Security readout for executives and security teams
Plain-English summary
This issue affects Cisco Firepower Management Center’s web management interface. An authenticated attacker could cause script code to run in another interface user’s browser if that user interacts with attacker-controlled content. The likely impact is limited theft of browser-accessible information or interface actions, not direct system takeover.
Executive priority
Treat this as a moderate-priority security management-plane issue. It is not described as actively exploited and requires privileges plus user interaction, but FMC access is sensitive. Address during planned maintenance after confirming exposure and vendor-fixed releases.
Technical view
CVE-2021-1239 is multiple stored XSS flaws caused by insufficient validation of user-supplied input in Cisco FMC’s web interface. CVSS is 4.8, with network access, low attack complexity, high privileges required, user interaction required, changed scope, low confidentiality and integrity impact, and no availability impact.
Likely exposure
Exposure is most relevant for organizations running Cisco Firepower Management Center with reachable web administration interfaces and multiple privileged users. The source bundle does not provide affected or fixed version details beyond the product name, so version validation must be done against Cisco’s advisory.
Exploitation context
The source bundle does not show known active exploitation, and the CVE is not marked KEV. Exploitation requires an authenticated remote attacker with high privileges and user interaction, which lowers broad internet risk but matters because FMC is a security management plane.
Researcher notes
The public bundle identifies the product, weakness class, attack conditions, and impact, but not affected or fixed versions. Do not assume exploit availability or broad exposure. Use Cisco’s advisory as the authoritative source for version-specific remediation.
Mitigation direction
- Check Cisco’s advisory for affected and fixed FMC releases.
- Upgrade or patch Cisco FMC according to Cisco guidance.
- Restrict FMC web interface access to trusted management networks.
- Limit FMC accounts to necessary privileged users only.
- Warn administrators against interacting with untrusted FMC interface links.
Validation and detection
- Inventory all Cisco FMC deployments and management URLs.
- Compare deployed FMC versions with Cisco’s advisory.
- Review who can authenticate to FMC with privileged access.
- Confirm administrative access is limited to trusted networks.
- Check monitoring for unusual FMC administrative interface activity.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-79: User-session and phishing behavior lookup
Client-side and session-facing weaknesses should be reviewed alongside initial-access and user-execution behaviors. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupCVE-2021-1239 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- Medium
- CVSS
- 4.8 (3.0)
- Known Exploited
- No
- Published
Vector: CVSS:3.0/AV:N/AC:L/PR:H/UI:R/S:C/C:L/I:L/A:N
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.0/AV:N/AC:L/PR:H/UI:R/S:C/C:L/I:L/A:N1.72.7Primary CVE scoreVulnerability scoring details
Base CVSS 3.0 score
4.8MediumVector: CVSS:3.0/AV:N/AC:L/PR:H/UI:R/S:C/C:L/I:L/A:N
Source materials
- CVE List V5 sourceCVE List V5
- 20210113 Cisco Firepower Management Center Stored Cross-Site Scripting VulnerabilitiesCVE reference · vendor-advisory, x_refsource_CISCO
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.