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Vulnerability record · CVE-2026-27651 · published 24 March 2026

CVE-2026-27651: F5 nginx open source null pointer dereference vulnerability

F5 · Nginx Open Source

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.

8.7 CVSS 4.0 High EPSS 1.1% · top 36.9% CWE-476 · NULL pointer dereference
8.7CVSS 4.0 base score
1.1%EPSS exploitation probability, 30 days
NoNot in CISA KEV
2Affected product versions listed by NVD
19References
15 Jul 2026Last modified by NVD

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: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:

Affected products

2 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://my.f5.com/manage/s/article/K000160383 Vendor Advisory
https://access.redhat.com/errata/RHSA-2026:10065
https://access.redhat.com/errata/RHSA-2026:13634
https://access.redhat.com/errata/RHSA-2026:13680
https://access.redhat.com/errata/RHSA-2026:13839
https://access.redhat.com/errata/RHSA-2026:14836
https://access.redhat.com/errata/RHSA-2026:15942
https://access.redhat.com/errata/RHSA-2026:15943
https://access.redhat.com/errata/RHSA-2026:15945
https://access.redhat.com/errata/RHSA-2026:15966
https://access.redhat.com/errata/RHSA-2026:6906
https://access.redhat.com/errata/RHSA-2026:6907
https://access.redhat.com/errata/RHSA-2026:6923
https://access.redhat.com/errata/RHSA-2026:7002
https://access.redhat.com/errata/RHSA-2026:7343
https://access.redhat.com/errata/RHSA-2026:8346
https://access.redhat.com/security/cve/CVE-2026-27651
https://bugzilla.redhat.com/show_bug.cgi?id=2450791
https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-27651.json

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Related vulnerabilities

Same products first, then exploited flaws of the same weakness class.

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Source: NIST National Vulnerability Database (record CVE-2026-27651), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.