Firefox JIT Vulnerability Exposes Tor Browser Users to Remote Code Execution
A high-severity vulnerability in the JavaScript engine of Firefox can allow remote compromise of the Tor Browser simply by opening a malicious webpage. The flaw affects versions without the latest patches and requires no additional downloads or user permissions.
Tracked as CVE-2026-10702, the issue permits arbitrary code execution inside the browser's content rendering process. Mozilla rated the vulnerability as high severity. The root cause lies in the SpiderMonkey JIT compiler, which converts JavaScript into native code. An incorrect analysis leaves a reference to a memory region that has already been freed, creating an exploitable use-after-free condition.
Researchers showed that the bug grants arbitrary memory read and write capabilities. In the Tor Browser, compromising this process can enable follow-on attacks aimed at identifying the user or targeting the underlying operating system.
The same vulnerability was used as the first stage in the IonStack exploit chain against an ARM64 device running Android 17. When combined with CVE-2026-43499 in the Linux kernel, the attack successfully escalated privileges to root level.
Mozilla fixed the vulnerability in Firefox 151.0.3. The Tor Project incorporated the security updates in Tor Browser 15.0.19, which also updated the bundled Firefox ESR and included backported fixes from newer releases.
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