CVE-2025-53859

Description

NGINX Open Source and NGINX Plus have a vulnerability in the ngx_mail_smtp_module that might allow an unauthenticated attacker to over-read NGINX SMTP authentication process memory; as a result, the server side may leak arbitrary bytes sent in a request to the authentication server. This issue happens during the NGINX SMTP authentication process and requires the attacker to make preparations against the target system to extract the leaked data. The issue affects NGINX only if (1) it is built with the ngx_mail_smtp_module, (2) the smtp_auth directive is configured with method "none," and (3) the authentication server returns the "Auth-Wait" response header. Note: Software versions which have reached End of Technical Support (EoTS) are not evaluated.

How to fix CVE-2025-53859

To remediate CVE-2025-53859, upgrade the affected package to a fixed version below.

• —upgrade to 1.28.2-r0 or later
• —upgrade to 1.29.1 or later
• —upgrade to 1.29.1 or later
• —upgrade to 1.18.0-6.1+deb11u6 or later

Is CVE-2025-53859 being exploited?

Low — EPSS is 0.0%, meaning exploitation activity has not been observed at scale.

Affected packages (4)

• from 0, < 1.28.2-r0
• >= 0.7.0, < 1.29.1
• >= 0.7.0, < 1.29.1
• from 0, < 1.18.0-6.1+deb11u6

CVSS scores

References (5)

• ADVISORYsecurity.alpinelinux.org/vuln/CVE-2025-53859
• ADVISORYsecurity-tracker.debian.org/tracker/CVE-2025-53859
• WEBmy.f5.com/manage/s/article/K000152786
• WEBnvd.nist.gov/vuln/detail/CVE-2025-53859
• WEB