### [CVE-2021-4140](https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-4140)
![](https://img.shields.io/static/v1?label=Product&message=Firefox%20ESR&color=blue)
![](https://img.shields.io/static/v1?label=Product&message=Firefox&color=blue)
![](https://img.shields.io/static/v1?label=Product&message=Thunderbird&color=blue)
![](https://img.shields.io/static/v1?label=Version&message=%3C%2091.5%20&color=brighgreen)
![](https://img.shields.io/static/v1?label=Version&message=%3C%2096%20&color=brighgreen)
![](https://img.shields.io/static/v1?label=Vulnerability&message=Iframe%20sandbox%20bypass%20with%20XSLT&color=brighgreen)

### Description

It was possible to construct specific XSLT markup that would be able to bypass an iframe sandbox. This vulnerability affects Firefox ESR < 91.5, Firefox < 96, and Thunderbird < 91.5.

### POC

#### Reference
No PoCs from references.

#### Github
- https://github.com/ARPSyndicate/cvemon