Bulwark Webmail, a self-hosted webmail client for Stalwart Mail Server, has a vulnerability (CVE-2026-35391) in versions before 1.4.11 where the getClientIP() function in lib/admin/session.ts incorrectly trusts the first (leftmost) IP address in the X-Forwarded-For HTTP header. Since this header is fully client-controlled, an attacker can supply a forged IP address. This can be exploited to bypass IP-based rate limiting mechanisms, facilitating brute-force attacks on the admin login, and to forge audit logs, making malicious actions appear to originate from arbitrary IPs. The vulnerability is classified under CWE-348 (Use of Less Trusted Source) and has a CVSS 4.0 score of 8.7 (high severity). The vulnerability is fixed in Bulwark Webmail version 1.4.11.

An attacker can bypass IP-based rate limiting protections by forging the X-Forwarded-For header, enabling brute-force attacks against the admin login. Additionally, audit logs can be manipulated to hide the true source of malicious activity by forging IP addresses. This undermines both access control and forensic capabilities of the affected system.

Upgrade Bulwark Webmail to version 1.4.11 or later, where this vulnerability is fixed. Since the vendor advisory confirms the issue is resolved in 1.4.11, applying this official fix is the recommended remediation. No other mitigation steps are indicated.