CVE-2016-4353 in Libksba
Summary
by MITRE
ber-decoder.c in Libksba before 1.3.3 does not properly handle decoder stack overflows, which allows remote attackers to cause a denial of service (abort) via crafted BER data.
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Analysis
by VulDB Data Team • 08/23/2022
The vulnerability identified as CVE-2016-4353 resides within the ber-decoder.c component of Libksba version 1.3.2 and earlier, representing a critical security flaw that affects the proper handling of BER (Basic Encoding Rules) data structures. This issue manifests as an improper management of decoder stack operations during the processing of malformed input data, creating a condition where the application fails to maintain proper stack boundaries during decoding processes. The vulnerability specifically targets the stack overflow handling mechanisms within the BER decoding implementation, which is a fundamental component of the Libksba library used for handling X.509 certificates and other cryptographic data formats.
The technical flaw stems from insufficient bounds checking and stack management during the decoding of BER-encoded data structures, where the decoder fails to properly validate the depth of nested structures or the overall stack usage during recursive parsing operations. When maliciously crafted BER data is processed, the decoder attempts to allocate stack space for nested elements without adequate validation of stack limits, leading to stack overflow conditions that cause the application to abort unexpectedly. This behavior aligns with CWE-121, which describes stack-based buffer overflow conditions, and specifically demonstrates improper handling of stack operations during data parsing. The vulnerability operates at the protocol level where BER data structures are decoded, making it particularly dangerous as it can be triggered through normal cryptographic operations involving certificate processing.
The operational impact of this vulnerability extends beyond simple denial of service, as it can be exploited by remote attackers to disrupt services that rely on Libksba for certificate handling and cryptographic operations. Systems utilizing this library for X.509 certificate validation, PKCS#11 operations, or other cryptographic functions become vulnerable to exploitation, potentially causing cascading failures in security infrastructure. The abort condition triggered by the stack overflow can lead to service unavailability, making it particularly dangerous in production environments where certificate validation is critical for authentication and secure communications. Attackers can craft specific BER-encoded payloads that will cause the application to crash when processing legitimate certificate data, effectively creating a remote denial of service condition that can be exploited across network boundaries. This vulnerability directly maps to ATT&CK technique T1499.004, which describes network denial of service attacks, and represents a classic example of how improper input validation can lead to service disruption.
Mitigation strategies for CVE-2016-4353 focus primarily on upgrading to Libksba version 1.3.3 or later, which includes proper stack overflow handling and bounds checking mechanisms. Organizations should conduct thorough inventory assessments to identify all systems utilizing Libksba, particularly those involved in certificate processing, PKI operations, or cryptographic services. Additionally, implementing input validation controls and monitoring for unusual stack allocation patterns can provide early detection of potential exploitation attempts. The fix implemented in version 1.3.3 addresses the root cause by introducing proper stack depth tracking and validation mechanisms, ensuring that decoder operations maintain appropriate stack boundaries during BER data processing. System administrators should also consider implementing network segmentation and access controls to limit exposure of systems that process certificate data, reducing the attack surface for potential exploitation of this vulnerability.