A use‑after‑free flaw is present in the Navigation component of the DOM in Mozilla Firefox and Thunderbird. If an attacker can trigger it, the flaw can corrupt process memory, possibly allowing arbitrary code execution or a crash that results in data loss or denial of service. The weakness illustrates improper memory management during document navigation.

Mozilla Firefox versions before 156 and the ESR releases 115.41, 140.16, and 153.3 are affected. Mozilla Thunderbird versions before 156 and the ESR releases 140.16 and 153.3 also contain the vulnerability. Any system running these releases without the documented fixes may be vulnerable to exploitation.

The vulnerability has a CVSS score of 8.8, indicating a high potential impact. The EPSS score is below 1 %, indicating very low exploitation probability. It is not listed in CISA’s KEV catalog. Triggering the flaw requires crafted web content that causes a navigation event. The likely attack vector is delivery via email attachments or malicious websites, based on the description, but this is an inference. While the likelihood of exploitation is low, successful exploitation could lead to full process compromise or application denial of service.