# CVE-2026-12327 — Mozilla Firefox

> As of 2026-06-17, CVE-2026-12327 is a HIGH-severity vulnerability in Mozilla Firefox, CVSS v3.1 8.1, EPSS 0.4% (32.8th percentile). Threadlinqs Intelligence links 1 tracked threat campaign to CVE-2026-12327, most recently “Multiple Vulnerabilities in Firefox 152 Enable Remote Code Execution and Sandbox Escape (MFSA 2026-57)”.

**Last updated:** 2026-06-17

## What is CVE-2026-12327?

Memory safety bugs present in Firefox ESR 140.11, Thunderbird ESR 140.11, Firefox 151 and Thunderbird 151. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code. This vulnerability was fixed in Firefox 152, Firefox ESR 140.12, Thunderbird 152, and Thunderbird 140.12.

The record classifies CVE-2026-12327 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, and has high impact on confidentiality, integrity, availability. 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:** 8.1 — HIGH (`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **EPSS (FIRST):** 0.4% probability of exploitation in the next 30 days, higher than 32.8% of all scored CVEs
- **CISA KEV:** Not listed in the CISA Known Exploited Vulnerabilities catalog
- **Threadlinqs priority:** 5.4/10 — a Threadlinqs composite of the CVSS base score, the EPSS percentile and public exploit availability
- **Published:** 2026-06-16, last modified 2026-06-17

## Is CVE-2026-12327 being exploited?

It currently carries a trending score of 14 in the Threadlinqs vulnerability feed.

## Affected products and versions

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

## How to fix CVE-2026-12327

No vendor patch reference has been recorded for CVE-2026-12327 in the tracked sources. Follow the references below for a fix, and treat the products listed above as exposed until the vendor states otherwise.

## Threat activity tracking CVE-2026-12327

1 tracked threat in the Threadlinqs corpus references CVE-2026-12327, 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, FIRST EPSS. Last verified by Threadlinqs on 2026-10-10.

**Other references**

- [bugzilla.mozilla.org](https://bugzilla.mozilla.org/buglist.cgi?bug_id=2011842%2C2023902%2C2025512%2C2027312%2C2029444%2C2036571%2C2036900%2C2036936%2C2037995%2C2038551%2C2040717%2C2042724)
- [mozilla.org](https://www.mozilla.org/security/advisories/mfsa2026-57/)
- [mozilla.org (mfsa2026 58)](https://www.mozilla.org/security/advisories/mfsa2026-58/)
- [mozilla.org (mfsa2026 60)](https://www.mozilla.org/security/advisories/mfsa2026-60/)
- [mozilla.org (mfsa2026 61)](https://www.mozilla.org/security/advisories/mfsa2026-61/)

Canonical: https://intel.threadlinqs.com/cve/CVE-2026-12327
Full detection coverage and IOCs for threats exploiting CVE-2026-12327 via the Threadlinqs MCP server (Purple tier): https://intel.threadlinqs.com/mcp