VulnerabilityPublished 25 Feb 2026

CVE-2026-20091: Cisco Firepower Extensible Operating System (FXOS) · Cross-site Scripting

Affects Cisco Firepower Extensible Operating System (FXOS)Source CVE Database V5

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Not known to be exploited · CVSS 4.8 Medium.

Data as of 29 Oct 2026, 19:04 UTC

CVSS 3.1 base score

4.8Medium

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.2% chance of exploitation in 30 days – higher than 10% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

CVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:C/C:L/I:L/A:N

Attack Vector: Network
Attack Complexity: Low
Privileges Required: High
User Interaction: Required
Scope: Changed
Confidentiality: Low
Integrity: Low
Availability: None

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: High: The attacker is authorized with (i.e., requires) privileges that provide significant (e.g., administrative) control over the vulnerable component that could affect component-wide settings and files.
User Interaction: Required: Successful exploitation of this vulnerability requires a user to take some action before the vulnerability can be exploited.
Scope: Changed: An exploited vulnerability can affect resources beyond the security scope managed by the security authority of the vulnerable component. In this case, the vulnerable component and the impacted component are different and managed by different security authorities.
Confidentiality: Low: There is some loss of confidentiality. Access to some restricted information is obtained, but the attacker does not have control over what information is obtained, or the amount or kind of loss is limited. The information disclosure does not cause a direct, serious loss to the impacted component.
Integrity: Low: Modification of data is possible, but the attacker does not have control over the consequence of a modification, or the amount of modification is limited. The data modification does not have a direct, serious impact on the impacted component.
Availability: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 25 Feb 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 29 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Affected software

Product	Affected	Fixed in
CiscoCisco Firepower Extensible Operating System (FXOS)	Affected 2.14.1.131 – 2.16.0.128 5 affected builds	Fixed in–
CiscoCisco Secure Firewall Adaptive Security Appliance (ASA) Software	Affected 9.12.1 – 9.20.3.20 133 affected builds	Fixed in–
CiscoCisco Unified Computing System (Managed)	Affected 4.0(1a) – 4.3(5e) 85 affected builds	Fixed in–

AI-suggested

Apply official Cisco patches or updates for FXOS versions affected by CVE-2026-20091 as soon as they become available to ensure the vulnerability is remediated.
Restrict administrative access to the FXOS management interface using network segmentation, VPNs, or access control lists to limit exposure to trusted personnel only.
Enforce strong authentication mechanisms, including multi-factor authentication (MFA), for all administrator accounts to reduce the risk of credential compromise.
Regularly audit and monitor administrator account usage and login activity to detect suspicious behavior indicative of compromised credentials.
Educate administrators about the risks of phishing and social engineering that could lead to credential theft and subsequent exploitation of this vulnerability.
Consider implementing Content Security Policy (CSP) headers and other browser security features to mitigate the impact of XSS attacks where possible.
Review and sanitize all user inputs in custom configurations or integrations with the FXOS interface to prevent injection of malicious scripts.
Limit the number of users with administrator or AAA administrator roles to the minimum necessary to reduce the attack surface.

Description

A vulnerability in the web-based management interface of Cisco FXOS Software and Cisco UCS Manager Software could allow an authenticated, remote attacker to conduct a stored cross-site scripting (XSS) attack against a user of the interface. This vulnerability is due to insufficient validation of user-supplied input by the web-based management interface of an affected system. An attacker could exploit this vulnerability by injecting malicious data into specific pages of the interface. A successful exploit could allow the attacker to execute arbitrary script code in the context of the affected interface or access sensitive, browser-based information. To exploit this vulnerability, the attacker must have valid credentials for a user account with the role of Administrator or AAA Administrator. 

Impact

The primary impact of CVE-2026-20091 is the potential compromise of confidentiality and integrity within the Cisco FXOS management interface. An attacker exploiting this vulnerability could execute arbitrary scripts in the context of an administrator's browser session, potentially stealing session cookies, performing unauthorized actions, or manipulating the interface to disrupt management operations. While availability is not directly affected, the breach of administrative control could lead to further attacks or misconfigurations impacting network security. Organizations relying on Cisco FXOS for firewall and security appliance management could face increased risk of insider threats or lateral movement if credentials are compromised. The requirement for valid administrator credentials and user interaction limits the threat to environments where attackers have already gained some level of access, but the consequences remain significant given the privileged nature of the interface. This vulnerability could facilitate persistent access or data exfiltration in targeted attacks against critical network infrastructure.

References

sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-ucsfxosxss-7skVE8Zv (opens in a new tab)

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 27 Feb 2026, 21:25 UTC

Technical details

References

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