# CVE-2026-12301 — Mozilla Firefox

> As of 2026-06-18, CVE-2026-12301 is a MEDIUM-severity vulnerability in Mozilla Firefox, CVSS v3.1 5.3, EPSS 0.2% (15.3th percentile). Threadlinqs Intelligence links 1 tracked threat campaign to CVE-2026-12301, most recently “Multiple Vulnerabilities in Firefox 152 Enable Remote Code Execution and Sandbox Escape (MFSA 2026-57)”.

**Last updated:** 2026-06-18

## What is CVE-2026-12301?

Memory safety bug fixed in Firefox 152. This vulnerability was fixed in Firefox 152 and Thunderbird 152.

The record classifies CVE-2026-12301 under weakness class [CWE-119](https://intel.threadlinqs.com/cwe/CWE-119). Its CVSS v3 base vector states that the flaw is reachable remotely over the network, needs no prior authentication, needs no user interaction. 2 affected-product entries are recorded, across 1 vendor, listed below. The identifier was first published 116 days ago.

## Severity and exploitation probability

- **CVSS v3.1 base score:** 5.3 — MEDIUM (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N`)
- **EPSS (FIRST):** 0.2% probability of exploitation in the next 30 days, higher than 15.3% of all scored CVEs
- **CISA KEV:** Not listed in the CISA Known Exploited Vulnerabilities catalog
- **Threadlinqs priority:** 3.3/10 — a Threadlinqs composite of the CVSS base score, the EPSS percentile and public exploit availability
- **Published:** 2026-06-16, last modified 2026-06-18

## Is CVE-2026-12301 being exploited?

It currently carries a trending score of 10 in the Threadlinqs vulnerability feed.

## Affected products and versions

- [Mozilla](https://intel.threadlinqs.com/vendors/mozilla): Firefox, Thunderbird

## How to fix CVE-2026-12301

Vendor advisory: [https://www.mozilla.org/security/advisories/mfsa2026-57/](https://www.mozilla.org/security/advisories/mfsa2026-57/). Apply the vendor fix referenced above to every affected product listed in this record, then confirm the running version against the vendor advisory.

## Threat activity tracking CVE-2026-12301

1 tracked threat in the Threadlinqs corpus references CVE-2026-12301, either in the campaign’s CVE list or as an indicator on the campaign record.

- [Multiple Vulnerabilities in Firefox 152 Enable Remote Code Execution and Sandbox Escape (MFSA 2026-57)](https://intel.threadlinqs.com/threat/TL-2026-0855) — HIGH · 2026-06-18

## Sources

Enriched from CVE.org, NVD, FIRST EPSS. Last verified by Threadlinqs on 2026-10-10. This product uses the NVD API but is not endorsed or certified by the NVD.

**Other references**

- [bugzilla.mozilla.org](https://bugzilla.mozilla.org/show_bug.cgi?id=2015647)
- [mozilla.org](https://www.mozilla.org/security/advisories/mfsa2026-57/)
- [mozilla.org (mfsa2026 60)](https://www.mozilla.org/security/advisories/mfsa2026-60/)

Canonical: https://intel.threadlinqs.com/cve/CVE-2026-12301
Full detection coverage and IOCs for threats exploiting CVE-2026-12301 via the Threadlinqs MCP server (Purple tier): https://intel.threadlinqs.com/mcp