A denial-of-service vulnerability was found in the Drools DRL expression parser (org.drools:drools-drl-parser). The ANTLR4-generated DRL expression grammar parses parenthesised sub-expressions through mutually recursive descent rules with no limit on nesting depth. When a deeply nested parenthesised constraint expression (approximately 300-400 levels) is parsed, the parsing thread exhausts its stack and a java.lang.StackOverflowError is raised and propagates out of the parse call instead of being converted into a DroolsParserException. An actor able to supply a crafted DRL expression to an application that parses untrusted DRL can cause a denial of service.
Advisories

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Fixes

Solution

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Workaround

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History

Tue, 03 Nov 2026 00:30:00 +0000

Type Values Removed Values Added
Description A denial-of-service vulnerability was found in the Drools DRL expression parser (org.drools:drools-drl-parser). The ANTLR4-generated DRL expression grammar parses parenthesised sub-expressions through mutually recursive descent rules with no limit on nesting depth. When a deeply nested parenthesised constraint expression (approximately 300-400 levels) is parsed, the parsing thread exhausts its stack and a java.lang.StackOverflowError is raised and propagates out of the parse call instead of being converted into a DroolsParserException. An actor able to supply a crafted DRL expression to an application that parses untrusted DRL can cause a denial of service.
Title drools-drl-parser: uncontrolled recursion when parsing deeply nested parenthesised expressions leads to denial of service (StackOverflowError)
Weaknesses CWE-674
References
Metrics threat_severity

None

cvssV3_1

{'score': 5.3, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L'}

threat_severity

Moderate


Projects

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cve-icon MITRE

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cve-icon Vulnrichment

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cve-icon NVD

No data.

cve-icon Redhat

Severity : Moderate

Publid Date: 2026-11-02T00:00:00Z

Links: CVE-2026-120420 - Bugzilla

cve-icon OpenCVE Enrichment

Updated: 2026-11-03T01:45:09Z

Weaknesses