CVE-2018-21232 in re2c
Summary
by MITRE
re2c before 2.0 has uncontrolled recursion that causes stack consumption in find_fixed_tags.
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Analysis
by VulDB Data Team • 05/06/2025
The vulnerability identified as CVE-2018-21232 affects the re2c tool version 2.0 and earlier, specifically within the find_fixed_tags function where uncontrolled recursion occurs leading to excessive stack consumption. This issue represents a classic stack overflow vulnerability that can be exploited through carefully crafted input patterns that trigger recursive function calls without proper base case validation. The re2c tool is widely used for generating fast lexical analyzers from regular expressions, making this vulnerability particularly concerning for software systems that rely on automated code generation processes. The uncontrolled recursion manifests when the tool processes certain regular expression patterns that result in deeply nested recursive calls during the fixed tag identification phase of lexical analysis generation.
The technical flaw stems from inadequate recursion depth checking within the find_fixed_tags function implementation. When processing specific regular expression inputs, the algorithm enters into recursive loops where each recursive call consumes stack space without proper termination conditions. This behavior aligns with CWE-674, which describes uncontrolled recursion vulnerabilities where recursive functions lack proper depth limits or termination checks. The vulnerability is particularly dangerous because it can be triggered through input files that are processed by re2c during normal operation, potentially allowing attackers to craft malicious regular expressions that will cause the tool to consume excessive stack memory during compilation. The stack consumption occurs linearly with each recursive call, making it possible to exhaust available stack space and cause program termination or potentially enable more sophisticated attack vectors depending on the execution environment.
The operational impact of this vulnerability extends beyond simple denial of service scenarios, as it can affect software development workflows and build systems that utilize re2c for code generation. Development environments that automatically invoke re2c during compilation processes become vulnerable to exploitation, potentially disrupting continuous integration pipelines and build automation. Attackers could leverage this vulnerability to cause build failures, leading to operational disruptions in software development cycles. In environments where re2c is used to generate critical components of security tools or system utilities, the impact could be more severe as it might compromise the integrity of the entire software supply chain. The vulnerability also presents challenges for automated security scanning tools that might invoke re2c on untrusted input files, creating potential attack surfaces for malicious code injection.
Mitigation strategies should focus on upgrading to re2c version 2.0 or later where the recursion control mechanisms have been implemented. Organizations should also implement input validation measures when processing regular expressions through re2c, particularly in environments where untrusted inputs might be processed. The implementation of stack depth limits and recursion counters within the tool itself provides the most effective defense against this specific vulnerability. Additionally, security teams should monitor build systems for unusual stack consumption patterns and implement proper access controls to prevent unauthorized use of re2c on potentially malicious inputs. This vulnerability demonstrates the importance of proper recursion handling in code generation tools and aligns with ATT&CK technique T1059.007 for execution through code generation tools, emphasizing the need for comprehensive security controls around automated code generation processes.