Attack Chain

1. An unauthenticated attacker identifies a MailGates/MailAudit instance exposed to the internet.
2. The attacker crafts a malicious HTTP request containing CRLF sequences within a vulnerable parameter (e.g., URL or header value).
3. The CRLF sequences are injected into an HTTP header, allowing the attacker to insert additional headers or manipulate existing ones.
4. By injecting a Content-Type header followed by a blank line and arbitrary content, the attacker attempts to inject data into the HTTP response body.
5. The server processes the crafted request without properly sanitizing the CRLF sequences.
6. The injected content, which could include commands to read system files, is interpreted by the server.
7. The server responds with the content of the requested system file within the HTTP response.
8. The attacker retrieves the sensitive information from the server’s response, achieving unauthorized access to system files.

Impact

Successful exploitation of this CRLF injection vulnerability (CVE-2026-6351) can lead to unauthorized access to sensitive system files on the affected MailGates/MailAudit server. This can result in the disclosure of confidential information, such as usernames, passwords, configuration details, and other sensitive data. The number of potential victims is dependent on the number of organizations using vulnerable versions of Openfind MailGates/MailAudit. The affected sectors are likely those that rely on these applications for email security and auditing. The consequences of a successful attack include data breaches, potential regulatory fines, and reputational damage.

Recommendation

• Apply the patches or updates provided by Openfind to address CVE-2026-6351 as soon as they become available.
• Implement input validation and sanitization on all user-supplied data to prevent CRLF injection attacks (reference CWE-93).
• Deploy the Sigma rule Detect Suspicious CRLF Injection Attempts to identify potential exploitation attempts targeting this vulnerability.
• Monitor web server logs for unusual patterns or unexpected characters in HTTP headers, specifically looking for CRLF sequences (\r\n) to detect potential exploitation attempts. Enable webserver logging to activate the rule above.