JIT miscompilation is a flaw in Mozilla’s JavaScript engine that causes the compiler to generate incorrect machine instructions when executing JavaScript code, a defect that can lead to memory corruption or arbitrary code execution within the vulnerable process. The vulnerability is categorized under CWE‑670 (Improper Handling of Exceptions), CWE‑733 (Incomplete Validation/Filtering of Reference to a Resource), and CWE‑843 (Improper Handling of Type Confusion).

Mozilla’s Firefox and Thunderbird browsers are affected; all releases before version 153 are susceptible while releases 153 and later contain the fix.

The EPSS score indicates a very low likelihood of exploitation (<1%). The CVSS score of 9.1 reflects high severity, meaning that a successful exploit could give an attacker full control of the vulnerable process. Based on the description, it is inferred that the likely attack vector is malicious JavaScript, as deduced from the nature of JIT compilation and typical exploitation pathways for similar bugs: a remote attacker could deliver crafted code through a web page or email attachment. The vulnerability is not listed in the CISA KEV catalog.