Authentication / Cookie Variable Exposed

Web and API


Cookie Variable Exposed is a type of vulnerability commonly found in web and API applications. It occurs when data stored in a cookie is made available to an unauthorized user, allowing them to gain access to the application or system. This vulnerability is classified as an Authentication vulnerability in the Common Weakness Enumeration (CWE) directory, and is further discussed in the OWASP Testing Guide.


This vulnerability poses a great risk to organizations and users, as it can lead to unauthorized access to applications and systems. If exploited, this vulnerability can allow attackers to access confidential information, and even gain full control of a system. It is important for organizations to assess the risk posed by this vulnerability and take appropriate steps to mitigate it.


The best way to prevent this vulnerability is to ensure that all cookies are encrypted and decrypted only when needed. Additionally, it is important to ensure that cookies do not contain sensitive information such as usernames, passwords, or other authentication credentials. It is also important to regularly review cookies and validate their contents to ensure that they do not contain any sensitive data.


The following code example is taken from CVE-2020-25108 and describes an example of Cookie Variable Exposed vulnerability.

  function vulnerable (user_id) {
    document.cookie = “user_id=”+user_id;
    <input type="text" name="user_id" />
    <input type="submit" onclick="vulnerable(document.forms[0].user_id.value)" />

In this example, the vulnerable function is used to store the user_id in a cookie. This data can then be accessed by an unauthorized user, allowing them to gain access to the application or system.

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