Mozilla fixed three critical vulnerabilities when it released Firefox 55 on Tuesday, including bugs that could have triggered a crash of the browser and allowed for the execution of arbitrary code.
The code execution vulnerability stems from an XUL injection vulnerability due to improper sanitization of the web page source code. XUL, or XML User Interface Language, is Mozilla’s language for building app interfaces. Frederik Braun, a Berlin-based security engineer for Mozilla who found the vulnerability, cautions the bug could allow for code execution if a user opened a malicious page with the browser’s style editor developer tool
The other two critical bugs, use-after-free vulnerabilities, could have led to exploitable crashes.