CVE-2016-5434 in libalpm
Summary
by MITRE
libalpm, as used in pacman 5.0.1, allows remote attackers to cause a denial of service (infinite loop or out-of-bounds read) via a crafted signature file.
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Analysis
by VulDB Data Team • 10/15/2019
The vulnerability identified as CVE-2016-5434 affects libalpm, the library responsible for package management operations within the pacman package manager version 5.0.1. This flaw exists within the cryptographic signature verification process that pacman employs to validate package integrity and authenticity. The issue manifests when libalpm processes malformed or crafted signature files that contain malformed data structures or unexpected formatting that the library fails to properly handle during verification operations. This vulnerability represents a critical security concern as it can be exploited remotely by attackers who possess the ability to manipulate package repositories or intercept package downloads, potentially compromising system availability through denial of service conditions.
The technical root cause of this vulnerability lies in insufficient input validation and error handling within the signature parsing routines of libalpm. When the library encounters a crafted signature file containing malformed data, it fails to properly validate the structure of the signature before attempting to process it. This leads to two primary failure modes that can result in system compromise: infinite loops where the parsing logic enters recursive or iterative states that never terminate, and out-of-bounds memory reads where the library attempts to access memory locations outside the allocated buffer boundaries. These conditions occur because the code lacks proper bounds checking and validation mechanisms that would normally prevent malformed data from causing unpredictable behavior during cryptographic operations.
The operational impact of CVE-2016-5434 extends beyond simple denial of service scenarios as it can potentially enable more sophisticated attack vectors when combined with other vulnerabilities or when exploited in specific system contexts. An attacker who successfully exploits this vulnerability can cause pacman to consume excessive system resources through infinite loops, potentially leading to system instability or complete service unavailability. In scenarios where the vulnerable system is part of a larger deployment or automated package management infrastructure, this vulnerability could result in cascading failures affecting multiple systems. The out-of-bounds read condition poses additional risks as it may allow attackers to potentially read sensitive memory contents or even facilitate information disclosure attacks that could reveal system state or cryptographic keys.
From a cybersecurity framework perspective, this vulnerability maps to CWE-129 Input Validation and Bounds Checking and CWE-691 Uncontrolled Resource Consumption, both of which are categorized under the broader weakness types that affect software integrity and resource management. The attack surface aligns with ATT&CK technique T1059 Command and Scripting Interpreter where an attacker might leverage a compromised package management system to execute malicious commands, and T1499 System Shutdown/Reboot which could be achieved through resource exhaustion attacks. The vulnerability also represents a failure in the principle of least privilege and defense in depth, as the package manager should have robust error handling to prevent malformed data from causing system-wide failures.
Mitigation strategies for CVE-2016-5434 should focus on immediate patching of affected systems, with the most effective solution being the upgrade to pacman version 5.0.2 or later where the vulnerability has been addressed through improved input validation and error handling in the signature verification process. Organizations should also implement network-level controls to monitor and restrict access to package repositories, ensuring that only authenticated and trusted sources can provide packages to systems. Additional defensive measures include implementing automated vulnerability scanning that can detect and alert on potentially malformed signature files, as well as establishing robust monitoring for unusual resource consumption patterns that might indicate exploitation attempts. System administrators should also consider implementing package integrity verification checks that can detect and prevent installation of packages with corrupted or malformed signatures, providing an additional layer of protection against this and similar vulnerabilities.