CVE-2017-5923 in YARA
Summary
by MITRE
libyara/grammar.y in YARA 3.5.0 allows remote attackers to cause a denial of service (heap-based out-of-bounds read and application crash) via a crafted rule that is mishandled in the yara_yyparse function.
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Analysis
by VulDB Data Team • 11/24/2022
The vulnerability identified as CVE-2017-5923 resides within the YARA threat detection engine version 3.5.0, specifically in the libyara/grammar.y component that governs the parsing of YARA rules. This issue manifests as a heap-based out-of-bounds read condition that occurs when the yara_yyparse function processes malformed or crafted YARA rules. The flaw represents a critical security weakness that can be exploited remotely by malicious actors to disrupt the normal operation of systems utilizing YARA for threat hunting and malware detection.
The technical implementation of this vulnerability stems from insufficient input validation within the YARA rule parser's grammar definition file. When an attacker crafts a specially designed YARA rule that triggers the yara_yyparse function, the parser fails to properly bounds-check memory accesses during the parsing process. This leads to the application reading memory locations beyond the allocated heap buffer boundaries, resulting in undefined behavior that ultimately causes application crashes and system instability. The vulnerability is classified under CWE-125 as an out-of-bounds read condition, which is a well-documented weakness in memory management that can lead to denial of service scenarios and potentially more severe exploitation vectors.
The operational impact of this vulnerability extends beyond simple service disruption, as it can severely compromise the effectiveness of security operations that rely on YARA for malware analysis and threat detection. Organizations deploying YARA-based solutions for endpoint protection, network monitoring, or incident response may find their security infrastructure rendered temporarily unusable when encountering maliciously crafted YARA rules. This vulnerability particularly affects systems where YARA is used in automated scanning processes or where rule sets are dynamically loaded from untrusted sources, creating potential attack vectors through rule injection or manipulation.
The exploitation of CVE-2017-5923 aligns with ATT&CK technique T1059.007 for execution through scripting and T1499.004 for network denial of service. Security practitioners should consider this vulnerability as part of broader defensive strategies against adversarial threat hunting techniques that may attempt to disrupt security tooling. The remediation approach involves upgrading to YARA version 3.6.0 or later, where the parsing logic has been corrected to properly handle malformed input and prevent out-of-bounds memory accesses. Organizations should also implement strict rule validation procedures and consider sandboxing environments for rule processing to minimize the impact of potential exploitation attempts.