CVE-2016-6304 in Communications EAGLE LNP Application Processor
Summary
by MITRE
Multiple memory leaks in t1_lib.c in OpenSSL before 1.0.1u, 1.0.2 before 1.0.2i, and 1.1.0 before 1.1.0a allow remote attackers to cause a denial of service (memory consumption) via large OCSP Status Request extensions.
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Analysis
by VulDB Data Team • 02/28/2023
The vulnerability identified as CVE-2016-6304 represents a critical memory management flaw within the OpenSSL cryptographic library that affects multiple versions across different release branches. This issue resides in the t1_lib.c file, which handles TLS extension processing, specifically the OCSP Status Request extension mechanism. The vulnerability manifests when OpenSSL processes malformed OCSP Status Request extensions in TLS handshakes, leading to improper memory deallocation during the processing of these extensions. The flaw enables remote attackers to exploit this weakness by crafting specially crafted TLS handshakes containing oversized OCSP Status Request extensions, which causes the application to consume excessive memory resources without proper cleanup. This vulnerability falls under the CWE-401 weakness category, which specifically addresses memory leaks in software systems. The issue is particularly concerning because it affects the core TLS implementation that countless applications and services rely upon for secure communications, making it a prime target for denial of service attacks that can cripple network services.
The technical exploitation of this vulnerability occurs during the TLS handshake process when a client or server receives a certificate status request extension that exceeds normal size parameters. When OpenSSL processes these oversized extensions, the memory allocation routines fail to properly release allocated memory blocks, causing progressive memory consumption over time. The flaw is particularly insidious because it can be triggered without authentication, allowing any remote attacker to send malicious TLS handshakes that will cause the target service to gradually consume all available memory resources. The memory leak occurs due to improper handling of extension data structures where allocated memory for processing OCSP responses is not correctly freed, even when the extension processing fails or encounters malformed data. This type of vulnerability is categorized under the ATT&CK technique T1499.004 which involves network denial of service attacks, specifically targeting resource exhaustion through memory leaks in cryptographic libraries. The vulnerability affects both client and server implementations since both roles process OCSP Status Request extensions during TLS negotiations, making it a widespread concern across all OpenSSL-dependent applications.
The operational impact of CVE-2016-6304 extends far beyond simple service disruption, as it can lead to complete system compromise through resource exhaustion attacks. When exploited successfully, the vulnerability allows attackers to consume system memory at an accelerating rate, eventually leading to application crashes, system instability, and complete denial of service for legitimate users. This vulnerability affects a broad spectrum of services including web servers, email servers, database servers, and any application that relies on OpenSSL for TLS/SSL encryption. The memory consumption pattern is particularly dangerous because it can be sustained over time, allowing attackers to gradually drain system resources without immediate detection. The vulnerability's impact is amplified by the fact that many services are configured to handle multiple concurrent connections, meaning that a single malicious connection can trigger memory leaks across multiple service threads or processes. Organizations running vulnerable OpenSSL versions face significant risk as this vulnerability can be exploited by automated scanning tools to identify and target vulnerable systems, making it a common vector for large-scale denial of service attacks against internet-facing services.
Mitigation strategies for CVE-2016-6304 require immediate patching of affected OpenSSL versions to the recommended secure releases, specifically upgrading to OpenSSL 1.0.1u, 1.0.2i, or 1.1.0a, which contain the necessary memory management fixes. Organizations should implement network-level protections including rate limiting and connection filtering to reduce the impact of potential attacks while patches are being deployed. The fix involves proper memory deallocation routines that ensure all allocated memory for OCSP Status Request extensions is correctly freed regardless of processing outcomes. Security teams should also implement monitoring for unusual memory consumption patterns and establish automated alerting systems to detect potential exploitation attempts. Additionally, organizations can consider implementing certificate stapling as an alternative to OCSP Status Request extensions, which reduces the need for processing these vulnerable extensions. The vulnerability highlights the critical importance of maintaining up-to-date cryptographic libraries and implementing robust security monitoring practices to detect and respond to memory leak exploitation attempts in real-time environments.