Summary
A stored XSS vulnerability in Excalidraw's web embeddable component. This allows arbitrary JavaScript to be run in the context of the domain where the editor is hosted.
Poc
Inserting an embed with the below url (can be copy/pasted onto canvas to insert as embed) will log 42
to the console:
https://gist.github.com/vv=v<script>console.log(42)</script>
Details
There were two vectors. One rendering untrusted string as iframe's srcdoc
without properly sanitizing against HTML injection. Second by improperly sanitizing against attribute HTML injection. This in conjunction with allowing allow-same-origin
sandbox flag (necessary for several embeds) resulted in the XSS.
Former was fixed by no longer rendering unsafe srcdoc
content verbatim, and instead strictly parsing the supplied content and constructing the srcdoc
manually. The latter by sanitizing properly.
The allow-same-origin
flag is now also set only in cases that require it, following the principle of least privilege.
Impact
This is a cross site scripting vulnerability, for more information, please see: https://portswigger.net/web-security/cross-site-scripting
Two npm @excalidraw/excalidraw
stable version releases were affected (0.16.x
, 0.17.x
), and both are now patched.
Summary
A stored XSS vulnerability in Excalidraw's web embeddable component. This allows arbitrary JavaScript to be run in the context of the domain where the editor is hosted.
Poc
Inserting an embed with the below url (can be copy/pasted onto canvas to insert as embed) will log
42
to the console:Details
There were two vectors. One rendering untrusted string as iframe's
srcdoc
without properly sanitizing against HTML injection. Second by improperly sanitizing against attribute HTML injection. This in conjunction with allowingallow-same-origin
sandbox flag (necessary for several embeds) resulted in the XSS.Former was fixed by no longer rendering unsafe
srcdoc
content verbatim, and instead strictly parsing the supplied content and constructing thesrcdoc
manually. The latter by sanitizing properly.The
allow-same-origin
flag is now also set only in cases that require it, following the principle of least privilege.Impact
This is a cross site scripting vulnerability, for more information, please see: https://portswigger.net/web-security/cross-site-scripting
Two npm
@excalidraw/excalidraw
stable version releases were affected (0.16.x
,0.17.x
), and both are now patched.