CVE-2021-45720 in lru Crate
Summary
by MITRE • 12/27/2021
An issue was discovered in the lru crate before 0.7.1 for Rust. The iterators have a use-after-free, as demonstrated by an access after a pop operation.
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Analysis
by VulDB Data Team • 12/30/2021
The vulnerability identified as CVE-2021-45720 represents a critical memory safety issue within the lru crate version 0.7.1 and earlier, specifically affecting Rust applications that utilize the lru cache implementation. This flaw manifests as a use-after-free condition that occurs during iterator operations, creating a potential vector for memory corruption and arbitrary code execution. The lru crate serves as a fundamental component in many Rust applications, providing a least recently used cache implementation that is widely adopted for its efficiency in managing memory resources. The vulnerability impacts systems where applications rely on iterator methods following pop operations, creating a dangerous state where memory that has been freed is still being accessed or referenced.
The technical flaw stems from improper memory management within the iterator implementation of the lru crate, where the iterator maintains references to memory locations that are subsequently freed when a pop operation occurs. This creates a classic use-after-free scenario that is categorized under CWE-416, which specifically addresses the use of memory after it has been freed. The vulnerability manifests when an iterator is created and then used after a pop operation has been performed on the same cache instance, causing the iterator to reference deallocated memory. This behavior violates fundamental memory safety principles and can lead to unpredictable application behavior, crashes, or potentially exploitable conditions. The issue is particularly concerning in systems where memory corruption could be leveraged for privilege escalation or denial of service attacks.
The operational impact of CVE-2021-45720 extends beyond simple application instability, as it affects any Rust application that utilizes the affected lru crate version and implements iterator operations following cache modifications. Attackers could potentially exploit this vulnerability to execute arbitrary code, escalate privileges, or cause system crashes that result in denial of service. The vulnerability is particularly dangerous in server applications, embedded systems, or any environment where memory safety is critical, as the use-after-free condition could be systematically exploited to gain unauthorized access or compromise system integrity. Applications using the lru crate for caching mechanisms, particularly those handling sensitive data or operating in security-critical environments, face significant risk from this flaw. The vulnerability's exploitation requires minimal conditions, making it a high-priority concern for system administrators and security teams responsible for maintaining Rust-based applications.
Mitigation strategies for CVE-2021-45720 primarily involve upgrading to version 0.7.1 or later of the lru crate, which contains the necessary patches to address the use-after-free condition. Organizations should conduct immediate vulnerability assessments to identify all systems and applications that utilize the affected crate version and prioritize patching operations accordingly. Additionally, developers should review their code implementations to ensure proper iterator usage patterns and avoid scenarios where iterators might be used after cache modifications. The remediation process should include comprehensive testing to verify that the patch resolves the memory safety issue without introducing regressions in application functionality. System monitoring should be enhanced to detect any anomalous behavior that might indicate exploitation attempts, and security teams should implement continuous vulnerability management processes to identify and address similar issues in other third-party dependencies. This vulnerability underscores the importance of maintaining up-to-date dependencies and implementing robust memory safety practices in modern software development environments.