CVE-2016-4970 in Netty
Summary
by MITRE
handler/ssl/OpenSslEngine.java in Netty 4.0.x before 4.0.37.Final and 4.1.x before 4.1.1.Final allows remote attackers to cause a denial of service (infinite loop).
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Analysis
by VulDB Data Team • 11/29/2022
The vulnerability identified as CVE-2016-4970 affects the Netty networking framework, specifically within the SSL implementation component located at handler/ssl/OpenSslEngine.java. This issue represents a critical denial of service flaw that can be exploited by remote attackers to disrupt service availability. The vulnerability exists in Netty versions 4.0.x prior to 4.0.37.Final and 4.1.x prior to 4.1.1.Final, making it a widespread concern across multiple release lines of this popular Java networking library. The flaw manifests as an infinite loop condition that can be triggered through specific SSL handshake sequences, causing the affected application to consume excessive CPU resources and potentially crash or become unresponsive.
The technical root cause of this vulnerability stems from improper handling of SSL handshake processing within the OpenSslEngine implementation. When certain malformed or specially crafted SSL packets are received during the handshake process, the engine enters a condition where it repeatedly processes the same data without making forward progress. This infinite loop occurs due to inadequate boundary checks and state management during SSL protocol negotiation. The flaw is particularly dangerous because it can be triggered remotely without requiring authentication or special privileges, making it an attractive target for denial of service attacks. According to CWE classification, this vulnerability maps to CWE-835: Loop with Unreachable Exit Condition (Infinite Loop), which is a well-known category of software defects that can lead to system instability and resource exhaustion.
The operational impact of CVE-2016-4970 extends beyond simple service disruption to potentially compromise entire application availability and system stability. Applications built on Netty that handle SSL connections, including web servers, application servers, and microservices, become vulnerable to this attack vector. The infinite loop consumes CPU cycles continuously, which can lead to resource exhaustion and cascading failures in systems where multiple vulnerable components exist. Attackers can exploit this vulnerability by establishing SSL connections to target systems and sending carefully crafted handshake messages that trigger the loop condition. This type of attack can be particularly devastating in high-traffic environments where the CPU consumption can quickly overwhelm system resources, leading to complete service unavailability. The vulnerability aligns with ATT&CK technique T1499.004: Endpoint Denial of Service, which focuses on disrupting endpoint services through resource exhaustion.
Mitigation strategies for CVE-2016-4970 primarily involve upgrading to patched versions of Netty where the infinite loop condition has been resolved. Organizations should prioritize updating their Netty dependencies to versions 4.0.37.Final or later for the 4.0.x line, and 4.1.1.Final or later for the 4.1.x line. Additionally, implementing network-level protections such as rate limiting and connection monitoring can help detect and prevent exploitation attempts. Security teams should also consider deploying intrusion detection systems that can identify anomalous SSL handshake patterns indicative of this attack. The vulnerability highlights the importance of thorough testing of SSL/TLS implementations and proper input validation in cryptographic libraries. Organizations using older Netty versions should conduct immediate vulnerability assessments and implement temporary workarounds while planning for the necessary upgrades to ensure complete protection against this and similar classes of denial of service vulnerabilities.