BIG-IP: Server-Side Request Forgery
CVE-2026-66842 is a high-severity server-side request forgery vulnerability in BIG-IP from F5, with a CVSS 3.1 base score of 8.8 out of 10. It can be exploited remotely over the network by an attacker with a low-privileged account, without any action from a user. The record lists versions 21.1.0.1, 21.0.0.3, 17.5.1.8 as the first without the flaw, so updating BIG-IP to one of those releases or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 0.47% chance of exploitation within 30 days, which is low compared with other CVEs.
High severity with no evidence of exploitation so far.
What to do
- Update BIG-IP to 21.1.0.1 or 21.0.0.3 or 17.5.1.8 or 17.1.3.4, whichever matches your release line, or a later version.
- Update BIG-IQ to 8.4.2.1 or a later version.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| F5 | BIG-IP | 21.1.0 up to, but not including, 21.1.0.1; 21.0.0 up to, but not including, 21.0.0.3; 17.5.0 up to, but not including, 17.5.1.8; 17.1.0 up to, but not including, 17.1.3.4 | 21.1.0.1, 21.0.0.3, 17.5.1.8, 17.1.3.4 |
| F5 | BIG-IQ | 8.4.0 up to, but not including, 8.4.2.1 | 8.4.2.1 |
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
- LowA basic user account is enough.
- 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:L/PR:L/UI:N/S:U/C:H/I:H/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 | 8.8 | High | CNA (f5.com) |
Official description
BIG-IP has a vulnerability where an authenticated user of any role may be able to create administrative user accounts through an undisclosed request to Traffic Management User Interface (TMUI). Impact: This vulnerability may allow an authenticated attacker with network access to the BIG-IP management interface to escalate privileges by creating administrative accounts on the BIG-IP system. There is no data plane exposure; this is a control plane issue only. 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: Server-Side Request Forgery
The web server receives a URL or similar request from an upstream component and retrieves the contents of this URL, but it does not sufficiently ensure that the request is being sent to the expected destination.
How developers prevent this class of flaw
- If there is a known list of applications, IP, hostname, and/or domains to which the product is allowed to communicate, then use allowlists to ensure that outgoing requests are restricted to these known entities. The allowlists could be in the application code or possibly enforced by firewalls or network segmentation.
- If the product is expected to be able to connect to arbitrary IP addresses or domains, consider using a denylist that includes private network addresses, internal domain names, etc. The denylist could be in the application code or possibly enforced by firewalls or network segmentation.
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
Other references
Other vulnerabilities in BIG-IP
- 9.8 Critical severity
F5 BIG-IP APM Heap-based Buffer Overflow Exploited
- 7.5 High severity
- 8.7 High severity
- 8.7 High severity
- 7.5 High severity
- 7.5 High severity
Recent Server-Side Request Forgery vulnerabilities
- 8.8 High severity
- 7.4 High severity
- 8.3 High severity
- 7.7 High severity
- 7.7 High severity
- 7.3 High severity
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