CVE-2026-50645: Apache CXF DOS Vulnerability

CVE-2026-50645 Overview

CVE-2026-50645 is a denial of service vulnerability in Apache CXF, an open source services framework for building web services using protocols such as SOAP, REST, and JAX-WS. The flaw stems from the absence of any limit on the number of attachment headers permitted within a message during deserialization. A remote, unauthenticated attacker can submit a crafted message containing an excessive number of attachment headers, causing uncontrolled resource consumption on the target server. The issue is tracked under CWE-400 (Uncontrolled Resource Consumption). Apache has remediated the issue in versions 4.2.2 and 4.1.7 by introducing a default cap of 500 attachments per message.

Critical Impact
Remote, unauthenticated attackers can trigger denial of service against Apache CXF services by sending messages with unbounded attachment headers, exhausting memory and CPU resources.

Affected Products

Apache CXF versions prior to 4.2.2 on the 4.2.x branch
Apache CXF versions prior to 4.1.7 on the 4.1.x branch
Any application or service framework embedding vulnerable Apache CXF releases

Discovery Timeline

2026-06-12 - CVE-2026-50645 published to NVD
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2026-50645

Vulnerability Analysis

Apache CXF processes multipart messages that may contain attachments, each accompanied by its own set of MIME headers. During message deserialization, CXF iterates over and stores these attachment headers without enforcing an upper bound on their count. An attacker who can reach any CXF endpoint accepting multipart input can submit a single request containing an arbitrary number of attachment parts. Each part forces the server to allocate memory structures to parse and retain header data. The cumulative allocation consumes heap memory, threads, and CPU cycles, ultimately rendering the service unresponsive to legitimate clients.

The vulnerability is exploitable over the network without authentication or user interaction. Impact is limited to availability, as no confidentiality or integrity boundaries are crossed. The EPSS score is 0.616% with a percentile of 44.811 as of 2026-06-18, indicating moderate near-term exploitation likelihood.

Root Cause

The root cause is the lack of an enforced maximum on attachment headers within the CXF attachment deserialization path. Without a ceiling, parsing logic continues to allocate resources for every header encountered in the incoming stream. This design omission falls under CWE-400, uncontrolled resource consumption.

Attack Vector

An attacker delivers a crafted multipart MIME message to any reachable CXF endpoint that accepts attachments. The message contains a large volume of attachment parts or headers. CXF accepts and begins processing each, exhausting JVM heap space or thread capacity. Repeating the request from a single client or a small botnet can sustain the denial of service condition. No credentials, prior access, or user interaction are required.

For technical specifics, refer to the Apache Mailing List Thread and the OpenWall OSS Security Update.

Detection Methods for CVE-2026-50645

Indicators of Compromise

Inbound HTTP or SOAP requests with multipart MIME bodies containing hundreds or thousands of attachment parts
Sudden spikes in JVM heap utilization, garbage collection activity, or thread counts on CXF service hosts
HTTP 5xx errors, request timeouts, or service unavailability correlated with large multipart payloads
Repeated requests from the same source IP delivering oversized multipart messages

Detection Strategies

Inspect web application firewall and reverse proxy logs for multipart requests with abnormally high Content-Length values or part counts
Enable verbose logging on CXF interceptors to record attachment counts per request and alert on outliers
Correlate application performance monitoring metrics with request payload characteristics to identify resource-exhaustion patterns

Monitoring Recommendations

Establish baselines for normal attachment counts and payload sizes across CXF endpoints
Forward CXF and application server logs to a centralized analytics platform for anomaly detection on request size and processing duration
Alert security operations when JVM heap pressure, request latency, or 5xx error rates exceed defined thresholds on services exposing CXF

How to Mitigate CVE-2026-50645

Immediate Actions Required

Upgrade Apache CXF to version 4.2.2 or 4.1.7 as published by the Apache Software Foundation
Inventory all internal and customer-facing applications embedding CXF and confirm the dependency version in build manifests
Place a web application firewall or API gateway in front of CXF services to enforce request size and part-count limits until patches are deployed

Patch Information

The Apache CXF project resolved CVE-2026-50645 by introducing a default maximum of 500 attachments per message. Users running 4.2.x must upgrade to 4.2.2, and users running 4.1.x must upgrade to 4.1.7. See the Apache Mailing List Thread for the official advisory.

Workarounds

Configure reverse proxies or API gateways to reject multipart requests exceeding a reasonable size or part-count threshold
Restrict access to CXF endpoints to authenticated, trusted clients where business requirements allow
Apply rate limiting and connection throttling to limit the volume of multipart requests any single client can issue
Monitor JVM resource usage and configure automatic restarts or circuit breakers to recover from resource exhaustion events

bash

# Example: enforce a 10MB maximum multipart request size at an Nginx reverse proxy
http {
    client_max_body_size 10m;
    client_body_buffer_size 128k;

    server {
        location /services/ {
            proxy_pass http://cxf_backend;
            proxy_read_timeout 30s;
        }
    }
}