CVE-2023-20883: VMware Spring Boot DoS Vulnerability

CVE-2023-20883 Overview

CVE-2023-20883 is a denial-of-service (DoS) vulnerability affecting VMware Spring Boot when used together with Spring MVC and a reverse proxy cache. This vulnerability allows unauthenticated remote attackers to cause service disruption by exploiting how the application handles cached responses through the reverse proxy, potentially rendering the application unavailable to legitimate users.

Critical Impact

Unauthenticated attackers can remotely trigger denial-of-service conditions against Spring Boot applications using Spring MVC with reverse proxy caching, causing widespread service disruption without requiring any credentials or user interaction.

Affected Products

• VMware Spring Boot versions 3.0.0 - 3.0.6
• VMware Spring Boot versions 2.7.0 - 2.7.11
• VMware Spring Boot versions 2.6.0 - 2.6.14
• VMware Spring Boot versions 2.5.0 - 2.5.14 and older unsupported versions

Discovery Timeline

• May 26, 2023 - CVE-2023-20883 published to NVD
• January 16, 2025 - Last updated in NVD database

Technical Details for CVE-2023-20883

Vulnerability Analysis

This vulnerability is classified under CWE-400 (Uncontrolled Resource Consumption), indicating that the flaw allows attackers to exhaust system resources. The attack is network-based and can be executed remotely without authentication or user interaction. The vulnerability specifically manifests in deployments where Spring MVC is configured behind a reverse proxy cache, creating a scenario where malicious requests can manipulate cached responses to consume excessive resources or cause the application to become unresponsive.

The exploitation requires a specific architectural configuration: Spring Boot applications running Spring MVC behind a reverse proxy that implements response caching. When this configuration is present, attackers can craft requests that abuse the caching mechanism to trigger denial-of-service conditions.

Root Cause

The root cause lies in improper handling of requests when Spring MVC operates in conjunction with reverse proxy caching infrastructure. The vulnerability stems from how cached responses are processed and served, allowing attackers to manipulate the cache behavior in ways that lead to resource exhaustion or service unavailability. This represents an uncontrolled resource consumption issue where the application fails to properly limit or manage resources when handling certain request patterns through the proxy cache layer.

Attack Vector

The attack vector is network-based, allowing remote exploitation without requiring authentication or user interaction. Attackers can target Spring Boot applications by sending specially crafted HTTP requests that exploit the interaction between Spring MVC and the reverse proxy cache. The attack does not require local access to the system, making it exploitable from anywhere on the network that can reach the vulnerable application endpoint.

The vulnerability affects only the availability aspect of the CIA triad - no confidentiality or integrity impacts have been identified. This means attackers cannot use this vulnerability to steal data or modify application behavior, but they can effectively take the service offline for legitimate users.

Detection Methods for CVE-2023-20883

Indicators of Compromise

• Unusual spikes in HTTP request rates targeting Spring MVC endpoints
• Increased memory or CPU consumption on Spring Boot application servers
• Reverse proxy cache showing abnormal hit/miss ratios or unexpected cache invalidation patterns
• Application logs indicating resource exhaustion or timeout errors

Detection Strategies

• Monitor application performance metrics for sudden degradation in response times or throughput
• Implement rate limiting and anomaly detection on incoming HTTP requests at the reverse proxy layer
• Review Spring Boot application logs for patterns indicating denial-of-service attempts
• Configure alerting on JVM metrics showing memory pressure or thread pool exhaustion

Monitoring Recommendations

• Deploy application performance monitoring (APM) solutions to track Spring Boot application health
• Establish baseline metrics for normal request patterns and alert on significant deviations
• Monitor reverse proxy access logs for suspicious request patterns or high-volume traffic from single sources
• Implement distributed tracing to identify request patterns that correlate with performance degradation

How to Mitigate CVE-2023-20883

Immediate Actions Required

• Upgrade Spring Boot to patched versions: 3.0.7 or later for 3.x branch, 2.7.12 or later for 2.7.x branch, 2.6.15 or later for 2.6.x branch
• If immediate patching is not possible, review and restrict reverse proxy cache configurations
• Implement rate limiting at the reverse proxy or load balancer level to mitigate potential DoS attempts
• Monitor affected applications for signs of exploitation while planning upgrade windows

Patch Information

VMware has released security patches addressing this vulnerability across all supported Spring Boot version branches. The official security advisory is available at the Spring Security CVE-2023-20883 Advisory. Additional vendor information is available from NetApp Security Advisory NTAP-20230703-0008 for NetApp products that incorporate Spring Boot.

Users should upgrade to the following minimum versions:

• Spring Boot 3.x: Upgrade to 3.0.7 or later
• Spring Boot 2.7.x: Upgrade to 2.7.12 or later
• Spring Boot 2.6.x: Upgrade to 2.6.15 or later
• Spring Boot 2.5.x and earlier: Upgrade to a supported branch as these versions are no longer maintained

Workarounds

• Disable or reconfigure reverse proxy caching for Spring MVC endpoints until patches can be applied
• Implement Web Application Firewall (WAF) rules to filter potentially malicious request patterns
• Configure connection limits and request timeouts at the reverse proxy level
• Consider temporary removal of caching layers from the request path for critical applications

# Example: Configure rate limiting in nginx reverse proxy
# Add to nginx.conf or server block configuration
limit_req_zone $binary_remote_addr zone=springboot_limit:10m rate=100r/s;

location / {
    limit_req zone=springboot_limit burst=200 nodelay;
    proxy_pass http://spring_boot_backend;
    proxy_connect_timeout 60s;
    proxy_read_timeout 60s;
}