NGINX Plus: Memory Allocation with Excessive Size Value
CVE-2026-42946 is a high-severity memory allocation with excessive size value vulnerability in NGINX Plus from F5, with a CVSS 3.1 base score of 7.4 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 R36 P4, R32 P6 as the first without the flaw, so updating NGINX Plus to one of those releases or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 0.93% chance of exploitation within 30 days, higher than 61% of scored CVEs.
High severity with no evidence of exploitation so far.
What to do
- Update NGINX Plus to R36 P4 or R32 P6, whichever matches your release line, or a later version.
- Update NGINX Open Source to 1.30.1 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 Plus | R36 up to, but not including, R36 P4; R32 up to, but not including, R32 P6 | R36 P4, R32 P6 |
| F5 | NGINX Open Source | 0.8.42 up to, but not including, 1.30.1 | 1.30.1 |
| F5 | Dos | 4.3.0 through 4.7.0; 4.8.0 | Not stated |
| F5 | Nginx Gateway Fabric | 1.3.0 through 1.6.2; 2.0.0 through 2.6.0 | Not stated |
| F5 | Nginx Ingress Controller | 3.5.0 through 3.7.2; 4.0.0 through 4.0.1; 5.0.0 through 5.4.2 | Not stated |
| F5 | Nginx Instance Manager | 2.16.0 through 2.22.0 | Not stated |
| F5 | Waf | 4.9.0 through 4.16.0; 5.1.0 through 5.8.0; 5.9.0 through 5.12.1 | 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
- NoneNothing can be modified.
- 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:N/A:H. Scored by NVD.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 4.0 | 8.3 | High | CNA (f5.com) |
| CVSS 3.1 | 6.5 | Medium | CNA (f5.com) |
| CVSS 3.1 | 7.4 | High | NVD |
Official description
A vulnerability exists in the ngx_http_scgi_module and ngx_http_uwsgi_module modules that may result in excessive memory allocation or an over-read of data. When scgi_pass or uwsgi_pass is configured, an unauthenticated attacker with man-in-the-middle (MITM) ability to control responses from an upstream server may be able to read the memory of the NGINX worker process or restart it. 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: Memory Allocation with Excessive Size Value
The product allocates memory based on an untrusted, large size value, but it does not ensure that the size is within expected limits, allowing arbitrary amounts of memory to be allocated.
How developers prevent this class of flaw
- Perform adequate input validation against any value that influences the amount of memory that is allocated. Define an appropriate strategy for handling requests that exceed the limit, and consider supporting a configuration option so that the administrator can extend the amount of memory to be used if necessary.
- Run your program using system-provided resource limits for memory. This might still cause the program to crash or exit, but the impact to the rest of the system will be minimized.
More Memory Allocation with Excessive Size Value vulnerabilities (CWE-789)
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: partial).
- Record last changed materially (score, affected products, status or references).
References
Advisories
- my.f5.com/manage/s/article/K000161027Mitigation
Other vulnerabilities in NGINX Plus
- 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 Memory Allocation with Excessive Size Value 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
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