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https://github.com/wikimedia/mediawiki-tools-phan-securitycheckplugin

Mirror of https://gerrit.wikimedia.org/g/mediawiki/tools/phan/SecurityCheckPlugin See https://www.mediawiki.org/wiki/Developer_access for contributing
https://github.com/wikimedia/mediawiki-tools-phan-securitycheckplugin

phan security-audit static-analysis taint-analysis

Last synced: 2 months ago
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Mirror of https://gerrit.wikimedia.org/g/mediawiki/tools/phan/SecurityCheckPlugin See https://www.mediawiki.org/wiki/Developer_access for contributing

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README 

        
Phan Security Check Plugin

===============================



This is a plugin to [Phan] to try and detect security issues

(such as [XSS]). It keeps track of any time a user can modify

a variable, and checks to see that such variables are

escaped before being output as html or used as an sql query, etc.



It supports generic PHP projects, and it also has a dedicated mode

for MediaWiki code (analyzes hooks, HTMLForms and Database methods).



A [web demo] is available.



Usage

-----



### Install



    $ composer require --dev mediawiki/phan-taint-check-plugin



### Usage

The plugin can be used in both "manual" and "standalone" mode. The former is the best

choice if your project is already running phan, and almost no configuration is needed.

The latter should only be used if you don't want to add phan to your project, and is not

supported for MediaWiki-related code. For more information about Wikimedia's use of this

plugin see https://www.mediawiki.org/wiki/Phan-taint-check-plugin.



#### Manual

You simply have to add taint-check to the `plugins` section of your phan config. Assuming

that taint-check is in the standard vendor location, e.g.

` $seccheckPath = 'vendor/mediawiki/phan-taint-check-plugin/';`, the file to include is

`"$seccheckPath/GenericSecurityCheckPlugin.php"` for a generic project, and

`"$seccheckPath/MediaWikiSecurityCheckPlugin.php"` for a MediaWiki project.



Also, make sure that quick mode is disabled, or the plugin won't work:

```php

   'quick_mode' => false

```



You should also add `SecurityCheck-LikelyFalsePositive` and

`SecurityCheck-PHPSerializeInjection` to `suppress_issue_types` (the latter

has a high rate of false positives).



Then run phan as you normally would:



    $ vendor/bin/phan -d . --long-progress-bar



Running phan with `--analyze-twice` will catch additional security issues that

might go unnoticed in the normal analysis phase. A known limitation of this is that

the same issue might be reported more than once with different caused-by lines.



#### Standalone

You can run taint-check via:



    $ ./vendor/bin/seccheck



You might want to add a composer script alias for that:



```json

  "scripts": {

     "seccheck": "seccheck"

  }

```



Note that false positives are disabled by default.



Plugin output

-------------



The plugin will output various issue types depending on what it

detects. The issue types it outputs are:



* `SecurityCheck-XSS`

* `SecurityCheck-SQLInjection`

* `SecurityCheck-ShellInjection`

* `SecurityCheck-PHPSerializeInjection` - For when someone does `unserialize( $_GET['d'] );`

  This issue type seems to have a high false positive rate currently.

* `SecurityCheck-CUSTOM1` - To allow people to have custom taint types

* `SecurityCheck-CUSTOM2` - ditto

* `SecurityCheck-DoubleEscaped` - Detecting that HTML is being double escaped

* `SecurityCheck-RCE` - Remote code execution, e.g. `eval( $_GET['foo'] )`

* `SecurityCheck-PathTraversal` - Path traversal, e.g. `require $_GET['foo']`

* `SecurityCheck-ReDoS` - Regular expression denial of service (ReDoS), e.g. `preg_match( $_GET['foo'], 'foo')`

* `SecurityCheck-LikelyFalsePositive` - A potential issue, but probably not.

  Mostly happens when the plugin gets confused.



The severity field is usually marked as `Issue::SEVERITY_NORMAL (5)`. False

positives get `Issue::SEVERITY_LOW (0)`. Issues that may result in server

compromise (as opposed to just end user compromise) such as shell or sql

injection are marked as `Issue::SEVERITY_CRITICAL (10)`.

