T1059 for command execution if the application crashes in a manner that allows further exploitation. The attack vector requires only the ability to send crafted BER data to the vulnerable system, making it particularly attractive to threat actors seeking to disrupt services or create chaos in targeted environments. Organizations using affected versions of Libksba should prioritize immediate patching and remediation efforts to prevent potential exploitation.
Mitigation strategies for CVE-2016-4355 primarily focus on upgrading to Libksba version 1.3.3 or later, which contains the necessary patches to address the integer overflow conditions. System administrators should conduct thorough inventory assessments to identify all systems utilizing vulnerable library versions and implement comprehensive patch management procedures. Additional defensive measures include implementing network segmentation to limit exposure of systems to untrusted BER data sources, deploying intrusion detection systems to monitor for suspicious data patterns, and establishing robust application monitoring to detect service disruptions. Organizations should also consider implementing input validation controls at network boundaries to filter out potentially malicious BER data before it reaches vulnerable applications. The fix implemented in version 1.3.3 typically involves strengthening integer validation logic, adding proper bounds checking for buffer allocation calculations, and implementing more robust error handling for malformed input data.