CVE-2026-27651

NGINX ngx_mail_auth_http_module vulnerability

HIGH

7.5

CVSS Score

Published: March 24, 2026 at 02:13 PM UTC

Updated: July 15, 2026 at 02:19 AM UTC

2 products affected across 1 vendorNGINX PlusNGINX Open Source

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Severity

HIGH7.5

Exploit prediction

EPSS 1.0%

SSVC

No known exploit

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.

Affected

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

NGINX Open Source · F5

95%

0.5.15 ≤ v ≤ 0.9.70.5.15 ≤ v < 1.28.31.0.0 ≤ v < 1.28.31.29.0 ≤ v < 1.29.70.5.15 1.29.0

Affected range stops below 1.28.3, so it looks safe — our inference, not a vendor statement

Affected range stops below 1.29.7, so it looks safe — our inference, not a vendor statement

NGINX Plus · F5

95%

v ≥ R33v ≥ R34R32 ≤ v < R32 P5R35 ≤ v < R35 P2R36 ≤ v < R36 P3r33 ≤ v < r35R32 R33 R34 R35 R36 r32 r32 p1 r32 p2 r32 p3 r32 p4r35r35 p1 r36 r36 p1 r36 p2

Affected range stops below R32 P5, so it looks safe — our inference, not a vendor statement

Affected range stops below R35 P2, so it looks safe — our inference, not a vendor statement

Affected range stops below R36 P3, so it looks safe — our inference, not a vendor statement

Affected range stops below r35, so it looks safe — our inference, not a vendor statement

Remediation

No guide yet

No remediation guidance has been written for this CVE yet. What the record does show:

Patch and advisory references

https://my.f5.com/manage/s/article/K000160383