CVE-2026-42406: Privilege Escalation in F5 BIG-IP
Platform
linux
Component
bigip
Fixed in
21.0.0.2
CVE-2026-42406 describes a privilege escalation vulnerability within F5 BIG-IP and BIG-IQ systems. A highly privileged, authenticated attacker possessing the Certificate Manager role can exploit this flaw to modify configuration objects, ultimately enabling the execution of arbitrary commands. This vulnerability impacts versions 16.1.0 through 21.0.0.2; a fix is available in version 21.0.0.2.
Impact and Attack Scenarios
The impact of CVE-2026-42406 is significant due to the potential for complete system compromise. An attacker who can successfully exploit this vulnerability gains the ability to run arbitrary commands with elevated privileges. This could lead to data exfiltration, system modification, denial of service, or even complete control of the BIG-IP appliance. The Certificate Manager role, while privileged, is often granted to multiple users, expanding the attack surface. Successful exploitation could allow an attacker to bypass existing security controls and gain persistent access to the network behind the BIG-IP device, facilitating lateral movement and impacting other systems. This vulnerability shares similarities with other configuration manipulation vulnerabilities where attackers leverage existing privileges to escalate their access.
Exploitation Context
CVE-2026-42406 was published on May 13, 2026. Its severity is currently assessed as HIGH (CVSS: 8.7). Public proof-of-concept (POC) code is not currently available, but the vulnerability's nature suggests a high likelihood of exploitation once a POC is released. The vulnerability is not currently listed on KEV or EPSS, indicating a low to medium probability of active exploitation at this time. Refer to the official F5 advisory for further details.
Threat Intelligence
Exploit Status
CISA SSVC
CVSS Vector
What do these metrics mean?
- Attack Vector
- Network — remotely exploitable over the internet. No physical or local access required. Widest attack surface.
- Attack Complexity
- Low — no special conditions required. Attacker can exploit reliably without depending on rare configurations or timing.
- Privileges Required
- High — admin or privileged account required to exploit.
- User Interaction
- None — attack is automatic and silent. Victim does nothing: no click, no file open.
- Scope
- Changed — successful attack can pivot beyond the vulnerable component to other systems or the host OS.
- Confidentiality
- High — complete confidentiality loss. Attacker can read all data: credentials, keys, personal data.
- Integrity
- High — attacker can write, modify, or delete any data: databases, config files, or code.
- Availability
- None — no availability impact. Service remains fully operational.
Affected Software
Weakness Classification (CWE)
Timeline
- Reserved
- Published
Mitigation and Workarounds
The primary mitigation for CVE-2026-42406 is to upgrade to F5 BIG-IP version 21.0.0.2 or later. If immediate upgrade is not feasible, consider implementing stricter access controls for the Certificate Manager role, limiting its scope and privileges. Review existing configuration objects for any unauthorized modifications. Implement Web Application Firewall (WAF) rules to detect and block suspicious command execution attempts. Monitor BIG-IP logs for unusual activity, particularly related to configuration changes and command execution. After upgrading, verify the fix by attempting to modify a configuration object with the Certificate Manager role and confirming that the action is denied.
How to fix
Actualice a una versión corregida de BIG-IP o BIG-IQ. F5 ha publicado parches para solucionar esta vulnerabilidad. Consulte la nota de seguridad K000160971 en el sitio web de F5 para obtener más detalles sobre las versiones afectadas y las versiones corregidas.
Frequently asked questions
What is CVE-2026-42406 — Privilege Escalation in F5 BIG-IP?
CVE-2026-42406 is a HIGH severity vulnerability affecting F5 BIG-IP and BIG-IQ systems. It allows an authenticated attacker with the Certificate Manager role to execute arbitrary commands, potentially leading to system compromise.
Am I affected by CVE-2026-42406 in F5 BIG-IP?
You are potentially affected if you are running F5 BIG-IP or BIG-IQ versions between 16.1.0 and 21.0.0.2. Check your version and upgrade if necessary.
How do I fix CVE-2026-42406 in F5 BIG-IP?
Upgrade to F5 BIG-IP version 21.0.0.2 or later. As an interim measure, restrict access to the Certificate Manager role and monitor logs for suspicious activity.
Is CVE-2026-42406 being actively exploited?
While no active exploitation is currently confirmed, the vulnerability's nature suggests a high likelihood of exploitation once a proof-of-concept is released. Monitor security advisories and threat intelligence feeds.
Where can I find the official F5 advisory for CVE-2026-42406?
Refer to the official F5 Security Advisory for CVE-2026-42406 on the F5 website. Search for 'F5 Security Advisory CVE-2026-42406' to locate the advisory.
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