SerializationInjection would normally be "critical" but its currently denoted

as a severity of NORMAL because the check seems to have a high false positive

rate at the moment.



You can use the `-y` command line option of Phan to filter by severity.



How to avoid false positives

----------------------------



If you need to suppress a false positive, you can put `@suppress NAME-OF-WARNING`

in the docblock for a function/method. Alternatively, you can use other types of

suppression, like `@phan-suppress-next-line`. See phan's readme for a complete

list.

The `@param-taint` and `@return-taint` (see "Customizing" section) are also very useful

with dealing with false positives.



Note that the plugin will report possible XSS vulnerabilities in CLI context. To avoid them,

you can suppress `SecurityCheck-XSS` file-wide with `@phan-file-suppress` in CLI scripts, or

for the whole application (using the `suppress_issue_types` config option) if the application only

consists of CLI scripts. Alternatively, if all outputting happens from an internal function, you

can use `@param-taint` as follows:

```php

  /**

   * @param-taint $stuffToPrint none

   */

  public function printMyStuff( string $stuffToPrint ) {

    echo $stuffToPrint;

  }

```



When debugging security issues, you can use:

```

'@phan-debug-var-taintedness $varname';

```

this will emit a `SecurityCheckDebugTaintedness` issue containing the taintedness of `$varname`

at the line where the annotation is found. Note that you have to insert the annotation in a string

literal; comments will not work. See also phan's `@phan-debug-var` annotation.



Notable limitations

-------------------

### General limitations



* When an issue is output, the plugin tries to include details about what line

  originally caused the issue. Usually it works, but sometimes it gives

  misleading/wrong information

* The plugin won't recognize things that do custom escaping. If you have

  custom escaping methods, you must add annotations to its docblock so

  that the plugin can recognize it. See the Customizing section.

* Phan does not currently have an API for accessing subclasses for a given class.

  Therefore the SecurityCheckPlugin cannot accommodate certain data flows for

  subclasses that should obviously be considered tainted. The workaround for this

  is to mark any relevant subclass functions as `@return-taint html`.



### MediaWiki specific limitations

* With pass by reference parameters to MediaWiki hooks,

  sometimes the line number is the hook call in MediaWiki core, instead of

  the hook subscriber in the extension that caused the issue.

* The plugin can only validate the fifth (`$options`) and sixth (`$join_cond`)

  of MediaWiki's `IDatabase::select()` if its provided directly as an array

  literal, or directly returned as an array literal from a `getQueryInfo()`

  method.



Customizing

-----------

The plugin supports being customized, by subclassing the [SecurityCheckPlugin]

class. For a complex example of doing so, see [MediaWikiSecurityCheckPlugin].



Sometimes you have methods in your codebase that alter the taint of a

variable. For example, a custom html escaping function should clear the

html taint bit. Similarly, sometimes phan-taint-check can get confused and

you want to override the taint calculated for a specific function.



You can do this by adding a taint directive in a docblock comment. For example:



```php

/**

 * My function description

 *

 * @param string $html the text to be escaped

 * @param-taint $html escapes_html

 */

function escapeHtml( $html ) {

}

```



Methods also inherit these directives from abstract definitions in ancestor interfaces, but not from concrete implementations in ancestor classes.



Taint directives are prefixed with either `@param-taint $parametername` or `@return-taint`. If there are multiple directives they can be separated by a comma. `@param-taint` is used for either marking how taint is transmitted from the parameter to the methods return value, or when used with `exec_` directives, to mark places where parameters are outputted/executed. `@return-taint` is used to adjust the return value's taint regardless of the input parameters.



The type of directives include:

* `exec_$TYPE` - If a parameter is marked as `exec_$TYPE` then feeding that parameter a value with `$TYPE` taint will result in a warning triggered. Typically you would use this when a function that outputs or executes its parameter

* `escapes_$TYPE` - Used for parameters where the function escapes and then returns the parameter. So `escapes_sql` would clear the sql taint bit, but leave other taint bits alone.

