CVE-2026-57819: Apache CXF DoS Vulnerability

CVE-2026-57819 Overview

CVE-2026-57819 is a denial of service vulnerability in Apache CXF affecting the JAX-RS message processing subsystem. Apache CXF exposes a maxFormParameterCount configuration option to cap the number of form parameters accepted in a request. No default limit was enforced, allowing attackers to submit requests containing very large numbers of form parameters. Processing these requests consumes excessive server resources and can exhaust CPU and memory. The issue is tracked under CWE-400 (Uncontrolled Resource Consumption). Fixed versions ship with a default limit of 500 parameters.

Critical Impact
Unauthenticated remote attackers can trigger denial of service against Apache CXF JAX-RS endpoints by submitting requests containing an unbounded number of form parameters.

Affected Products

Apache CXF versions prior to 4.2.3 (4.2.x branch)
Apache CXF versions prior to 4.1.8 (4.1.x branch)
Apache CXF versions prior to 3.6.12 (3.6.x branch)

Discovery Timeline

2026-08-06 - CVE-2026-57819 published to NVD
2026-08-06 - Last updated in NVD database

Technical Details for CVE-2026-57819

Vulnerability Analysis

Apache CXF is an open source services framework that supports JAX-RS and JAX-WS APIs. The framework parses form-encoded request bodies (application/x-www-form-urlencoded) into parameter maps for JAX-RS resource methods. The maxFormParameterCount configuration option exists to bound the number of parameters accepted per request. Prior to the fixed releases, this option had no default value, so deployments that did not explicitly configure it accepted an unlimited count.

An attacker can send a single HTTP request with tens or hundreds of thousands of form key-value pairs. The parser allocates map entries and performs work for each parameter, driving CPU utilization and heap consumption upward. Repeated requests amplify the effect and can make the service unresponsive to legitimate traffic.

Root Cause

The root cause is a missing safe default for a resource-limiting configuration parameter. The framework relied on operators to opt in to the limit rather than enforcing a conservative ceiling out of the box. This falls under Uncontrolled Resource Consumption [CWE-400].

Attack Vector

Exploitation requires the ability to send HTTP requests to a JAX-RS endpoint that consumes form-encoded input. No authentication is inherently required if the target endpoint accepts unauthenticated requests. The attacker crafts an oversized form body and issues it against the vulnerable endpoint. See the Apache Security Advisory for vendor-supplied detail.

Detection Methods for CVE-2026-57819

Indicators of Compromise

HTTP POST or PUT requests with Content-Type: application/x-www-form-urlencoded and abnormally large Content-Length values reaching JAX-RS endpoints.
Request bodies containing thousands of key=value& pairs from a single source IP or a small set of sources.
Java process spikes in CPU and heap usage correlated with inbound requests to Apache CXF services.

Detection Strategies

Inspect web server and reverse proxy logs for requests with unusually large form payloads directed at CXF-hosted paths.
Enable metrics on JVM heap, garbage collection frequency, and request latency for services built on Apache CXF.
Add WAF rules that count & separators in form bodies and flag requests exceeding a chosen threshold.

Monitoring Recommendations

Alert on sustained increases in 5xx response rates from JAX-RS endpoints, which often accompany resource exhaustion.
Track thread pool saturation and request queue depth on the application server hosting Apache CXF.
Correlate spikes with source IP reputation feeds to identify low-and-slow abuse patterns.

How to Mitigate CVE-2026-57819

Immediate Actions Required

Upgrade Apache CXF to version 4.2.3, 4.1.8, or 3.6.12 depending on the branch in use.
Where an immediate upgrade is not possible, set maxFormParameterCount explicitly to a low value such as 500.
Enforce request body size limits at the reverse proxy or load balancer in front of CXF services.
Rate limit unauthenticated form submissions to JAX-RS endpoints.

Patch Information

The Apache CXF project fixed the issue by applying a default maxFormParameterCount of 500 in versions 4.2.3, 4.1.8, and 3.6.12. Consult the Apache Security Advisory for the authoritative fix details and release notes.

Workarounds

Configure maxFormParameterCount on the JAX-RS server or bus to a conservative value.
Reject requests larger than the expected form payload size at the perimeter using an HTTP proxy or WAF.
Restrict access to internal JAX-RS endpoints using network segmentation and authentication where feasible.

bash

# Configuration example: set maxFormParameterCount on a JAX-RS server bean
# Apply in your Spring or Blueprint configuration for Apache CXF
# <jaxrs:server address="/api">
#   <jaxrs:properties>
#     <entry key="maxFormParameterCount" value="500"/>
#   </jaxrs:properties>
# </jaxrs:server>