CVE-2025-27901: IBM Db2 Recovery Expert XSS Vulnerability

CVE-2025-27901 Overview

CVE-2025-27901 affects IBM Db2 Recovery Expert for Linux, UNIX and Windows version 5.5 Interim Fix 002. The vulnerability stems from improper validation of input within HTTP Host headers, classified as [CWE-644] Improper Neutralization of HTTP Headers for Scripting Syntax. Attackers can leverage this flaw to conduct cross-site scripting, web cache poisoning, and session hijacking attacks against the affected application. The issue is exploitable over the network without authentication or user interaction.

Critical Impact
Unauthenticated remote attackers can inject malicious content into HTTP Host headers, enabling XSS, cache poisoning, and session hijacking against users of IBM Db2 Recovery Expert.

Affected Products

IBM Db2 Recovery Expert for LUW 5.5 Interim Fix 002 (Linux)
IBM Db2 Recovery Expert for LUW 5.5 Interim Fix 002 (UNIX)
IBM Db2 Recovery Expert for LUW 5.5 Interim Fix 002 (Windows)

Discovery Timeline

2026-02-17 - CVE-2025-27901 published to NVD
2026-02-25 - Last updated in NVD database

Technical Details for CVE-2025-27901

Vulnerability Analysis

IBM Db2 Recovery Expert for LUW exposes a web management interface that processes HTTP requests from administrators. The application fails to properly validate or sanitize the value supplied in the HTTP Host header before reflecting or using that value in server-side logic and responses. An attacker who can send crafted HTTP requests to the application can manipulate the Host header to influence generated URLs, redirects, and cached responses.

This class of weakness allows three primary attack outcomes. First, injected script content in headers may be reflected into responses, producing cross-site scripting against authenticated users. Second, poisoned Host values can cause upstream caches or reverse proxies to store attacker-controlled responses and serve them to other users. Third, manipulated absolute URLs in password reset flows or session-bound responses can be redirected to attacker-controlled hosts, enabling session hijacking.

Root Cause

The root cause is missing or insufficient validation of the Host request header before its value is consumed by the application. The framework trusts the client-supplied header value rather than constraining it to an allowlist of expected hostnames or values derived from server configuration.

Attack Vector

Exploitation requires only network reachability to the Db2 Recovery Expert web interface. No authentication or user interaction is needed to send a crafted request. The attacker submits an HTTP request with a malicious Host header value, such as a host containing script payloads or a domain controlled by the attacker. Downstream rendering, caching, or URL-generation logic then produces the malicious effect.

No public proof-of-concept or exploitation activity has been documented for CVE-2025-27901. The vulnerability is not listed on the CISA Known Exploited Vulnerabilities catalog.

Detection Methods for CVE-2025-27901

Indicators of Compromise

HTTP requests to Db2 Recovery Expert endpoints with Host header values that do not match the configured server hostname or load balancer FQDN.
Host header values containing script tags, HTML entities, embedded CRLF sequences, or unexpected port and path syntax.
Web cache entries keyed by anomalous host values, or outbound links in application responses pointing to unknown external domains.

Detection Strategies

Parse web server and reverse proxy access logs for requests where the Host header deviates from an allowlist of approved hostnames serving Db2 Recovery Expert.
Inspect responses for reflected Host values appearing inside HTML, Location headers, or absolute URLs generated by the application.
Correlate authentication events with subsequent redirects to external domains to surface potential session hijacking via header injection.

Monitoring Recommendations

Enable verbose HTTP logging on the Db2 Recovery Expert host and forward logs to a centralized analytics platform for retention and search.
Alert on repeated requests from a single source containing varied or malformed Host header values, which suggests probing.
Monitor cache infrastructure for entries whose cache key includes an unexpected host component.

How to Mitigate CVE-2025-27901

Immediate Actions Required

Apply the remediation referenced in the IBM Support advisory for CVE-2025-27901 as soon as it is available for your platform.
Restrict network access to the Db2 Recovery Expert web interface to trusted administrative networks using firewall or segmentation controls.
Place the application behind a reverse proxy configured to enforce a strict Host header allowlist and reject non-conforming requests.

Patch Information

IBM has published guidance for CVE-2025-27901 on its support portal. Review the IBM Support Page for the authoritative fix instructions, applicable interim fix levels, and platform-specific download links for Linux, UNIX, and Windows builds of Db2 Recovery Expert 5.5.

Workarounds

Configure the upstream web server or proxy to validate the Host header against the canonical FQDN and reject requests containing unexpected values.
Disable or limit any application features that generate absolute URLs from the Host header until the patch is applied.
Require authenticated VPN access to reach the management interface, reducing exposure to unauthenticated attackers.

bash

# Example nginx reverse proxy rule enforcing a Host header allowlist
server {
    listen 443 ssl;
    server_name recovery.example.com;

    if ($host !~* ^(recovery\.example\.com)$ ) {
        return 400;
    }

    location / {
        proxy_set_header Host $host;
        proxy_pass http://db2_recovery_backend;
    }
}