Denial of Service in NGINX ngx_mail_auth_http_module via Auth-Wait

Publication date: 2026-03-24

Last updated on: 2026-06-30

Assigner: F5 Networks

Description

When the ngx_mail_auth_http_module module is enabled on NGINX Plus or NGINX Open Source, undisclosed requests can cause worker processes to terminate. This issue may occur when (1) CRAM-MD5 or APOP authentication is enabled, and (2) the authentication server permits retry by returning the Auth-Wait response header. Note: Software versions which have reached End of Technical Support (EoTS) are not evaluated.

CVSS Scores

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Meta Information

Published

2026-03-24

Last Modified

2026-06-30

Generated

2026-07-06

AI Q&A

2026-03-24

EPSS Evaluated

2026-07-05

NVD

CVE-2026-27651

EUVD

EUVD-2026-14880

Affected Vendors & Products

Vendor	Product	Version / Range
f5	nginx_plus	r32
f5	nginx_plus	r32
f5	nginx_plus	r32
f5	nginx_plus	r32
f5	nginx_plus	r35
f5	nginx_plus	r36
f5	nginx_plus	r36
f5	nginx_plus	From r33 (inc) to r35 (exc)
f5	nginx_plus	r35
f5	nginx_plus	r36
f5	nginx_open_source	From 1.29.0 (inc) to 1.29.7 (exc)
f5	nginx_plus	r32
f5	nginx_open_source	From 1.0.0 (inc) to 1.28.3 (exc)
f5	nginx_open_source	From 0.5.15 (inc) to 0.9.7 (inc)

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-476	The product dereferences a pointer that it expects to be valid but is NULL.

Attack-Flow Graph

Executive Summary

This vulnerability occurs in the ngx_mail_auth_http_module module when it is enabled on NGINX Plus or NGINX Open Source. Specifically, if CRAM-MD5 or APOP authentication is enabled and the authentication server allows retries by returning the Auth-Wait response header, certain undisclosed requests can cause the worker processes to terminate unexpectedly.

Impact Analysis

The impact of this vulnerability is that it can cause worker processes in NGINX to terminate, leading to potential denial of service. This means that the affected server could become unavailable or unstable, disrupting services that rely on NGINX for mail authentication.

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