The vulnerability identified as CVE-2021-21295 affects the Netty framework, an open-source, asynchronous event-driven network application framework used for the rapid development of high-performance protocol servers and clients. The vulnerability exists in the HTTP/2 codec of Netty, specifically in versions prior to 4.1.60.Final, and allows for request smuggling when the Content-Length header is present in the original HTTP/2 request.
This vulnerability is classified as medium severity with a CVSS score of 5.9. The significance lies in its potential impact on the integrity of the data being processed. If exploited, attackers can smuggle requests, which may lead to unauthorized actions on the backend systems.
Organizations utilizing affected versions of Netty should prioritize patching immediately. The fix has been addressed in version 4.1.60.Final. Users can implement a temporary mitigation strategy by validating the Content-Length header through a custom ChannelInboundHandler.
The risk to organizations includes potential unauthorized access to backend systems and manipulation of data, emphasizing the need for timely remediation.
Vulnerability Details
The official description states that in Netty (io.netty:netty-codec-http2) before version 4.1.60.Final, a vulnerability enables request smuggling due to the lack of validation of the Content-Length header by the Http2MultiplexHandler as it is propagated. If the request is proxied through as HTTP/1.1, the assumptions about validation can lead to exploitation.
The vulnerability has a CVSS score of 5.9, indicating medium severity, which means that while the attack complexity is high and no privileges are required for exploitation, the potential integrity impact is significant. The affected versions include those prior to 4.1.60.Final.
Technical Analysis
The root cause of this vulnerability lies in how Netty handles the conversion of HTTP/2 requests to HTTP/1.1. The conversion process via the Http2StreamFrameToHttpObjectCodec does not enforce validation on the Content-Length header, which can lead to scenarios where an attacker can craft malicious requests that manipulate backend processing.
The attack vector is network-based, with a high attack complexity, meaning that an attacker must have a deep understanding of the HTTP/2 and HTTP/1.1 protocols and how they interoperate within the Netty framework. This vulnerability does not require user interaction, making it more dangerous.
The potential impacts include a lack of confidentiality because the attacker can smuggle requests without being detected, a high integrity impact due to possible data manipulation, and no availability impact.
Risk & Impact Analysis
Organizations using affected versions of Netty face significant risk if they do not address this vulnerability. The nature of request smuggling attacks can lead to unauthorized access to sensitive data or disruption of service as attackers could manipulate requests to achieve unauthorized actions.
Given the CVSS score of 5.9, organizations should assess their exposure to this vulnerability and prioritize remediation strategies appropriately. The urgency for patching can be classified as high to ensure the integrity of systems handling HTTP/2 requests.
Exploitation Status
Signal | Status |
|---|---|
Known Exploit | No |
Public PoC | No |
Actively Exploited | No |
Ransomware Use | No |
Affected Versions
The vulnerability affects all versions of Netty prior to version 4.1.60.Final. It is also relevant for users of certain configurations of other products that depend on Netty, including NetApp's OnCommand API Services and Oracle's communications cloud native core policy.
Mitigation & Remediation
To mitigate the risks associated with CVE-2021-21295, organizations should upgrade to Netty version 4.1.60.Final or later. If an immediate upgrade is not possible, users can implement a custom ChannelInboundHandler to validate the Content-Length header manually by placing it in the ChannelPipeline behind the Http2StreamFrameToHttpObjectCodec.
Additionally, organizations should consider performing a thorough security assessment and engage in application security assessments to identify any further vulnerabilities within their systems.
Detection Guidance
Organizations should monitor their logs for any anomalies related to HTTP requests, specifically looking for unusual patterns that may indicate request smuggling. Additionally, network signatures should be updated to detect potential exploit attempts.
AppSecure Threat Intelligence Insight
CVE-2021-21295 highlights the importance of validating HTTP headers in network protocols. As organizations increasingly rely on frameworks like Netty for high-performance applications, the need for robust security practices becomes critical. Security teams should ensure proper validation mechanisms are in place, particularly when dealing with protocol conversions.
To strengthen defenses, organizations can engage in red teaming exercises to simulate real-world attack scenarios and identify potential weaknesses within their application architectures.
Furthermore, organizations can adopt continuous security practices, utilizing solutions like continuous penetration testing to maintain a proactive security posture.
Lastly, organizations should engage in regular security training for their development teams, focusing on best practices for secure coding and vulnerability management.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
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