Definition
A query string is a URL component that gives values to specific parameters. Typically begins with a question mark (?) and proceeds with pairs of key-value entries. These pairs are separated with an ampersand (&) and within each pair, an equals sign (=) connects the key and the value.
Consider the following URL:
https://www.privacy.com/page?param1=value1¶m2=value2
In this example, ?param1=value1¶m2=value2 is the query string.
Query strings transmit data to the server, enabling tailored responses. For instance, a query string can contain search items, indicate the sorting order of products, or reveal the current page number within a multi-page inventory.
Query String Vulnerabilities
- Information disclosure: Query strings are present in browsers’ address bars, browsing history, bookmarks, and referral logs. So, if the query string contains sensitive data (like authentication tokens, passwords, and personally identifiable information), it can be exposed to anyone with the URL.
- URL length limitations: Servers and browsers limit URL length to around 2000 characters. If the amount of data in the URL exceeds the limit, server errors or truncated data could arise.
- Web server log exposure: Web servers routinely log accessed URLs, including query strings. If sensitive data within the query string is not adequately secured, it could be stored in server logs, potentially becoming a source of data leaks.
- Manipulation: Without validation or sanitization of the query strings, attackers can modify or exploit them and steal sensitive data.
- Inefficient data transmission: Query strings are less efficient for sharing large amounts of data than POST requests, which handle larger payloads well.
- Cross-site scripting (XSS): If web applications fail to properly escape or validate data from query strings before displaying it on the webpage, they can be vulnerable to XSS attacks. Hackers can inject malicious scripts through query parameters implemented in a user’s browser.
- SQL injection: Applications may be vulnerable to SQL injection attacks if they use raw query strings without properly validating and parameterizing them.
- CSRF (Cross-site request forgery): Query strings are not ideal for critical operations as attackers can replicate malicious URLs that, if clicked, can execute unwanted actions on the website on behalf of the victim.