Inspect HTTP Set-Cookie response headers to verify session protection flags. Detect missing HttpOnly (XSS leakage), unencrypted transmission (Secure flag missing), and CSRF vulnerabilities in SameSite policies.
The Cookie Security Checker inspects HTTP Set-Cookie headers on any public web application to audit critical defensive attributes: the Secure flag, HttpOnly flag, SameSite policy, domain scoping, and security cookie prefixes (__Host- and __Secure-).
Misconfigured cookies expose users to Cross-Site Scripting (XSS) session theft, Cross-Site Request Forgery (CSRF), and unencrypted wiretapping over non-HTTPS connections.
Makes an unauthenticated HTTP GET request to the target domain, following legitimate redirects.
Parses all returned Set-Cookie response headers into individual attribute key-value pairs.
Checks whether Secure, HttpOnly, and SameSite directives are properly defined.
Assigns an overall cookie posture grade and provides actionable remediation guidance for developers.
| Result / Status | Technical Meaning | Recommended Action |
|---|---|---|
| Optimal Configuration | Secure flag active, HttpOnly active, SameSite=Strict or Lax, and __Host- prefix applied. | Maintain configuration; ensure these flags remain enforced in production frameworks. |
| Missing HttpOnly | Cookie accessible by client-side JavaScript via document.cookie, making session vulnerable to XSS theft. | Add "HttpOnly" attribute to Set-Cookie header on server-side session cookies. |
| Missing Secure Flag | Cookie transmitted in plaintext if a user clicks an unencrypted HTTP link, allowing wiretapping. | Add "Secure" attribute; verify HSTS is enabled to prevent unencrypted requests. |
| SameSite=None without Secure | Cookie sent across third-party contexts and rejected by modern browsers; severe CSRF risk. | Set SameSite=Lax (default) or SameSite=Strict; if None is required, pair with the Secure flag. |
Under RFC 6265bis, cookie prefixes provide cryptographic-like assurances that cannot be overridden by subdomains. A cookie prefixed with __Host- MUST include the Secure flag, MUST NOT include a Domain attribute (scoping it strictly to the origin), and MUST set Path=/.
This neutralizes cookie tossing attacks where a compromised subdomain injects malicious cookies to hijack the parent domain session. When paired with SameSite=Lax or SameSite=Strict, modern cookie architecture provides defense-in-depth against CSRF without relying solely on anti-CSRF tokens.
Verifying that Laravel, Django, Express, or ASP.NET session cookie middlewares enforce security flags in production.
Detecting exposed session identifiers that can be exfiltrated through cross-site scripting vulnerabilities.
Validating that authentication tokens and payment session cookies meet PCI DSS requirement 6.4.
Auditing Nginx, Cloudflare, or AWS ALB cookie rewrites and sticky session configurations.
Maintaining an accurate threat model requires understanding what external point-in-time tools can and cannot evaluate:
Complementary security utilities, audit calculators, and posture generators.
Audit CSP, HSTS, X-Frame-Options, and other defensive HTTP headers.
Prevent XSS attacks from stealing cookies even if HttpOnly is omitted.
Ensure HTTP requests redirect to HTTPS so Secure cookies are never sent in plaintext.
Verify TLS certificate validity and cryptographic handshake security.
This tool operates in direct accordance with verified cybersecurity standards and technical specifications established by authoritative primary institutions:
The authoritative engineering standard defining cookie syntax, attributes, and browser handling.
Technical reference for secure cookie configuration, SameSite semantics, and cookie prefixes.
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