Description
The software uses a cookie to store sensitive information, but the cookie is not marked with the HttpOnly flag.
The HttpOnly flag directs compatible browsers to prevent client-side script from accessing cookies. Including the HttpOnly flag in the Set-Cookie HTTP response header helps mitigate the risk associated with Cross-Site Scripting (XSS) where an attacker’s script code might attempt to read the contents of a cookie and exfiltrate information obtained. When set, browsers that support the flag will not reveal the contents of the cookie to a third party via client-side script executed via XSS.
An HTTP cookie is a small piece of data attributed to a specific website and stored on the user’s computer by the user’s web browser. This data can be leveraged for a variety of purposes including saving information entered into form fields, recording user activity, and for authentication purposes. Cookies used to save or record information generated by the user are accessed and modified by script code embedded in a web page. While cookies used for authentication are created by the website’s server and sent to the user to be attached to future requests. These authentication cookies are often not meant to be accessed by the web page sent to the user, and are instead just supposed to be attached to future requests to verify authentication details.
Modes of Introduction:
– Implementation
Likelihood of Exploit: Medium
Related Weaknesses
Consequences
Confidentiality: Read Application Data
If the HttpOnly flag is not set, then sensitive information stored in the cookie may be exposed to unintended parties.
Integrity: Gain Privileges or Assume Identity
If the cookie in question is an authentication cookie, then not setting the HttpOnly flag may allow an adversary to steal authentication data (e.g., a session ID) and assume the identity of the user.
Potential Mitigations
Phase: Implementation
Effectiveness: High
Description:
Leverage the HttpOnly flag when setting a sensitive cookie in a response.
While this mitigation is effective for protecting cookies from a browser’s own scripting engine, third-party components or plugins may have their own engines that allow access to cookies. Attackers might also be able to use XMLHTTPResponse to read the headers directly and obtain the cookie.
CVE References
- CVE-2014-3852
- CMS written in Python does not include the HTTPOnly flag in a Set-Cookie header, allowing remote attackers to obtain potentially sensitive information via script access to this cookie.
- CVE-2015-4138
- Appliance for managing encrypted communications does not use HttpOnly flag.