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.

Metrics

Attack Vector Network

Attack Complexity Low

Privileges Required None

Attack Requirements Present

User Interaction None

Vulnerable System Confidentiality Impact Low

Vulnerable System Integrity Impact None

Vulnerable System Availability Impact None

Subsequent System Confidentiality Impact None

Subsequent System Integrity Impact None

Subsequent System Availability Impact None

Attack Vector Network

Attack Complexity High

Privileges Required None

Scope Unchanged

Confidentiality Impact Low

Integrity Impact None

Availability Impact None

User Interaction None

No CVSS v3.0

No CVSS v2

This CVE is not in the KEV list.

Exploitation none

Automatable no

Technical Impact partial

Affected Vendors & Products

Vendors Products
F5
  • Nginx Open Source
  • Nginx Plus
Nginx
  • Nginx

No data.

No data.

References
Link Providers
https://my.f5.com/manage/s/article/K000152786 cve-icon cve-icon cve-icon
https://nvd.nist.gov/vuln/detail/CVE-2025-53859 cve-icon
https://www.cve.org/CVERecord?id=CVE-2025-53859 cve-icon
History

Sat, 16 Aug 2025 21:45:00 +0000

Type Values Removed Values Added
First Time appeared F5
F5 nginx Open Source
F5 nginx Plus
Nginx
Nginx nginx
Vendors & Products F5
F5 nginx Open Source
F5 nginx Plus
Nginx
Nginx nginx

Thu, 14 Aug 2025 06:30:00 +0000

Type Values Removed Values Added
References
Metrics threat_severity

None

 threat_severity

Low

Wed, 13 Aug 2025 16:15:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Wed, 13 Aug 2025 15:00:00 +0000

Type Values Removed Values Added
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.
Title NGINX ngx_mail_smtp_module vulnerability
Weaknesses CWE-125
References
Metrics cvssV3_1

{'score': 3.7, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N'}

cvssV4_0

{'score': 6.3, 'vector': 'CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N'}
cve-icon MITRE

Status: PUBLISHED

Assigner: f5

Published:

Updated: 2025-08-13T15:14:55.021Z

Reserved: 2025-07-29T17:12:25.039Z

Link: CVE-2025-53859

cve-icon Vulnrichment

Updated: 2025-08-13T15:14:51.817Z

cve-icon NVD

Status : Awaiting Analysis

Published: 2025-08-13T15:15:37.657

Modified: 2025-08-13T17:33:46.673

Link: CVE-2025-53859

cve-icon Redhat

Severity : Low

Publid Date: 2025-08-13T14:46:55Z

Links: CVE-2025-53859 - Bugzilla