CVE-2025-53859: nginx: ngx_mail_smtp_module buffer over-read potentially resulting in sensitive information leak

[Solar Designer <solar () openwall com>]

Changes with nginx 1.29.1 include:

    *) Security: processing of a specially crafted login/password when using
       the "none" authentication method in the ngx_mail_smtp_module might
       cause worker process memory disclosure to the authentication server
       (CVE-2025-53859).

----- Forwarded message from Sergey Kandaurov <pluknet () nginx com> -----

From: Sergey Kandaurov <pluknet () nginx com>
Date: Wed, 13 Aug 2025 21:19:56 +0400
To: nginx-announce () nginx org
Subject: [nginx-announce] nginx security advisory (CVE-2025-53859)

A security issue was identified in ngx_mail_smtp_module,
which might allow an attacker to cause buffer over-read,
potentially resulting in sensitive information leak
in a HTTP request to the authentication server (CVE-2025-53859).

The issue happens during the SMTP authentication process and requires
the attacker to make preparations against the target system to extract
the leaked data.

The issue affects nginx 0.7.22-1.29.0.
The issue is fixed in nginx 1.29.1.

For older versions, any of the following measures can be used
as a temporary workaround:

(1) disable the "none" parameter in the "smtp_auth" directive.
(2) remove the "Auth-Wait" header line in the authentication server response.

Patch for the issue can be found here:

https://nginx.org/download/patch.2025.smtp.txt

-- 
Sergey Kandaurov
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----- End forwarded message -----