NGINX Open Source: Use After Free
CVE-2026-42530 is a high-severity use after free vulnerability in NGINX Open Source from F5, with a CVSS 3.1 base score of 8.1 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. The record lists version 1.31.2 as the first without the flaw, so updating NGINX Open Source to that release or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 6.22% chance of exploitation within 30 days, which is in the top 6.36% of all scored CVEs.
High severity with no evidence of exploitation so far.
What to do
- Update NGINX Open Source to 1.31.2 or a later version.
- Update Nginx Gateway Fabric to 2.6.4 or a later version.
- Update Nginx Ingress Controller to 5.5.1 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 | 1.31.0 up to, but not including, 1.31.2 | 1.31.2 |
| Red Hat | Red Hat Hardened Images | Not specified in the record | Not stated |
| Red Hat | Red Hat Enterprise Linux 10 | 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 Lightspeed proxy 1 | Not specified in the record | Not stated |
| F5 | Nginx Gateway Fabric | 1.3.0 through 1.6.2; 2.0.0 up to, but not including, 2.6.4 | 2.6.4 |
| F5 | Nginx Ingress Controller | 3.5.0 through 3.7.2; 5.0.0 up to, but not including, 5.5.1; 4.0.0; 4.0.1 | 5.5.1 |
| F5 | Nginx Instance Manager | 2.17.0 through 2.22.0 | 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
- HighSuccess depends on conditions outside the attacker's control.
- 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
- HighAll data handled by the component can be read.
- Integrity
- HighData or code can be modified at will.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H. Scored by CNA (f5.com).
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 4.0 | 9.2 | Critical | CNA (f5.com) |
| CVSS 3.1 | 8.1 | High | CNA (f5.com) |
| CVSS 3.1 | 8.1 | High | CNA |
Official description
NGINX Open Source has a vulnerability in the ngx_http_v3_module module. When NGINX Open Source is configured to use the HTTP/3 QUIC module, a remote unauthenticated attacker along with conditions beyond their control can use a specially crafted HTTP/3 session to reopen a QPACK encoder stream. This may cause a Use-after-Free in the NGINX worker process leading to a restart. Additionally, attackers can execute code on systems with Address Space Layout Randomization (ASLR) disabled or when the attacker can bypass ASLR. 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: Use After Free
The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory belongs to the code that operates on the new pointer.
How developers prevent this class of flaw
- Choose a language that provides automatic memory management.
- When freeing pointers, be sure to set them to NULL once they are freed. However, the utilization of multiple or complex data structures may lower the usefulness of this strategy.
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: total).
- Record last changed materially (score, affected products, status or references).
References
Advisories
Third-party and government advisories
- access.redhat.com/security/cve/CVE-2026-42530Third Party Advisory
- bugzilla.redhat.com/show_bug.cgi?id=2489872Third Party Advisory
- security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-42530.jsonThird Party Advisory
Other references
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 Use After Free vulnerabilities
- 8.3 High severity
- 8.3 High severity
- 7.5 High severity
- 7.5 High severity
- 8.8 High severity
- 8.3 High severity
Spotted an error? Tell us.