SSRF Bypass Techniques: A Comprehensive Guide for Security Researchers

Server-Side Request Forgery (SSRF) vulnerabilities pose a significant threat to web applications, allowing attackers to manipulate server-side requests and potentially access internal systems or resources. However, understanding and effectively mitigating SSRF risks can be challenging. In this blog post, we’ll delve into SSRF bypass techniques and provide a detailed list of URLs for localhost (127.0.0.1) that researchers can leverage for testing and analysis.

SSRF occurs when an attacker tricks a server into making unintended HTTP requests to internal or external systems. This can lead to various exploits, including accessing sensitive data, executing arbitrary code, or bypassing security controls.

Security researchers continually develop innovative methods to bypass SSRF protections. Here are some common techniques:

IP Address Formats:
Leveraging different IP address representations, such as decimal, hexadecimal, and octal formats, can bypass filters and access localhost.

For example:
— http://127.1/
— http://0000::1:80/
— http://[::]:80/
— http://2130706433/
— http://0x7f000001/
— http://017700000001

Unicode Encoding:
— Using Unicode characters to represent IP addresses can evade detection mechanisms. For instance:
— http://⑯⑨。②⑤④。⑯⑨｡②⑤④/
— http://⓪ⓧⓐ⑨｡⓪ⓧⓕⓔ｡⓪ⓧⓐ⑨｡⓪ⓧⓕⓔ:80/

Domain Name Resolution:
Exploiting domain name resolution techniques can trick the server into resolving localhost to a valid domain. For example:
— localtest.me
— http://newyork.localtest.me
— http://mysite.localtest.me

Alternative Representation:
Using unconventional representations of IP addresses or domain names can bypass filters. For instance:
— http://0xd8.0x3a.0xd6.0xe3
— http://0330.072.0326.0343
— http://bugbounty.dod.network

Special Cases:
— Some cases involve unique scenarios or quirks in parsing, such as:
— http://redirecttest.localtest.me
— sub1.sub2.sub3.localtest.me
— http://spoofed.burpcollaborator.net

SSRF vulnerabilities remain a significant concern for web application security. Security researchers play a crucial role in identifying and mitigating these risks. By understanding SSRF bypass techniques and leveraging comprehensive testing strategies, organizations can enhance their security posture and protect against potential exploits. The provided list of localhost URLs serves as a valuable resource for researchers to conduct thorough SSRF assessments and contribute to the advancement of web security.

With this guide and the included SSRF bypass list, researchers can enhance their understanding and effectively identify SSRF vulnerabilities in web applications, ultimately contributing to a safer online environment.

Remember, responsible disclosure is key. Always report vulnerabilities to the appropriate authorities or organizations to ensure timely mitigation and protect users’ data and privacy. Happy hunting!