An integer overflow and subsequent use‑after‑free occur in the Graphics: Text component. The overflow happens during text rendering data processing and can lead to heap memory corruption, which may be exploited for arbitrary code execution or service disruption.

Mozilla Firefox versions earlier than 159 and Mozilla Thunderbird versions earlier than 159 are affected. The issue is fixed in Firefox 159 and all releases that follow, as well as in Thunderbird 159 and later.

The CVSS score is not provided and the EPSS score is unavailable. The vulnerability is not listed in the CISA KEV catalog, indicating no known public exploits at the time of analysis. Nevertheless, the potential for heap memory corruption warrants urgent attention. The likely attack vector would involve rendering text that triggers the overflow, although the specific trigger conditions are not detailed in the available data.