---
description: Content Security Policy Bypass
---

# CSP Bypass

### <mark style="color:yellow;">Content Security Policy (CSP)</mark>

A special HTTP header is used to mitigate certain types of attacks such as cross-site scripting (XSS).

* **If set up improperly,** it introduces misconfigurations and allows attackers to completely bypass the CSP.

**CSP header value**&#x20;

* made up of directives separated with a semicolon “;”

#### Some CSP Directives <a href="#detailed-csp-directives" id="detailed-csp-directives"></a>

<table><thead><tr><th width="224">Value</th><th>Description</th></tr></thead><tbody><tr><td>Script-src</td><td>describes where we can load javascript files from.</td></tr><tr><td>Default-src</td><td>acts as a catchall for everything else.</td></tr><tr><td>Media-src</td><td>describes where we can load audio and video files from.</td></tr><tr><td>frame-ancestors</td><td>describes which sites can load this site in an iframe.</td></tr><tr><td>Style-src</td><td>describes where we can load stylesheets from.</td></tr></tbody></table>

#### Special Directive Sources <a href="#special-directive-sources" id="special-directive-sources"></a>

<table><thead><tr><th width="226">Value</th><th>Description</th></tr></thead><tbody><tr><td>'none'</td><td>No URLs match.</td></tr><tr><td>'self'</td><td>Refers to the origin site with the same scheme and port number.</td></tr><tr><td>'unsafe-inline'</td><td><p>Allows the usage of inline scripts or styles.         </p><p>EX: (onclick, tags, javascript:,)</p></td></tr><tr><td>'unsafe-eval'</td><td>Allows the usage of eval in scripts.</td></tr><tr><td>sth.ex.com</td><td>Only load resources from specified domain</td></tr></tbody></table>

#### Structure of a CSP header Example

```html
Content-Security-Policy: default-src 'none'; script-src 'self'; connect-src 'self'; img-src 'self'; style-src 'self'; frame-ancestors 'self'; form-action 'self';
```

### <mark style="color:yellow;">Ways to bypass CSP</mark>

💡[LOOK HERE](https://www.cobalt.io/blog/csp-and-bypasses)&#x20;

#### 1. Basic CSP Bypass

💡Always look out for wildcard permissions.

CSP header:

* Content-Security-Policy: script-src 'self' https://cobalt.io https: data \*;

XSS payload:

* \<script src="data:text/javascript,alert(document.domain)">\</script>

#### 2. JSONP CSP Bypass

JSONP is a way to bypass the same object policy (SOP).

A JSONP endpoint lets you insert a javascript payload, normally in a GET parameter called “callback” allowing it to bypass the SOP.

CSP header:

* script-src https://www.google.com [https://accounts.google.com](https://accounts.google.com/);

XSS payload:

* test.com?vuln\_param=https://accounts.google.com/o/oauth2/revoke<mark style="color:green;">?callback=alert(1)</mark>

<figure><img src="https://509923538-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FJ2ZeCCTH4XZTY31hlbGx%2Fuploads%2FTusiH1K8Vu3mKoNluQ7P%2Fimage.png?alt=media&#x26;token=b810103f-b882-49a9-83e3-d93ceda81cf3" alt=""><figcaption><p>alert function being displayed on the page</p></figcaption></figure>

#### 3. CSP Injection Bypass

If our input is reflected in the CSP header, we can control what value the script-src value is set to by setting it to a domain we control.

CSP header:

* script-src <mark style="color:green;">payload</mark>;

