CVE-2024-3884: Undertow Denial of Service Vulnerability

CVE-2024-3884 Overview

A flaw in Undertow allows unauthenticated remote attackers to trigger denial of service conditions through malformed form data parsing. When the server processes large application/x-www-form-urlencoded payloads using the FormEncodedDataDefinition.doParse(StreamSourceChannel) method, the parser consumes excessive heap memory and triggers an OutOfMemoryError. The condition exhausts JVM heap resources and forces affected web servers offline. Undertow is the embedded web server used in Red Hat JBoss Enterprise Application Platform and WildFly, making this issue relevant to enterprise Java application stacks. The vulnerability is tracked under [CWE-20] (Improper Input Validation).

Critical Impact

Unauthenticated attackers can crash Undertow-based application servers remotely by submitting oversized URL-encoded form payloads, disrupting availability of business-critical Java workloads.

Affected Products

• Red Hat JBoss Enterprise Application Platform (multiple versions, per Red Hat advisories)
• Red Hat build of Apache Camel and Quarkus distributions bundling Undertow
• Undertow web server (upstream component shipped within affected Red Hat products)

Discovery Timeline

• 2025-12-03 - CVE-2024-3884 published to the National Vulnerability Database
• 2026-04-15 - Last updated in NVD database

Technical Details for CVE-2024-3884

Vulnerability Analysis

The defect resides in Undertow's form parsing subsystem. The FormEncodedDataDefinition.doParse(StreamSourceChannel) method reads inbound form data from the channel and accumulates parsed name/value pairs in memory. The parser does not enforce a hard upper bound on the cumulative size of buffered form content before allocation. An attacker who submits a single request with an extremely large URL-encoded body forces the JVM to allocate buffers proportional to the payload size. Once heap capacity is exceeded, the JVM throws OutOfMemoryError, which terminates request threads and can destabilize the entire application server process. Because the attack requires only a network-reachable HTTP endpoint that accepts form submissions, it scales trivially against exposed Undertow deployments.

Root Cause

The root cause is improper input validation [CWE-20] in the form data parser. The doParse method trusts the size of the inbound stream and lacks a configurable cap on parsed form content length. Memory allocation grows linearly with attacker-controlled input.

Attack Vector

Exploitation is network-based, requires no authentication, and needs no user interaction. An attacker sends an HTTP POST request with Content-Type: application/x-www-form-urlencoded containing a very large body to any endpoint backed by Undertow's form parser. Repeated requests amplify resource exhaustion and accelerate process termination. Refer to the Red Hat CVE-2024-3884 Details and Red Hat Bug Report #2275287 for vendor analysis.

Detection Methods for CVE-2024-3884

Indicators of Compromise

• Repeated java.lang.OutOfMemoryError: Java heap space entries in Undertow, WildFly, or JBoss EAP server logs correlated with inbound HTTP traffic.
• Abnormally large Content-Length values on POST requests with Content-Type: application/x-www-form-urlencoded to application endpoints.
• Sudden JVM process termination or container restarts on Undertow-based workloads without preceding application errors.

Detection Strategies

• Inspect web access logs for POST requests with oversized bodies targeting form-handling routes, particularly from a single source address.
• Correlate JVM heap usage spikes with HTTP request volume to identify resource exhaustion patterns tied to form submissions.
• Apply Web Application Firewall (WAF) rules that flag URL-encoded request bodies exceeding a defined size threshold appropriate for the application.

Monitoring Recommendations

• Enable JVM garbage collection and heap monitoring on Undertow workloads and alert on sustained heap pressure above 85 percent.
• Track HTTP 5xx error rates and process restart counts on application servers to detect availability impact early.
• Forward application server and reverse proxy logs to a centralized analytics platform for cross-tier correlation of DoS patterns.

How to Mitigate CVE-2024-3884

Immediate Actions Required

• Apply the Red Hat security updates published for affected JBoss EAP, WildFly, and downstream products. Begin with the latest applicable RHSA, such as RHSA-2026:6011 and RHSA-2026:6012.
• Inventory all internal and external applications running on Undertow and prioritize internet-facing endpoints that accept form submissions.
• Configure upstream reverse proxies or load balancers to enforce a maximum request body size for application/x-www-form-urlencoded traffic.

Patch Information

Red Hat has issued multiple errata addressing CVE-2024-3884 across product lines, including RHSA-2026:0383, RHSA-2026:0384, RHSA-2026:0386, RHSA-2026:3889, RHSA-2026:3891, RHSA-2026:3892, RHSA-2026:4915, RHSA-2026:4916, RHSA-2026:4917, and RHSA-2026:4924. Administrators should consult the Red Hat CVE-2024-3884 Details page to map their specific product version to the correct erratum.

Workarounds

• Place a reverse proxy such as NGINX or HAProxy in front of Undertow and enforce a strict client_max_body_size or equivalent limit on POST requests.
• Restrict access to form-handling endpoints through network segmentation, authentication requirements, or rate limiting where the application design allows.
• Configure JVM heap limits and container memory cgroups so that an OutOfMemoryError triggers a controlled restart rather than prolonged service degradation.

# Example NGINX reverse proxy mitigation: cap form body size in front of Undertow
http {
    client_max_body_size 1m;

    server {
        listen 443 ssl;
        server_name app.example.com;

        location / {
            proxy_pass http://undertow_backend;
            proxy_set_header Host $host;
            proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        }
    }
}