Package Instance

XWiki Platform remote code execution from account via custom skins support
### Impact
Any user who can edit any page like their profile can create a custom skin with a template override that is executed with programming right, thus allowing remote code execution. 

To reproduce, as a user without edit, script or admin right, add an object of class `XWiki.XWikiSkins` to your profile. Name it whatever you want and set the Base Skin to `flamingo`.
Add an object of class `XWikiSkinFileOverrideClass` and set the path to `macros.vm` and the content to:
```
#macro(mediumUserAvatar $username)
  #resizedUserAvatar($username 50)
  $services.logging.getLogger('Skin').error("I got programming: $services.security.authorization.hasAccess('programming')")
#end
```
Back to your profile, click `Test this skin`. Force a refresh, just in case.
If the error "Skin - I got programming: true" gets logged, the installation is vulnerable.

### Patches
This has been patched in XWiki 14.10.19, 15.5.4 and 15.10RC1.

### Workarounds
We're not aware of any workaround except upgrading.

### References
* https://jira.xwiki.org/browse/XWIKI-21478
* https://github.com/xwiki/xwiki-platform/commit/3d4dbb41f52d1a6e39835cfb1695ca6668605a39 (>= 15.8 RC1)
* https://github.com/xwiki/xwiki-platform/commit/da177c3c972e797d92c1a31e278f946012c41b56 (< 15.8 RC1)

XWiki Platform: Privilege escalation (PR) from user registration through PDFClass
### Impact
Remote code execution is possible via PDF export templates.
To reproduce on an installation, register a new user account with username `PDFClass` if `XWiki.PDFClass` does not exist.
On `XWiki.PDFClass`, use the class editor to add a "style" property of type "TextArea" and content type "Plain Text".
Then, add an object of class `PDFClass` and set the "style" attribute to `$services.logging.getLogger('PDFClass').error("I got programming: $services.security.authorization.hasAccess('programming')")`.
Finally, go to `<host>/xwiki/bin/export/Main/WebHome?format=pdf&pdftemplate=XWiki.PDFClass`. If the logs contain "ERROR PDFClass - I got programming: true", the instance is vulnerable.

### Patches
This vulnerability has been patched in XWiki 14.10.20, 15.5.4 and 15.10-rc-1.

### Workarounds
If PDF templates are not typically used on the instance, an administrator can create the document `XWiki.PDFClass` and block its edition, after making sure that it does not contain a `style` attribute.
Otherwise, the instance needs to be updated.

### References
- https://jira.xwiki.org/browse/XWIKI-21337
- https://github.com/xwiki/xwiki-platform/commit/d28e21a670c69880b951e415dd2ddd69d273eae9