Information Disclosure via X-OWA-Version Header

Description

The 'X-OWA-Version' header indicates which version of Outlook Web App (OWA) is being used by the application, potentially revealing exact build or release details. Attackers can leverage this information to target known vulnerabilities, unpatched issues, or default configurations tied to that specific OWA release. Moreover, discovering the OWA version can enable malicious actors to craft phishing campaigns or social engineering techniques that exploit OWA-specific features. Ultimately, leaking version data increases the risk of a successful attack by guiding adversaries to well-documented weaknesses or version-specific exploits within Outlook Web App components.

Remediation

Remove or mask the 'X-OWA-Version' header to prevent external parties from identifying the exact OWA release. Configure the mail server or application layer settings to strip or rewrite this header before sending responses to untrusted clients. Keep your Outlook Web App instance updated with the latest patches and security advisories from Microsoft to minimize exploitable vulnerabilities. If reverse proxies, load balancers, or CDNs are in use, ensure they do not preserve or re-inject version-related headers. Additionally, employ a Web Application Firewall (WAF) or intrusion detection system to detect and block suspicious requests attempting to exploit known OWA weaknesses. Regularly review your header configurations and logs to confirm that no sensitive version data is inadvertently leaked.

References

Severity

Owasp

Code: A05:2021

Category: Security Misconfiguration

Classification