CVE-2025-36116: IBM Db2 Mirror for i XSS Vulnerability

CVE-2025-36116 Overview

CVE-2025-36116 is a cross-site WebSocket hijacking (CSWSH) vulnerability affecting the IBM Db2 Mirror for i graphical user interface. The flaw exists in versions 7.4, 7.5, and 7.6 of the product. An unauthenticated remote attacker can craft a malicious request that sniffs an existing authenticated WebSocket connection. Once the connection is hijacked, the attacker can issue operations through the victim's session that they would otherwise be denied. The vulnerability is tracked under CWE-1385: Missing Origin Validation in WebSockets.

Critical Impact
An attacker who successfully lures an authenticated Db2 Mirror for i administrator to a malicious page can perform administrative actions on the mirror configuration through the hijacked WebSocket channel.

Affected Products

IBM Db2 Mirror for i 7.4
IBM Db2 Mirror for i 7.5
IBM Db2 Mirror for i 7.6

Discovery Timeline

2025-07-23 - CVE-2025-36116 published to the National Vulnerability Database
2026-06-17 - Last updated in the NVD database

Technical Details for CVE-2025-36116

Vulnerability Analysis

The Db2 Mirror for i GUI uses WebSocket connections to stream data between the administrator's browser and the server. The server accepts WebSocket upgrade requests without validating the Origin header against an allowlist. This omission is the defining characteristic of CWE-1385 and enables cross-site WebSocket hijacking.

When a victim with an active Db2 Mirror session visits an attacker-controlled page, the browser transmits session cookies with the WebSocket handshake. The Db2 Mirror server treats the resulting connection as legitimate and binds it to the victim's authenticated session. The attacker's JavaScript then reads server responses and issues arbitrary commands that inherit the victim's privileges.

An EPSS score of 0.159% indicates a low probability of exploitation activity in the near term, but the impact of a successful hijack scales with the privileges of the targeted user.

Root Cause

The root cause is missing origin validation during the WebSocket upgrade handshake. The server relies on cookie-based session authentication without enforcing same-origin or CSRF token checks on the initial GET request that upgrades to the ws:// or wss:// protocol.

Attack Vector

Exploitation requires the victim to visit a malicious web page while holding an authenticated Db2 Mirror GUI session. The attacker's page opens a WebSocket connection to the Db2 Mirror server URL. Because browsers do not enforce the same-origin policy on WebSocket handshakes by default, the connection succeeds and streams messages back to the attacker's script. The attacker can then send crafted messages to trigger operations such as configuration changes or data queries that the malicious origin should not be permitted to perform.

No verified public proof-of-concept code was available at the time of writing. Refer to the IBM Support advisory for vendor technical details.

Detection Methods for CVE-2025-36116

Indicators of Compromise

WebSocket handshake requests to the Db2 Mirror GUI where the Origin header does not match the expected internal management host
Unexpected configuration or replication operations initiated shortly after a user browsed external sites
WebSocket sessions originating from user agents or referrers that do not match approved administrative browsers

Detection Strategies

Inspect web server and reverse proxy logs for Upgrade: websocket requests with foreign Origin values and alert on mismatches
Correlate Db2 Mirror administrative actions with the source IP and browser session that initiated them to spot anomalies
Deploy a web application firewall rule that blocks WebSocket handshakes lacking a trusted Origin header

Monitoring Recommendations

Enable verbose audit logging on the Db2 Mirror GUI service and forward events to a centralized SIEM
Monitor for administrative operations performed outside of standard change windows or from unusual client fingerprints
Track authentication and session lifetime metrics to identify sessions used from multiple concurrent origins

How to Mitigate CVE-2025-36116

Immediate Actions Required

Apply the IBM-provided fix documented in the IBM Support advisory for Db2 Mirror for i 7.4, 7.5, and 7.6
Restrict network access to the Db2 Mirror GUI so that only trusted management workstations can reach the service
Require administrators to use a dedicated browser profile for Db2 Mirror sessions and to log out when finished

Patch Information

IBM has published remediation guidance and PTF references on the IBM Support page for CVE-2025-36116. Administrators should identify the appropriate group PTF level for their IBM i release and apply the vendor-recommended fix.

Workarounds

Place the Db2 Mirror GUI behind a reverse proxy that enforces strict Origin header validation on WebSocket upgrades
Segment the management network so that administrator browsers cannot simultaneously reach both the Db2 Mirror GUI and untrusted internet content
Shorten session timeouts on the Db2 Mirror GUI to reduce the window in which a hijacked session remains valid

bash

# Example reverse proxy Origin validation for WebSocket upgrades (nginx)
map $http_origin $origin_ok {
    default 0;
    "https://db2mirror.internal.example.com" 1;
}

server {
    listen 443 ssl;
    server_name db2mirror.internal.example.com;

    location / {
        if ($origin_ok = 0) { return 403; }
        proxy_pass https://db2mirror_backend;
        proxy_http_version 1.1;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection "upgrade";
        proxy_set_header Host $host;
    }
}