* `onlysafefor_$TYPE` - For use in `@return-taint`, marks the return type as safe for a specific `$TYPE` but unsafe for the other types.

* `$TYPE` - if just the type is specified in a parameter, it is bitwised AND with the input variable's taint. Normally you wouldn't want to do this, but can be useful when `$TYPE` is `none` to specify that the parameter is not used to generate the return value. In an `@return` this could be used to enumerate which taint flags the return value has, which is usually only useful when specified as `tainted` to say it has all flags.

* `array_ok` - special purpose flag to say ignore tainted arguments if they are in an array.

* `allow_override` - Special purpose flag to specify that that taint annotation should be overridden by phan-taint-check if it can detect a specific taint.



The value for `$TYPE` can be one of `htmlnoent`, `html`, `sql`, `shell`, `serialize`, `custom1`, `custom2`, `code`, `path`, `regex`, `sql_numkey`, `escaped`, `none`, `tainted`. Most of these are taint categories, except:

* `htmlnoent` - like `html` but disable double escaping detection that gets used with `html`. When `escapes_html` is specified, escaped automatically gets added to `@return`, and `exec_escaped` is added to `@param`. Similarly `onlysafefor_html` is equivalent to `onlysafefor_htmlnoent,escaped`.

* `none` - Means no taint

* `tainted` - Means all taint categories except special categories (equivalent to `SecurityCheckPlugin::YES_TAINT`)

* `escaped` - Is used to mean the value is already escaped (To track double escaping)

* `sql_numkey` - Is fairly special purpose for MediaWiki. It ignores taint in arrays if they are for associative keys.



The default value for `@param-taint` is `tainted` if it's a string (or other dangerous type), and `none` if it's something like an integer. The default value for `@return-taint` is `allow_override` (Which is equivalent to `none` unless something better can be autodetected).



Instead of annotating methods in your codebase, you can also customize

phan-taint-check to have builtin knowledge of method taints. In addition

you can extend the plugin to have fairly arbitrary behaviour.



To do this, you override the `getCustomFuncTaints()` method. This method

returns an associative array of fully qualified method names to an array

describing how the taint of the return value of the function in terms of its

arguments. The numeric keys correspond to the number of an argument, and an

'overall' key adds taint that is not present in any of the arguments.

Basically for each argument, the plugin takes the taint of the argument,

bitwise AND's it to its entry in the array, and then bitwise OR's the overall

key. If any of the keys in the array have an EXEC flags, then an issue is

immediately raised if the corresponding taint is fed the function (For

example, an output function). The EXEC flags don't work in the 'overall' key.



For example, [htmlspecialchars] which removes html taint, escapes its argument and returns the

escaped value would look like:



```php

'htmlspecialchars' => [

	( self::YES_TAINT & ~self::HTML_TAINT ) | self::ESCAPED_EXEC_TAINT,

	'overall' => self::ESCAPED,

];

```



Environment variables

---------------------



The following environment variables affect the plugin. Normally you would not

have to adjust these.



* `SECURITY_CHECK_EXT_PATH` - Path to directory containing

  `extension.json`/`skin.json` when in MediaWiki mode.

  If not set assumes the project root directory.

* `SECCHECK_DEBUG` - File to output extra debug information (If running from

  `shell`, `/dev/stderr` is convenient)



License

-------



[GNU General Public License, version 2 or later]



[web demo]: https://doc.wikimedia.org/mediawiki-tools-phan-SecurityCheckPlugin/master/demos/

[Phan]: https://github.com/phan/phan

[XSS]: https://en.wikipedia.org/wiki/Cross-site_scripting

[SecurityCheckPlugin]: src/SecurityCheckPlugin.php

[MediaWikiSecurityCheckPlugin]: MediaWikiSecurityCheckPlugin.php

[htmlspecialchars]: https://secure.php.net/htmlspecialchars

[GNU General Public License, version 2 or later]: COPYING