CVE-2026-10836: HTTP Header Information Disclosure Flaw

CVE-2026-10836 Overview

CVE-2026-10836 is a Host header injection vulnerability caused by improper handling of HTTP headers in a password manager product referenced in an INCIBE security notice. A remote attacker can manipulate the value of the Host header by sending specially crafted HTTP requests to the affected application. Successful exploitation results in the generation of manipulated links or responses. The flaw is classified under [CWE-644: Improper Neutralization of HTTP Headers for Scripting Syntax]. The issue may enable limited information disclosure or compromise the integrity of services that consume the manipulated output, such as password reset workflows or downstream link generation.

Critical Impact
Remote attackers can poison generated URLs and responses, enabling phishing, cache poisoning, or limited information disclosure against dependent services.

Affected Products

Password manager product referenced in the INCIBE advisory (specific vendor and version details not published in NVD)
Web applications that reflect the Host header without validation
Downstream services consuming links generated from the affected component

Discovery Timeline

2026-06-17 - CVE-2026-10836 published to NVD
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2026-10836

Vulnerability Analysis

The vulnerability resides in how the application processes the inbound HTTP Host header. The affected component accepts attacker-controlled header values and reuses them when constructing absolute URLs, redirect targets, or response payloads. Because the header is not validated against an allowlist of expected hostnames, an attacker can substitute an arbitrary domain. Generated links such as password reset URLs or email confirmation links inherit the malicious host. Users who click these links are routed to attacker-controlled infrastructure while retaining valid tokens. The flaw requires user interaction with the crafted output, but no authentication is needed to send the initial request.

Root Cause

The root cause is missing input validation on HTTP headers, specifically the Host header [CWE-644]. The application trusts the header value supplied by the client and propagates it into URL generation routines and response data without sanitization or comparison against a configured canonical hostname.

Attack Vector

The attack vector is network-based. An attacker sends an HTTP request with a forged Host header pointing to an attacker-controlled domain. The server processes the request and emits links, redirects, or response content that embed the malicious value. The attacker then delivers the resulting output, typically via email or web context, to a victim. Refer to the INCIBE Security Notice for vendor-specific details.

Detection Methods for CVE-2026-10836

Indicators of Compromise

HTTP requests where the Host header value does not match the server's canonical domain or configured virtual host
Outbound links in application-generated emails containing unexpected hostnames
Password reset or account confirmation URLs referencing domains outside the organization's allowlist
Web server access logs showing repeated requests from a single source with varying Host header values

Detection Strategies

Inspect web server and application logs for Host header values that deviate from expected hostnames
Compare the Host header against the Server-Name configuration and alert on mismatches
Monitor outbound notification systems for links containing untrusted domains
Deploy WAF rules that reject requests whose Host header is not in an explicit allowlist

Monitoring Recommendations

Aggregate HTTP request metadata in a centralized logging platform and baseline expected Host header values
Alert on anomalies in URL generation patterns within outbound email traffic
Track user-reported phishing attempts that reference legitimate-looking password manager links

How to Mitigate CVE-2026-10836

Immediate Actions Required

Review the INCIBE Security Notice and apply vendor-supplied patches when available
Configure the application or reverse proxy to enforce a fixed canonical hostname
Reject HTTP requests whose Host header does not match the expected production domain
Audit application code paths that consume the Host header for URL or response generation

Patch Information

Vendor patch information is referenced in the INCIBE advisory linked above. NVD does not yet list specific patched versions. Administrators should consult the vendor advisory directly for fixed builds and apply updates as released.

Workarounds

Implement an allowlist of valid Host header values at the web server or reverse proxy layer
Hardcode the canonical hostname used for URL generation rather than deriving it from the request
Disable any debug or default virtual host that accepts arbitrary Host headers
Add WAF signatures that drop requests with malformed or unexpected Host headers

bash

# Example: Nginx configuration to reject unknown Host headers
server {
    listen 443 ssl default_server;
    server_name _;
    return 444;
}

server {
    listen 443 ssl;
    server_name passwords.example.com;
    if ($host != "passwords.example.com") {
        return 444;
    }
    # application proxy configuration follows
}