CVE-2026-10837: X-Forwarded-Host Open Redirect Vulnerability

CVE-2026-10837 Overview

CVE-2026-10837 is an open redirection vulnerability caused by insufficient validation of the X-Forwarded-Host HTTP header in a password manager application. Attackers can craft manipulated links that redirect victims to attacker-controlled domains when opened. The flaw maps to CWE-601: URL Redirection to Untrusted Site and enables phishing and deception attacks. Exploitation requires user interaction, typically clicking a malicious link. Spain's INCIBE-CERT published the advisory covering this and related issues in the affected password manager.

Critical Impact
Attackers can redirect authenticated users to attacker-controlled domains for credential harvesting and phishing, with limited impact on confidentiality and integrity.

Affected Products

Password manager application referenced in the INCIBE-CERT advisory
Vendor and specific version details were not published in the NVD record at time of writing

Discovery Timeline

2026-06-17 - CVE-2026-10837 published to NVD
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2026-10837

Vulnerability Analysis

The application trusts the X-Forwarded-Host HTTP request header without proper validation. This header is normally set by reverse proxies to indicate the original Host requested by the client. When the application uses this value to construct URLs, such as redirect targets, password reset links, or absolute URLs in server-generated responses, an attacker can override it by sending the header directly.

A victim clicking a link that targets the legitimate application can be redirected to an attacker-controlled domain because the response location is built from attacker-supplied header data. The attacker domain can mimic the legitimate login page, harvest credentials, or deliver malicious payloads. The vulnerability requires user interaction but no authentication or special privileges.

Root Cause

The root cause is missing or inadequate allowlist validation of the X-Forwarded-Host header before using it in URL construction. The application treats client-controllable input as a trusted source for routing or redirect decisions.

Attack Vector

The attack is network-based. An attacker sends a crafted URL pointing to the legitimate application together with a manipulated X-Forwarded-Host header, or convinces the user to follow a link that triggers a response containing the attacker-influenced redirect. The victim's browser then follows the redirect to the attacker domain. See the INCIBE Security Notice for advisory details.

// No verified proof-of-concept code published. The vulnerability
// manifests when the server uses the X-Forwarded-Host value to
// build redirect URLs without validating it against an allowlist.

Detection Methods for CVE-2026-10837

Indicators of Compromise

HTTP requests containing an X-Forwarded-Host header whose value does not match the application's known hostnames
HTTP 3xx responses where the Location header points to an external domain not on the approved list
Web access logs showing redirect chains originating from the application that terminate on suspicious or newly registered domains

Detection Strategies

Inspect reverse proxy and web server logs for inbound X-Forwarded-Host values that differ from the canonical application host
Correlate user-reported phishing attempts against application access logs to identify malicious link patterns
Use web application firewall rules to flag requests where forwarded host headers contain unexpected domains, ports, or encoded characters

Monitoring Recommendations

Alert on outbound redirects to domains outside an explicit allowlist of trusted hosts
Monitor authentication endpoints and password reset flows for anomalous referrer or host header values
Track newly observed external domains appearing in Location headers generated by the application

How to Mitigate CVE-2026-10837

Immediate Actions Required

Apply the vendor patch referenced in the INCIBE-CERT advisory as soon as it is available for your deployment
Audit application code paths that consume X-Forwarded-Host, Forwarded, or X-Forwarded-Proto headers and enforce strict allowlist validation
Notify users of the phishing risk and reinforce that they should inspect URLs before entering credentials

Patch Information

Refer to the INCIBE-CERT advisory on multiple vulnerabilities in the affected password manager for the vendor's remediation guidance. The NVD entry was published on 2026-06-17 and last modified on 2026-06-17. The EPSS score at publication was 0.315%.

Workarounds

Configure the upstream reverse proxy to strip or overwrite client-supplied X-Forwarded-Host headers before forwarding requests to the application
Hardcode the application's canonical hostname when generating absolute URLs instead of deriving them from request headers
Add a web application firewall rule to reject requests where X-Forwarded-Host does not match the expected domain

bash

# Example: strip client-supplied X-Forwarded-Host at an nginx reverse proxy
# so the backend cannot be tricked into building redirects from attacker input
location / {
    proxy_set_header Host              $host;
    proxy_set_header X-Forwarded-Host  $host;
    proxy_set_header X-Forwarded-Proto $scheme;
    proxy_set_header X-Real-IP         $remote_addr;
    proxy_pass http://backend;
}