CVE-2026-39455: File Descriptor Exhaustion in F5 BIG-IP
Platform
linux
Component
bigip
Fixed in
21.0.0.2
CVE-2026-39455 affects F5 BIG-IP systems utilizing Lightweight Directory Access Protocol (LDAP) authentication. A misconfiguration can trigger an undisclosed traffic pattern, causing the httpd process to exhaust available file descriptors, resulting in a denial-of-service condition. This vulnerability impacts versions 16.1.0 through 21.0.0.2, and a fix is available in version 21.0.0.2.
Impact and Attack Scenarios
Successful exploitation of CVE-2026-39455 can lead to a denial-of-service (DoS) attack, rendering the affected BIG-IP system unavailable. This disruption can impact critical services relying on the BIG-IP infrastructure, such as load balancing, web application delivery, and security features. The impact extends beyond the immediate system, potentially affecting applications and users dependent on the BIG-IP's functionality. While the vulnerability doesn't directly expose sensitive data, the DoS can disrupt operations and potentially mask other malicious activity. The blast radius is limited to the services managed by the affected BIG-IP instance.
Exploitation Context
CVE-2026-39455 has been published on 2026-05-13. Its severity is rated HIGH (CVSS 7.5). Public proof-of-concept (POC) code is currently unavailable. The vulnerability is not listed on KEV or EPSS, suggesting a low to medium probability of exploitation in the short term. Monitor F5 security advisories and threat intelligence feeds for updates.
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
- None — unauthenticated. No login or credentials needed to exploit.
- User Interaction
- None — attack is automatic and silent. Victim does nothing: no click, no file open.
- Scope
- Unchanged — impact is limited to the vulnerable component itself.
- Confidentiality
- None — no confidentiality impact. Attacker cannot read protected data.
- Integrity
- None — no integrity impact. Attacker cannot modify data.
- Availability
- High — complete crash or resource exhaustion. Full denial of service.
Affected Software
Weakness Classification (CWE)
Timeline
- Reserved
- Published
Mitigation and Workarounds
The primary mitigation for CVE-2026-39455 is upgrading to F5 BIG-IP version 21.0.0.2 or later, which includes the fix. If immediate upgrade is not feasible, implement temporary workarounds. Configure a Web Application Firewall (WAF) or proxy to limit or filter LDAP traffic to the BIG-IP system, specifically targeting the traffic pattern that triggers the file descriptor exhaustion. Review LDAP authentication configurations to ensure they adhere to security best practices and minimize unnecessary LDAP traffic. After upgrading, verify the fix by attempting to reproduce the vulnerability with the traffic pattern described in the advisory; the httpd process should not exhaust file descriptors.
How to fix
Actualice a una versión corregida de BIG-IP. Las versiones afectadas incluyen 17.5.1.6, 17.1.3.2, 21.0.0.2 y versiones posteriores de 21.1.0. Consulte la documentación de F5 para obtener instrucciones detalladas de actualización y mitigación.
Frequently asked questions
What is CVE-2026-39455 — File Descriptor Exhaustion in F5 BIG-IP?
CVE-2026-39455 is a HIGH severity vulnerability in F5 BIG-IP allowing LDAP authentication misconfigurations to exhaust file descriptors, causing a denial-of-service. It affects versions 16.1.0–21.0.0.2.
Am I affected by CVE-2026-39455 in F5 BIG-IP?
You are affected if you are running F5 BIG-IP versions 16.1.0 through 21.0.0.2 and have LDAP authentication enabled. Carefully review your LDAP configuration.
How do I fix CVE-2026-39455 in F5 BIG-IP?
Upgrade to F5 BIG-IP version 21.0.0.2 or later. As a temporary workaround, implement WAF rules to limit LDAP traffic.
Is CVE-2026-39455 being actively exploited?
Currently, there are no public reports of CVE-2026-39455 being actively exploited, but monitoring is crucial.
Where can I find the official F5 advisory for CVE-2026-39455?
Refer to the official F5 security advisory for CVE-2026-39455 on the F5 website: [https://www.f5.com/security/center/advisory/f5-security-advisory-26-07.html](https://www.f5.com/security/center/advisory/f5-security-advisory-26-07.html)
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