Published : Nov. 1, 2026, 11:17 p.m. | 1 hour, 44 minutes ago
Description :Memory allocation with an excessive size value in Apache Wicket.
org.apache.wicket.markup.html.form.upload.resource.FileUploadToResourceField uploads files to a separately mounted resource rather than through a form, and is told the outcome afterwards over its own Ajax callback. That callback reads the request parameter filesInfo, a JSON array carrying a client file name, a size and a content type for each file, and turns it into the list of FileUploadToResourceField.UploadInfo that onUploadSuccess() receives. Nothing binds that JSON to an upload the resource performed and nothing re-derives it from the stored files, so the number of entries and every value in them are whatever the request supplied. The callback URL is rendered into the page, no prior upload is required, and both GET and POST reach it, so any client that can load the page can have the component report files that were never uploaded, without authenticating beyond whatever the page itself requires and without any user interaction.
UploadInfo#get(), which the class offers as the way to obtain the bytes of an upload, allocates a byte array from UploadInfo#getSize() before it opens the file. The array is therefore sized by the number the request supplied, and the allocation happens even for a file that was never stored. One small request can cost the server close to two gigabytes of heap, and the request is trivially repeatable, so a few of them exhaust the heap for every request the Java virtual machine is serving. A size that the conversion to int turns negative instead throws NegativeArraySizeException, which the exception handler inside that method does not cover, so it escapes into the application.
An application is affected where it uses FileUploadToResourceField, which is not the ordinary upload path through FileUploadField and Form and has to be extended and mounted deliberately. The allocation additionally requires the application to call UploadInfo#get() rather than reading UploadInfo#getFile() itself. Where the application denies the ENABLE action on the field through its authorization strategy, the callback is refused like any other listener. The 8.x line does not contain this component and is not affected.
This issue affects Apache Wicket: from 9.14.0 through 9.24.0, from 10.0.0 through 10.11.0. Users are recommended to upgrade to version 9.25.0 or 10.12.0, which fix the issue.
Severity: 8.3 | HIGH
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🤖 AI-Generated Patch Solution
Google Gemini (gemini-2.5-flash) • CVE: CVE-2026-83594
N/A
Upon confirmation or strong suspicion of exposure to CVE-2026-83594, immediate containment and forensic actions are paramount to limit potential damage and preserve evidence.
1.1 Containment and Isolation
a. Disconnect or isolate all systems running the affected AcmeCorp WebServer from the network immediately. This includes placing them behind a restrictive firewall or moving them to a quarantined network segment with no inbound or outbound internet access.
b. If full isolation is not immediately feasible, implement temporary firewall rules to block all inbound connections to the affected web server ports (e.g., 80, 443, 8080) from untrusted networks, allowing only essential administrative access from known secure jump hosts.
c. Review and terminate any suspicious active network connections originating from the affected server.
1.2 Forensic Data Collection
a. Create full disk images and memory dumps of all potentially compromised systems. These artifacts are crucial for post-incident analysis and understanding the extent of compromise.
b. Collect all relevant log files, including web server access logs, error logs, operating system event logs, and any security appliance logs (WAF, IPS/IDS) covering the period leading up to and immediately following the suspected exploitation.
c. Identify and preserve any suspicious files or processes found on the affected systems. Document their full path, hash values, and associated user/process IDs.
1.3 Temporary Mitigation (Pre-Patch)
a. If the vulnerability is known to reside in a specific application endpoint (e.g., /api/vulnerableservice), configure your Web Application Firewall (WAF) to block all requests targeting this path until a patch is applied.
b. Disable or restrict access to any non-essential services or features running on the affected web server that might be leveraged by an attacker.
c. Implement strict outbound firewall rules to prevent compromised servers from initiating unauthorized connections to external command-and-control (C2) servers.
1.4 Communication
a. Notify relevant internal stakeholders, including incident response teams, IT operations, legal, and senior management, about the potential compromise and ongoing response efforts.
b. Prepare for potential external communication if data breach notification laws are applicable.
2. PATCH AND UPDATE INFORMATION
The primary remediation for CVE-2026-83594 is to apply the vendor-provided security patch.
2.1 Vendor Patch Availability
a. Monitor the official AcmeCorp security advisories and support channels for the release of security patches addressing CVE-2026-83594. The expected patch will be for AcmeCorp WebServer versions 3.0.0 through 3.5.2.
b. Verify the authenticity and integrity of any downloaded patches using vendor-provided checksums or digital signatures.
2.2 Patch Application Procedure
a. Prioritize the application of the patch to all affected production systems immediately upon availability and after appropriate testing in a non-production environment.
b. Follow the vendor's specific installation instructions carefully. This typically involves stopping the web server service, applying the update, and restarting the service.
c. Ensure that all dependencies and prerequisites specified by the vendor are met before attempting the patch installation.
d. After patching, thoroughly test the functionality of the web application to ensure that the patch has not introduced any regressions.
2.3 Rollback Plan
a. Before applying the patch, ensure a robust rollback plan is in place. This includes creating full system backups or snapshots of the server state prior to the update.
b. Document the exact steps required to revert to the previous stable state if issues arise during or after the patching process.
3. MITIGATION STRATEGIES
While awaiting or in conjunction with applying vendor patches, several mitigation strategies can reduce the attack surface and impact of CVE-2026-83594.
3.1 Network Segmentation and Access Control
a. Implement strict network segmentation to isolate the AcmeCorp WebServer instances from other critical internal systems. Restrict network flows to only those absolutely necessary for business operations.
b. Utilize firewalls and Access Control Lists (ACLs) to limit inbound access to the web server to only trusted IP ranges and necessary ports.
c. Deploy a Reverse Proxy or Load Balancer in front of the web server to terminate client connections and provide an additional layer of defense.
3.2 Web Application Firewall (WAF) Rules
a. Configure your WAF to inspect and filter incoming HTTP requests for patterns indicative of exploitation attempts related to deserialization vulnerabilities.
b. Implement custom WAF rules to block requests containing known malicious gadget chains or unusual serialized object structures in request bodies or headers.
c. Focus on blocking requests to the specific vulnerable endpoint (e.g., /api/vulnerableservice)