CVE-2018-20997 in OpenSSL Crate
Summary
by MITRE
An issue was discovered in the openssl crate before 0.10.9 for Rust. A use-after-free occurs in CMS Signing.
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Analysis
by VulDB Data Team • 12/04/2023
The vulnerability identified as CVE-2018-20997 represents a critical use-after-free flaw within the openssl crate version 0.10.8 and earlier for the rust programming language. This issue specifically manifests during CMS (Cryptographic Message Syntax) signing operations, where memory management errors create exploitable conditions that could lead to arbitrary code execution or system compromise. The openssl crate serves as a fundamental cryptographic library for rust applications, making this vulnerability particularly concerning given its widespread adoption across the rust ecosystem. The flaw stems from improper memory deallocation practices during the CMS signing process, where freed memory regions are subsequently accessed, creating opportunities for attackers to manipulate program execution flow through memory corruption techniques.
The technical nature of this vulnerability aligns with CWE-416, which describes the use of freed memory condition, and represents a classic example of memory safety issues that have plagued many cryptographic libraries over the years. During CMS signing operations, the openssl crate allocates memory for cryptographic structures and then frees them upon completion of the signing process. However, in certain code paths, the application continues to reference these freed memory locations, leading to undefined behavior that can be exploited by malicious actors. The vulnerability specifically impacts the CMS signing functionality within the openssl crate, which is used for creating and verifying digital signatures in accordance with pkcs#7 standards and other cryptographic protocols. This use-after-free condition creates a window of opportunity for attackers to inject malicious code or manipulate program execution, potentially leading to complete system compromise.
The operational impact of CVE-2018-20997 extends beyond simple memory corruption, as it affects any rust application that utilizes the openssl crate for CMS signing operations. Applications ranging from web servers handling SSL/TLS certificates to cryptographic tools performing digital signature validation become vulnerable to exploitation. The attack surface includes any system where rust-based applications rely on the openssl crate for cryptographic operations, particularly those involving certificate management, secure communications, or digital signature verification. Given that many rust applications utilize this crate for fundamental security operations, the potential for widespread exploitation exists, especially in environments where applications process untrusted input or perform cryptographic operations on sensitive data. The vulnerability's exploitation requires specific conditions related to the CMS signing process and memory allocation patterns, but once achieved, could result in complete system compromise or data breach.
Mitigation strategies for CVE-2018-20997 focus primarily on upgrading to openssl crate version 0.10.9 or later, which contains the necessary memory management fixes to prevent the use-after-free condition. Organizations should conduct comprehensive vulnerability assessments to identify all rust applications utilizing the affected crate and prioritize remediation efforts accordingly. Additionally, implementing runtime protections such as address space layout randomization and stack canaries can help reduce exploitability, though these measures are considered defensive in nature and do not address the root cause. The fix implemented in version 0.10.9 involves proper memory lifecycle management during CMS signing operations, ensuring that memory regions are not accessed after deallocation. Security teams should also consider monitoring for suspicious network activity or system behavior that might indicate exploitation attempts, as the vulnerability's exploitation typically involves memory corruption techniques that may leave detectable traces in system logs or network traffic patterns. This vulnerability serves as a reminder of the critical importance of memory safety in cryptographic libraries and the need for rigorous testing and code review processes in security-critical components.