CVE-2010-0634 in flex
Summary
by MITRE
Unspecified vulnerability in Fast Lexical Analyzer Generator (flex) before 2.5.35 has unknown impact and attack vectors.
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Analysis
by VulDB Data Team • 04/30/2026
The vulnerability identified as CVE-2010-0634 affects the Fast Lexical Analyzer Generator commonly known as flex, which is a widely used tool for generating lexical analyzers or scanners in software development. This tool is essential for parsing input text and identifying tokens that form the basis of programming languages, data formats, and various applications requiring text processing. The vulnerability exists in versions prior to 2.5.35, indicating that the issue was present in a significant portion of the flex toolchain that developers relied upon for creating lexical analyzers across multiple platforms and applications.
The technical nature of this unspecified vulnerability within flex represents a critical security flaw that could potentially allow attackers to exploit the tool during the compilation process of software applications. When developers use flex to generate lexical analyzers, they typically provide input files containing regular expressions and action code that define how the scanner should process input data. The unspecified nature of the vulnerability suggests that it could manifest in various ways including buffer overflows, memory corruption issues, or code injection opportunities that arise during the parsing and generation phases of the flex tool itself. This type of vulnerability in a code generation tool poses a particularly serious risk because it can affect the integrity of the entire software development process.
The operational impact of this vulnerability extends beyond simple code generation failures, potentially enabling attackers to compromise the build environment of software projects that utilize flex. When an attacker can exploit this vulnerability during the compilation phase, they might be able to inject malicious code into the generated lexical analyzers, which would then execute within the context of applications using those analyzers. This represents a sophisticated attack vector that could leverage the trust placed in legitimate development tools to compromise downstream applications. The vulnerability could also enable privilege escalation scenarios if the flex tool is executed with elevated permissions during automated build processes or continuous integration environments.
According to CWE classification, this vulnerability likely falls under categories related to code injection, buffer overflows, or memory corruption issues that are commonly associated with tools processing untrusted input data. The ATT&CK framework would categorize this under software supply chain compromises or development environment compromises, where adversaries target the tools used in the creation of legitimate software to gain access to downstream systems. Organizations using flex in their development workflows may be vulnerable to attacks that exploit this weakness, particularly in environments where build systems are not properly isolated or where the tool is run with elevated privileges.
The mitigation strategy for this vulnerability requires immediate upgrading of flex installations to version 2.5.35 or later, which would contain the necessary patches to address the unspecified security flaw. System administrators and development teams should conduct comprehensive audits of their build environments to identify all instances of vulnerable flex versions and ensure proper patch management protocols are in place. Additionally, implementing strict input validation measures for flex input files and establishing secure build environments with proper privilege separation can help reduce the risk of exploitation. Organizations should also consider implementing continuous monitoring of their development toolchains to detect any unauthorized modifications or suspicious activities that might indicate exploitation attempts targeting such vulnerabilities.