CVE-2025-53859 NGINX ngx_mail_smtp_module vulnerability
Unauthenticated attackers can leak arbitrary memory bytes from the SMTP authentication process if specific non-default configurations are enabled.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2025-53859?
CVE-2025-53859 is a medium-severity vulnerability in F5 NGINX Open Source, published on 13 Aug 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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.
Weakness: CWE-125
Which versions are affected by CVE-2025-53859?
2 open source packages ship an affected version, including nginx and nginx-gateway. It affects 2 products.
| Package | Affected | Fixed in |
|---|---|---|
nginx Bitnami | From 0.7.0 | 1.29.1 |
nginx-gateway Bitnami | From 0.7.0 | 1.29.1 |
Linux distribution packages (1)
nginx openSUSE:Tumbleweed | All versions | 1.29.1-1.1 |
Products include F5 Nginx Open Source, F5 Nginx Plus.
How do I fix CVE-2025-53859?
Upgrade nginx to 1.29.1 or later.
Is CVE-2025-53859 being exploited?
There is no known exploitation of CVE-2025-53859 in the wild and no public exploit code.
Other vulnerabilities in F5 NGINX Open Source
Sources
Also known as ALPINE-CVE-2025-53859, AZL-66308, AZL-66311, BELL-CVE-2025-53859, BIT-nginx-2025-53859, BIT-nginx-gateway-2025-53859 and 17 more.