CVE-2026-63020 in BIG-IP
Summary
by MITRE • 09/02/2026
A vulnerability exists in an undisclosed BIG-IP Configuration utility page that may allow an attacker to spoof error messages
Impact:
An attacker may trick authenticated BIG-IP users into accessing malicious links and reflect a spoofed error message in the victim's BIG-IP Configuration utility web browser session. This is a control plane issue; there is no data plane exposure.
Note: Software versions which have reached End of Technical Support (EoTS) are not evaluated.
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Analysis
by VulDB Data Team • 09/02/2026
The disclosed vulnerability resides within an undisclosed configuration utility page of the F5 BIG-IP platform, presenting a significant risk to authenticated users through social engineering and session manipulation techniques. This flaw is classified as a control plane issue, meaning it affects the management interface used by administrators for system configuration rather than the data plane responsible for forwarding network traffic. Consequently, while the vulnerability does not provide direct access to sensitive user data or allow for lateral movement within the internal network infrastructure via packet injection, it poses a severe threat to the integrity of administrative operations and trust in the management console itself. The core technical flaw involves the application's handling of error states during specific configuration tasks, where an attacker can manipulate parameters to force the system to reflect maliciously crafted content as part of standard error messages displayed within the web browser session.
From a technical perspective, this vulnerability aligns with CWE-79, which covers Cross-Site Scripting (XSS), specifically in its reflected variant. The mechanism allows an adversary to craft a URL containing specific arguments or parameters that trigger a system-level error condition. When an authenticated administrator clicks on such a link, the BIG-IP Configuration utility processes the request and generates an error response. Due to insufficient sanitization of these input parameters within the context of the error message display logic, the malicious content is injected directly into the HTML output rendered by the browser. This enables the attacker to spoof legitimate system warnings or errors, potentially displaying fake prompts that mimic official F5 security alerts, license expiration notices, or configuration failure messages designed to deceive the user into taking unintended actions such as downloading malware, entering credentials on a phishing site, or disabling critical security features based on false premises.
The operational impact of this vulnerability is primarily centered around trust erosion and potential credential theft via sophisticated social engineering attacks. Since the attack requires an authenticated session, it targets privileged users who have already bypassed initial authentication barriers. An attacker could distribute these malicious links through phishing emails, compromised internal communication channels, or other vectors that trick administrators into clicking them while logged into their BIG-IP management interface. Once clicked, the spoofed error message appears within the trusted context of the application's domain and user session. This increases the likelihood of success because users are more likely to trust messages appearing in a familiar environment they have already authenticated against. The attacker could use this deception to harvest sensitive information, such as two-factor authentication codes or secondary passwords, by directing the victim to a counterfeit login page that mimics the BIG-IP interface but captures credentials for subsequent unauthorized access.
In terms of industry standard mapping, this vulnerability is closely associated with MITRE ATT&CK technique T1078, which involves Valid Accounts and specifically the misuse of legitimate administrative privileges through social engineering. It also relates to T1566, Phishing, where the initial vector relies on deceiving users into interacting with malicious content. The lack of input validation in error handling routines represents a common pattern in web application security flaws, often categorized under CWE-20 Improper Input Validation when combined with CWE-79 Cross-site Scripting. These classifications highlight that while the immediate exploitation does not compromise network data integrity, it undermines the administrative control layer which is critical for maintaining overall system security posture.
Mitigation strategies must focus on both technical remediation and user awareness training. F5 Networks has released patches to address this specific flaw in supported software versions; therefore, the primary defensive measure is to apply the latest available updates immediately. Organizations should verify their current BIG-IP version against the list of End of Technical Support (EoTS) releases, as older unsupported versions are not evaluated for such vulnerabilities and may remain exposed indefinitely. Additionally, implementing strict Content Security Policy headers can help mitigate the impact by restricting how scripts execute within the browser context, although this is a secondary defense since the root cause lies in server-side input handling. User education remains critical; administrators should be trained to scrutinize unexpected error messages, verify URLs before clicking links received via email or chat, and report any anomalous behavior in the management interface to security teams immediately. Regular audits of administrative access logs can also help detect unusual patterns that might indicate attempted exploitation through social engineering tactics targeting this specific control plane weakness.