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CVE-2026-27651

HIGHCVSS 8.7/10EPSS 0.92%

Last modified

CVE-2026-27651 is a high-severity vulnerability rated 8.7/10 on the CVSS scale. 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. EPSS estimates a 0.92% chance of exploitation in the next 30 days.

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.

Metrics

CVSS 3.1
7.5/10

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

CVSS 4.0
8.7/10

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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

EPSS Probability
0.92%

56.1th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

Affected Software

VendorProductVersions
F5Nginx Open Source>= 0.5.15, <= 0.9.7
F5Nginx Open Source>= 1.0.0, < 1.28.3
F5Nginx Open Source>= 1.29.0, < 1.29.7
F5Nginx Plus>= r33, < r35
F5Nginx Plusr32
F5Nginx Plusr35
F5Nginx Plusr36

References

Timeline

Published
Last Modified
Status
Modified

Frequently Asked Questions

What is CVE-2026-27651?
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.
How severe is CVE-2026-27651?
CVE-2026-27651 has a CVSS score of 8.7/10 (HIGH severity). The EPSS model estimates a 0.92% probability of exploitation in the next 30 days.
How do I fix CVE-2026-27651?
Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

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Source: NVD / NIST