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Barracuda Web Application Firewall

How to Secure HTTP Cookies

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Overview

Cookies provide a mechanism to store session state information on client navigation platforms such as browsers and other user agents. Cookies can store user preferences or shopping cart items, and can include sensitive information like registration or login credentials. If a cookie can be modified, the system can become vulnerable to attacks and sensitive information can be stolen.

How Cookie Security Works

The Barracuda Web Application Firewall cookie security is transparent to back-end servers. When a server inserts a cookie, the Barracuda Web Application Firewall intercepts the response and encrypts or signs the cookie before delivering it to the client. When a subsequent request from the client returns this cookie, the Barracuda Web Application Firewall intercepts the request and decrypts it or verifies its signature. If the cookie is unaltered, the Barracuda Web Application Firewall forwards the original cookie to the server. Altered cookies are removed before the Barracuda Web Application Firewall forwards the request to the server.

Encryption prevents both viewing and tampering with cookies, so it prevents the client from accessing cookie values. For clients who need to access cookie values, use signing to allow it. When signing cookies, the Barracuda Web Application Firewall actually forwards two cookies to the client browser, one plain text cookie and one signed cookie. When a subsequent request from the client returns the cookies, if either cookie is altered, signature verification fails, and the Barracuda Web Application Firewall removes cookies before forwarding the request to the server.

Cookie Security Interaction With Other Security Features

Encrypting a cookie may change the length of the cookie, but the number of headers in the message remains unchanged. When a cookie is signed, the length of the cookie changes and one or more headers is appended to the forwarded message. If the SECURITY POLICIES > Request Limits configuration specifies constraints on the number or length of HTTP headers, a signed or encrypted cookie may violate the request limits and result in unwanted rejection of messages. Messages thus rejected are logged as Cloak under Action on the BASIC > Web Firewall Logs page.

Configuring Cookie Security

To encrypt or sign cookies and reject tampered cookies, you need to enable cookie security using the following steps:

  1. Go to the SECURITY POLICIES > Cookie Security page.
  2. Select a policy from the Policy Name list.
  3. In the Cookie Security section, select the desired Tamper Proof Mode, either Encrypted or Signed. Recommended: Signed. Note: Encrypting cookie data makes cookie values inaccessible to the client. If required, change values of other parameter(s):
    • Cookie Max Age – Enter the maximum age in minutes for session cookies after which cookies are automatically expired.
      • Range: 0 to 500000
      • Recommended: 1440
      • Units: Minutes
    • Cookie Replay Protection Type – Select the type of protection to be used to prevent cookie replay attacks from the drop-down list.
      • Values: Custom Headers, IP, IP and Custom Headers, None
      • Recommended: IP
    • Custom Headers – Enter the custom headers to be used in the cookie if the parameter Cookie Replay Protection Type is set to Custom Headers or IP and Custom Headers and click Add.
    • Secure Cookie – Set to Yes to allow cookies to be returned to the web server if the client makes secure HTTPS connection only.
      • Values: Yes, No
      • Recommended: No
    • HTTP Only – Set to Yes to allow cookies to be returned to the web server only if the client makes an HTTP connection. When a client-side script attempts to read a cookie with HTTP Only enabled, the browser returns an empty string as the result. Enabling HTTP Only prevents the cookie from being accessed through client-side scripts.
      • Values: Yes, No
      • Recommended: No
    • Allow Unrecognized Cookies – Select whether unrecognized cookies should be allowed. Use Custom to temporarily allow unrecognized cookies after deploying. Use Days Allowed to indicate for how long unrecognized cookies are allowed.
      • Values - Always, Never, Custom
      • Default - Custom
    • Days Allowed – Enter the number of days unrecognized cookies will not be rejected. This field is used only when Allow Unrecognized Cookies is Custom.
    • Cookies Exempted – Add the names of cookies to exempt from the cookie security policy.
  4. Click Save.
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