CVE-2017-9304 in YARA
Summary
by MITRE
libyara/re.c in the regexp module in YARA 3.5.0 allows remote attackers to cause a denial of service (stack consumption) via a crafted rule that is mishandled in the _yr_re_emit function.
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Analysis
by VulDB Data Team • 12/07/2022
The vulnerability identified as CVE-2017-9304 resides within the YARA regexp module, specifically in the libyara/re.c file where the _yr_re_emit function fails to properly handle certain crafted regular expression rules. This flaw represents a classic stack-based denial of service vulnerability that can be exploited by remote attackers to consume excessive system resources through carefully constructed malicious input patterns. YARA, a widely used tool for identifying and classifying malware samples based on textual or binary patterns, processes these regular expressions as part of its rule evaluation mechanism, making this vulnerability particularly concerning for security operations that rely on YARA for threat detection.
The technical implementation of this vulnerability stems from inadequate input validation and resource management within the regular expression compilation and execution pipeline. When YARA processes a specially crafted rule containing malformed or overly complex regular expression patterns, the _yr_re_emit function enters an infinite loop or excessively consumes stack memory during the compilation phase. This behavior aligns with CWE-400, which categorizes unchecked resource consumption as a significant security weakness, and demonstrates how improper handling of user-supplied data can lead to system instability. The vulnerability specifically affects YARA version 3.5.0, where the regular expression engine lacks proper bounds checking and stack depth limitations during pattern analysis.
The operational impact of this vulnerability extends beyond simple service disruption to potentially compromise the integrity of security monitoring systems that depend on YARA for malware detection. Attackers can exploit this weakness by submitting malicious rules to YARA-based systems, causing the application to consume excessive stack memory until system resources are exhausted and the service becomes unavailable. This denial of service scenario can be particularly damaging in environments where YARA is used for real-time threat hunting, automated malware analysis, or security information and event management systems. The vulnerability's remote exploitation capability means that any system processing external YARA rules, such as web-based malware analysis platforms or collaborative threat intelligence systems, becomes vulnerable to this attack vector.
Mitigation strategies for CVE-2017-9304 should prioritize immediate patching of affected YARA installations to version 3.6.0 or later, where the vulnerability has been addressed through improved input validation and stack memory management. Organizations should implement strict rule validation procedures for any externally submitted YARA rules, including automated sanitization and resource monitoring to detect anomalous memory consumption patterns. The ATT&CK framework categorizes this type of vulnerability under T1499.004, which covers network denial of service attacks, and organizations should consider implementing network segmentation and resource limits to prevent exploitation from affecting critical systems. Additionally, security teams should establish monitoring protocols to detect unusual stack consumption patterns in YARA processes and implement rate limiting for rule processing to prevent exploitation through resource exhaustion attacks.