CVE-2026-27651 PUBLISHED

NGINX ngx_mail_auth_http_module vulnerability

Assigner: f5
Reserved: 18.03.2026 Published: 24.03.2026 Updated: 24.03.2026

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 Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
CVSS Score: 7.5

Attack Vector	Network	Scope	Unchanged
Attack Complexity	Low	Confidentiality Impact	None
Privileges Required	None	Integrity Impact	None
User Interaction	None	Availability Impact	High

CVSS 3.1

CVSS Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
CVSS Score: 8.7

Exploitability Metrics		Vulnerable System Impact Metrics		Subsequent System Impact Metrics
Attack Vector	Network	Confidentiality	None	Confidentiality	None
Attack Complexity	Low	Integrity	None	Integrity	None
Attack Requirements	None	Availability	High	Availability	None
Privileges Required	None
User Interaction	None

CVSS 4.0

Product Status

Vendor	F5
Product	NGINX Open Source
Versions	Default: unknown affected from 1.29.0 to 1.29.7 (excl.) affected from 0.5.15 to 1.28.3 (excl.)

Vendor	F5
Product	NGINX Plus
Versions	Default: unaffected affected from R36 to R36 P3 (excl.) affected from R35 to R35 P2 (excl.) affected from R34 to * (excl.) affected from R33 to * (excl.) affected from R32 to R32 P5 (excl.)

Credits

F5 acknowledges Arkadi Vainbrand for bringing this issue to our attention and following the highest standards of coordinated disclosure. reporter

References

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

Problem Types

CWE-476 NULL Pointer Dereference CWE