Low [CVE-2025-53859] NGINX Open Source and NGINX Plus have a vulnerability in the ngx_mail_smtp_module that might
This low-severity F5 advisory covers CVE-2025-53859; related products: NGINX Plus.
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Summary
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.
Affected versions
No affected-version range was extracted from the source record. The vendor advisory is authoritative — check it before change work.
Official advisory · medium-confidence parse· fetched 3 months ago·verify at source
Fixed versions
No fixed release is recorded yet. That does not prove no patch exists — confirm against the vendor advisory.
Official advisory · medium-confidence parse· fetched 3 months ago·verify at source
Mitigation
The source record does not include mitigation steps. That is not a statement that no fix exists — read the vendor advisory below for the authoritative guidance.
Official advisory · medium-confidence parse· fetched 3 months ago·verify at source
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