CVE-2021-21607 in Jenkins
Summary
by MITRE • 01/14/2021
Jenkins 2.274 and earlier, LTS 2.263.1 and earlier does not limit sizes provided as query parameters to graph-rendering URLs, allowing attackers to request crafted URLs that use all available memory in Jenkins, potentially leading to out of memory errors.
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Analysis
by VulDB Data Team • 02/14/2021
This vulnerability exists in Jenkins versions up to 2.274 and LTS versions up to 2.263.1 where the graph rendering functionality fails to properly validate and limit the size parameters provided in query strings. The flaw allows attackers to craft malicious URLs that request excessive memory usage through graph rendering operations, potentially exhausting available system resources and causing out of memory conditions. The vulnerability falls under the category of insufficient input validation as defined by CWE-20, where the system does not adequately restrict the size of user-provided parameters that directly influence resource allocation. Attackers can exploit this by manipulating query parameters in graph rendering endpoints to request oversized graph dimensions or data sets that consume all available memory. This type of attack directly maps to the attack pattern described in ATT&CK technique T1499.001 which involves resource exhaustion attacks targeting system memory. The vulnerability represents a critical security risk because it can be exploited by unauthenticated users and does not require any special privileges or access rights. The impact extends beyond simple denial of service as it can potentially cause Jenkins to become unresponsive or crash entirely, disrupting continuous integration and deployment workflows that depend on the system.
The technical implementation of this vulnerability stems from the lack of parameter validation in the graph rendering components of Jenkins. When users request graph visualization through specific URL endpoints, the system accepts size parameters without proper bounds checking or memory allocation limits. This allows attackers to specify arbitrarily large values for parameters that control graph dimensions, data points, or rendering complexity. The absence of input sanitization creates a path where maliciously crafted URLs can cause the Java Virtual Machine to allocate excessive heap memory, leading to OutOfMemoryError exceptions. The vulnerability is particularly dangerous because graph rendering operations are commonly used in Jenkins for build status visualization, performance monitoring, and various dashboard components. Attackers can leverage this weakness by constructing URLs with massive size parameters that force the system to attempt allocating memory that exceeds available system resources. The lack of rate limiting or resource consumption monitoring further compounds the issue, allowing a single request to consume all available memory. This type of memory exhaustion attack can be particularly devastating in environments where Jenkins is running with limited memory allocation or in containerized environments with strict resource constraints.
The operational impact of CVE-2021-21607 extends beyond simple service disruption to potentially compromise entire CI/CD pipelines and development workflows. When exploited successfully, the vulnerability can cause Jenkins to become completely unresponsive, preventing developers from accessing build information, triggering new builds, or monitoring project status. This can result in significant downtime for development teams and potentially block critical deployment processes. Organizations using Jenkins in production environments face increased risk of operational disruption, particularly in scenarios where multiple users might be accessing graph rendering features simultaneously. The vulnerability can also be exploited as part of larger attack campaigns where attackers first establish memory exhaustion conditions before attempting other exploits. From a security perspective, this vulnerability demonstrates the importance of implementing proper input validation and resource limits in web applications, especially those handling user-provided data through API endpoints. The attack surface is particularly broad since graph rendering is a common feature across many Jenkins plugins and core functionalities. System administrators may also face challenges in detecting and mitigating this attack because it typically manifests as a legitimate system resource exhaustion rather than an obvious security breach.
The recommended mitigations for this vulnerability include immediate upgrade to Jenkins versions 2.275 or later for regular releases and LTS versions 2.263.2 or later to address the memory limitation issue. Organizations should also implement proper input validation at the application level by adding size parameter restrictions to graph rendering endpoints and establishing memory usage monitoring for Jenkins processes. Network-level protections can include implementing rate limiting for graph rendering endpoints and configuring web application firewalls to detect and block suspicious parameter combinations. System administrators should consider implementing resource limits and memory constraints for Jenkins processes to prevent complete system exhaustion even if the vulnerability is exploited. Additionally, organizations should conduct regular security assessments of their Jenkins installations to identify similar input validation issues in other components. The mitigation approach aligns with security best practices outlined in OWASP Top 10 and NIST cybersecurity frameworks, particularly focusing on input validation and resource management controls. Regular patch management processes should be implemented to ensure timely updates of Jenkins and related plugins to prevent exploitation of known vulnerabilities. Organizations should also consider implementing automated monitoring solutions that can detect unusual memory consumption patterns and alert administrators to potential exploitation attempts. The vulnerability serves as a reminder of the critical importance of validating all user inputs and implementing proper resource limits in web applications to prevent resource exhaustion attacks.