# CVE-2026-27651: NGINX NULL pointer dereference in ngx_mail_auth_http_module

Source: https://junglewise.ai/threats/cve-2026-27651-nginx-null-pointer-dereference-in-ngx-mail-auth-http-module  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-03-24. Updated: 2026-06-30  
License: CC BY 4.0 with a link back

CVE-2026-27651 · Severity: high · CVSS 7.5 · Published 2026-03-24

NGINX is a widely used web and proxy server that also handles email traffic. A vulnerability in its mail authentication module allows a remote attacker to crash the server's worker processes by sending specific requests. This results in a denial of service, preventing the server from processing legitimate traffic and potentially disrupting email services.

Technologies: [F5 Nginx Plus](https://junglewise.ai/threats/technologies/nginx-plus), [NGINX Open Source](https://junglewise.ai/threats/technologies/open-source). Vendors: [F5](https://junglewise.ai/threats/vendors/f5), [NGINX](https://junglewise.ai/threats/vendors/nginx).

## Quick answers

**Is CVE-2026-27651 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-27651 being exploited in the wild.

**How severe is CVE-2026-27651?** High severity, with a CVSS score of 7.5, published 24 March 2026.

**Which products and versions are affected?** NGINX NGINX Open Source; F5 NGINX Plus; Red Hat Enterprise Linux 8, 9, 10.0, 10.1.

**Is there a fix for CVE-2026-27651?** A patch was published on 2026-04-23: Red Hat released security updates (RHSA-2026:10065) Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-27651 attacked?** It is attacked over the network, in a web application.

**Am I affected by CVE-2026-27651?** Check whether you run F5 Nginx Plus or NGINX Open Source. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

A NULL pointer dereference vulnerability (CWE-476) exists in the ngx_mail_auth_http_module of NGINX. The issue is triggered when CRAM-MD5 or APOP authentication is enabled and the upstream authentication server returns an 'Auth-Wait' response header to permit a retry. An attacker can send undisclosed requests that cause NGINX worker processes to terminate, leading to a denial of service. The vulnerability is reachable over the network without authentication. Patches have been released by NGINX and various Linux distributions including Red Hat.

## Affected products

- NGINX NGINX Open Source
- F5 NGINX Plus
- Red Hat Enterprise Linux 8, 9, 10.0, 10.1

## Timeline

- 2026-03-24: disclosed
- 2026-03-24: advisory: Initial NVD publication
- 2026-04-23: patched: Red Hat released security updates (RHSA-2026:10065)

## References

- [https://my.f5.com/manage/s/article/K000160383](https://my.f5.com/manage/s/article/K000160383)
- [https://access.redhat.com/errata/RHSA-2026:10065](https://access.redhat.com/errata/RHSA-2026:10065)
- [https://access.redhat.com/errata/RHSA-2026:13634](https://access.redhat.com/errata/RHSA-2026:13634)
- [https://access.redhat.com/errata/RHSA-2026:13680](https://access.redhat.com/errata/RHSA-2026:13680)
- [https://access.redhat.com/errata/RHSA-2026:13839](https://access.redhat.com/errata/RHSA-2026:13839)
- [https://access.redhat.com/errata/RHSA-2026:14836](https://access.redhat.com/errata/RHSA-2026:14836)
- [https://access.redhat.com/errata/RHSA-2026:15942](https://access.redhat.com/errata/RHSA-2026:15942)

## Related threats

- [NGINX Plus and Open Source heap buffer overflow in alias directive with rewrite](https://junglewise.ai/threats/cve-2026-15176-a-vulnerability-exists-in-nginx-plus-and-nginx-open-source-when-a)
- [NGINX Plus and Open Source HTTP/3 heap buffer overflow in TLS handshake](https://junglewise.ai/threats/cve-2026-90439-nginx-plus-and-open-source-http-3-heap-buffer-overflow-in-tls)
- [NGINX uninitialized memory access in ngx_http_slice_module](https://junglewise.ai/threats/cve-2026-60005-nginx-uninitialized-memory-access-in-ngx-http-slice-module)
- [F5 NGINX Plus heap buffer over-read in MQTT filter module](https://junglewise.ai/threats/cve-2026-60065-f5-nginx-plus-heap-buffer-over-read-in-mqtt-filter-module)
- [F5 NGINX heap buffer over-read in ngx_http_ssi_module](https://junglewise.ai/threats/cve-2026-56434-f5-nginx-heap-buffer-over-read-in-ngx-http-ssi-module)