CVE-2020-36458 in lexer Crate
Summary
by MITRE • 08/08/2021
An issue was discovered in the lexer crate through 2020-11-10 for Rust. For ReaderResult, there is an implementation of Sync with a trait bound of T: Send, E: Send.
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Analysis
by VulDB Data Team • 08/14/2021
The vulnerability identified as CVE-2020-36458 resides within the lexer crate for Rust, a critical component in parsing and tokenizing text input for various applications. This issue specifically affects versions of the crate released through November 10, 2020, creating a potential security risk for systems that rely on proper synchronization mechanisms during concurrent execution. The lexer crate serves as a foundational element in Rust's ecosystem, particularly for parsing operations in compilers, interpreters, and text processing applications that require robust tokenization capabilities. The flaw manifests in how the ReaderResult type handles synchronization guarantees, which directly impacts the safety and correctness of concurrent operations within Rust programs that utilize this crate.
The technical implementation flaw involves the ReaderResult type's synchronization behavior where it implements the Sync trait with specific constraints on its generic parameters. The trait bound requires that T: Send and E: Send, which creates an inconsistency in the synchronization model. While Send guarantees that a type can be safely transferred between threads, Sync ensures safe shared access across threads, yet the current implementation fails to properly enforce these guarantees. This mismatch creates a potential race condition scenario where concurrent access to ReaderResult instances may not be properly synchronized, leading to undefined behavior or memory safety violations. The vulnerability stems from the improper relationship between these synchronization traits, where the implementation assumes that Send alone is sufficient for safe concurrent access, which contradicts fundamental Rust safety principles and the expected behavior of the Sync trait.
The operational impact of this vulnerability extends across multiple domains where Rust-based applications utilize the affected lexer crate, particularly in compiler toolchains, language servers, and text processing systems that handle concurrent input streams. Attackers could potentially exploit this weakness to introduce memory corruption, data races, or other concurrency-related issues that compromise system stability and security. Applications relying on the lexer crate for parsing user input, configuration files, or code analysis may become vulnerable to race conditions that could be leveraged for privilege escalation or denial of service attacks. The vulnerability is particularly concerning in multi-threaded environments where the lexer processes multiple input streams simultaneously, as the improper synchronization could lead to unpredictable behavior that manifests as crashes, incorrect parsing results, or even security breaches in applications that depend on the correctness of tokenization.
Mitigation strategies for CVE-2020-36458 should prioritize updating to the latest version of the lexer crate where the synchronization implementation has been corrected to properly enforce both Send and Sync bounds. System administrators and developers should conduct thorough code reviews to identify any applications that depend on the affected crate version and ensure proper dependency updates are implemented across all environments. The fix typically involves correcting the trait bounds to properly require both Send and Sync for the generic parameters, ensuring that ReaderResult instances can be safely shared across threads without introducing race conditions. Additionally, implementing proper testing for concurrent access patterns and utilizing Rust's built-in memory safety features such as borrow checking and lifetime management can help prevent similar issues in other components of the codebase. Organizations should also consider implementing automated dependency scanning tools to identify and remediate similar vulnerabilities in their software supply chains, aligning with industry standards such as those recommended in the CWE catalog for concurrency-related issues and the ATT&CK framework's approach to software supply chain attacks.