CVE-2026-103499: IBM WebSphere Liberty DOS Vulnerability

CVE-2026-103499 is a denial of service vulnerability in IBM WebSphere Application Server Liberty caused by uncontrolled resource consumption. Remote attackers can exploit this flaw without authentication. This article covers technical details, affected versions, impact assessment, and mitigation strategies.

CVE-2026-103499 Overview

CVE-2026-103499 is a denial of service vulnerability in IBM WebSphere Application Server Liberty. The flaw affects Liberty versions 17.0.0.3 through 26.0.0.10, as well as IBM WebSphere Application Server 8.5 and 9.0 Liberty editions. A remote unauthenticated attacker can trigger uncontrolled resource consumption, degrading or halting service availability. The weakness is tracked as [CWE-400] Uncontrolled Resource Consumption. IBM published advisory details on its support portal following disclosure.

Critical Impact
Remote unauthenticated attackers can exhaust server resources and cause a denial of service against IBM WebSphere Liberty deployments without any user interaction.

Affected Products

IBM WebSphere Application Server Liberty 17.0.0.3 through 26.0.0.10
IBM WebSphere Application Server 8.5 Liberty
IBM WebSphere Application Server 9.0 Liberty

Discovery Timeline

2026-10-13 - CVE-2026-103499 published to NVD
2026-10-13 - Last updated in NVD database

Technical Details for CVE-2026-103499

Vulnerability Analysis

The vulnerability resides in request-handling logic within IBM WebSphere Application Server Liberty. An attacker reaches the vulnerable code path over the network without authentication or user interaction. By submitting crafted requests, the attacker forces the server to allocate resources without appropriate bounds. Repeated requests exhaust CPU, memory, or thread pools and render the application server unresponsive.

The weakness falls under [CWE-400] Uncontrolled Resource Consumption. Liberty does not enforce sufficient limits on the quantity of resources consumed when processing attacker-supplied input. This permits a single remote endpoint to monopolize server capacity.

IBM has not disclosed the specific protocol component or request type that triggers the condition. Administrators should consult the IBM Support Page for component-level detail.

Root Cause

The root cause is missing or inadequate resource throttling in a server-side handler. When input is received, Liberty allocates work without validating the aggregate cost against a safe ceiling. The condition is reachable before authentication, which widens the exposed attack surface considerably.

Attack Vector

Exploitation requires only network reachability to a vulnerable Liberty endpoint. The attacker sends malicious traffic directly to the application server. No credentials, prior access, or victim interaction are required. The impact is limited to availability; confidentiality and integrity are not affected. The EPSS score is 0.404% with a percentile of approximately 33, indicating low current exploitation prediction.

No verified public exploit code is available. See the IBM Support Page for authoritative technical details.

Detection Methods for CVE-2026-103499

Indicators of Compromise

Sustained spikes in Liberty JVM heap usage, garbage collection activity, or thread pool saturation without a corresponding business workload increase.
Elevated connection counts from a small number of source IPs to Liberty HTTP, HTTPS, or management endpoints.
Liberty messages.log entries indicating request timeouts, thread hangs, or rejected work.

Detection Strategies

Baseline normal request volume per source and alert on statistical anomalies against Liberty listener ports.
Correlate network flow telemetry with JVM performance metrics to identify resource-exhaustion patterns.
Monitor WebSphere FFDC (First Failure Data Capture) output for recurring resource allocation failures.

Monitoring Recommendations

Instrument Liberty with JMX or Prometheus exporters to capture thread pool, heap, and session metrics in real time.
Forward Liberty access and server logs to a centralized analytics platform for correlation with network telemetry.
Alert on repeated HTTP 503 responses or connection resets originating from the Liberty front end.

How to Mitigate CVE-2026-103499

Immediate Actions Required

Apply the IBM-provided fix for CVE-2026-103499 as documented on the IBM Support Page.
Inventory all WebSphere Application Server Liberty instances and confirm versions against the affected range 17.0.0.3 through 26.0.0.10, plus 8.5 and 9.0 Liberty.
Restrict exposure of Liberty endpoints to trusted networks until patches are deployed.

Patch Information

IBM has published remediation guidance on its support portal. Review the IBM Support Page for the specific interim fix, fix pack, or configuration update applicable to your deployed Liberty version. Validate the patch in a non-production environment before rolling out to production.

Workarounds

Place a reverse proxy or Web Application Firewall in front of Liberty to enforce request rate limits and connection quotas per source IP.
Tune Liberty executor thread pool, HTTP endpoint maxKeepAliveRequests, and connection timeout values to constrain resource consumption.
Block or throttle unauthenticated traffic to Liberty endpoints at the network perimeter where business requirements permit.

bash

# Example Liberty server.xml hardening for connection and request limits
<httpEndpoint id="defaultHttpEndpoint"
              host="*"
              httpPort="9080"
              httpsPort="9443">
    <tcpOptions soReuseAddr="true" />
    <httpOptions maxKeepAliveRequests="100"
                 persistTimeout="30s"
                 readTimeout="30s"
                 writeTimeout="30s" />
</httpEndpoint>

<executor name="LargeThreadPool"
          coreThreads="25"
          maxThreads="100" />