NGINX Open Source: NULL Pointer Dereference
CVE-2026-27651 is a high-severity NULL pointer dereference vulnerability in NGINX Open Source from F5, with a CVSS 3.1 base score of 7.5 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. The record lists versions 1.29.7, 1.28.3 as the first without the flaw, so updating NGINX Open Source to one of those releases or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 0.98% chance of exploitation within 30 days, higher than 63% of scored CVEs.
High severity with no evidence of exploitation so far.
What to do
- Update NGINX Open Source to 1.29.7 or 1.28.3, whichever matches your release line, or a later version.
- Update NGINX Plus to R36 P3 or R35 P2 or R32 P5, whichever matches your release line, or a later version.
- Read the advisory on my.f5.com for workarounds and exact fixed builds.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| F5 | NGINX Open Source | 1.29.0 up to, but not including, 1.29.7; 0.5.15 up to, but not including, 1.28.3 | 1.29.7, 1.28.3 |
| F5 | NGINX Plus | R36 up to, but not including, R36 P3; R35 up to, but not including, R35 P2; R34 and later; R33 and later; R32 up to, but not including, R32 P5 | R36 P3, R35 P2, R32 P5 |
| Red Hat | Red Hat Enterprise Linux 10 | Not specified in the record | Not stated |
| Red Hat | Red Hat Enterprise Linux 10.0 Extended Update Support | Not specified in the record | Not stated |
| Red Hat | Red Hat Enterprise Linux 8 | Not specified in the record | Not stated |
| Red Hat | Red Hat Enterprise Linux 9 | Not specified in the record | Not stated |
| Red Hat | Red Hat Enterprise Linux 9.0 Update Services for SAP Solutions | Not specified in the record | Not stated |
| Red Hat | Red Hat Enterprise Linux 9.2 Update Services for SAP Solutions | Not specified in the record | Not stated |
| Red Hat | Red Hat Enterprise Linux 9.4 Extended Update Support | Not specified in the record | Not stated |
| Red Hat | Red Hat Enterprise Linux 9.6 Extended Update Support | Not specified in the record | Not stated |
| Red Hat | Red Hat Hardened Images | Not specified in the record | Not stated |
| Red Hat | Red Hat Update Infrastructure 5 | Not specified in the record | Not stated |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- NoneNo data is disclosed.
- Integrity
- NoneNothing can be modified.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H. Scored by CNA (f5.com).
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 4.0 | 8.7 | High | CNA (f5.com) |
| CVSS 3.1 | 7.5 | High | CNA (f5.com) |
| CVSS 3.1 | 7.5 | High | CNA |
Official 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.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: NULL Pointer Dereference
The product dereferences a pointer that it expects to be valid but is NULL.
How developers prevent this class of flaw
- For any pointers that could have been modified or provided from a function that can return NULL, check the pointer for NULL before use. When working with a multithreaded or otherwise asynchronous environment, ensure that proper locking APIs are used to lock before the check, and unlock when it has finished.
- Select a programming language that is not susceptible to these issues.
- Check the results of all functions that return a value and verify that the value is non-null before acting upon it.
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: yes, technical impact: partial).
- Record last changed materially (score, affected products, status or references).
References
Advisories
Other references
- access.redhat.com/errata/RHSA-2026:10065
- access.redhat.com/errata/RHSA-2026:13634
- access.redhat.com/errata/RHSA-2026:13680
- access.redhat.com/errata/RHSA-2026:13839
- access.redhat.com/errata/RHSA-2026:14836
- access.redhat.com/errata/RHSA-2026:15942
- access.redhat.com/errata/RHSA-2026:15943
- access.redhat.com/errata/RHSA-2026:15945
- access.redhat.com/errata/RHSA-2026:15966
- access.redhat.com/errata/RHSA-2026:6906
- access.redhat.com/errata/RHSA-2026:6907
- access.redhat.com/errata/RHSA-2026:6923
- access.redhat.com/errata/RHSA-2026:7002
- access.redhat.com/errata/RHSA-2026:7343
- access.redhat.com/errata/RHSA-2026:8346
Other vulnerabilities in NGINX Open Source
- 8.1 High severity
- 8.1 High severity
- 8.1 High severity
- 8.2 High severity
- 8.1 High severity
- 8.1 High severity
Recent NULL Pointer Dereference vulnerabilities
- 7.5 High severity
- 7.5 High severity
- 7.5 High severity
- 7.5 High severity
- 7.5 High severity
- 7.5 High severity
Spotted an error? Tell us.