Memory safety bugs were identified that could corrupt internal data structures in Mozilla Firefox and Thunderbird. The issue can lead to undefined behaviour; the special circumstances required for exploitation are complex, but the developer advisory states that, with sufficient effort, an attacker could potentially run arbitrary code. The severity is reflected in a CVSS score of 9.8, indicating a critical level of impact on confidentiality, integrity, and availability of affected systems.

Versions of Firefox ESRS 115.x or 140.x and Firefox 148, as well as Thunderbird ESRS 140.x and Thunderbird 148, are subject to the vulnerability. The defect was corrected in Firefox 149, Firefox ESR 115.34, Firefox ESR 140.9, Thunderbird 149, and Thunderbird ESR 140.9. Any system that remains on the earlier releases retains the risk.

With a CVSS score of 9.8 the threat is severe, yet the exploit probability reported by EPSS is less than 1 %, suggesting attacks are unlikely at present. The vulnerability is not included in the CISA Known Exploited Vulnerabilities catalog. Attacks would likely involve delivering malicious web pages or email content that triggers the memory corruption, potentially allowing code execution if an attacker has the required level of access to a vulnerable client. This inference is based on the nature of memory corruption in a browser or mail client and the information in the advisory.