CVE intelligence and bounded remediation
CVE-2021-23838 — An issue was discovered in flatCore before 2.0.0 build 139
An issue was discovered in flatCore before 2.0.0 build 139. A reflected XSS vulnerability was identified in the media_filter HTTP request body parameter for the acp interface. The affected parameter accepts malicious client-side script without proper input sanitization. For example, a malicious user can leverage this vulnerability to steal cookies from a victim user and perform a session-hijacking attack, which may then lead to unauthorized access to the site.
- Severity
- Medium
- CVSS
- 4.8 (3.1)
- Published
- 2021-01-15
- CISA KEV
- Not currently listed
- Ecosystem
- software/application
- Weaknesses
- CWE-79
Affected products
- flatcore / flatcore
Matched remediation archetype
Cross-site scripting and unsafe browser output
This catalog composition supplies bounded fallback guidance. Explicitly reviewed curated workflows load with the complete record below.
Check exposure
- Trace reflected, stored, and DOM-derived untrusted values into HTML, attributes, URLs, styles, scripts, and client-side template sinks.
- Identify affected origins, authenticated user roles, sensitive browser capabilities, and where content is shared across tenants.
- Review framework escaping, rich-text sanitization, legacy templates, and client-side rendering paths.
Remediate safely
- Use context-aware framework output encoding and safe DOM APIs; keep untrusted data out of executable contexts.
- Sanitize intentionally supported markup with a maintained allowlist policy and validate URLs and attributes separately.
- Update affected rendering components and add tests for every output context using inert sentinel markup.
Authoritative sources
Complete CVE record and remediation plan
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