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PatchSiren cyber security CVE debrief

CVE-2026-12327 Mozilla CVE debrief

A memory safety issue was discovered in Firefox ESR 140.11, Thunderbird ESR 140.11, Firefox 151, and Thunderbird 151. The issue, tracked as CVE-2026-12327, was found to have evidence of memory corruption. It is presumed that with sufficient effort, some of these bugs could have been exploited to run arbitrary code. The vulnerability was fixed in Firefox 152 and Firefox ESR 140.12.

Vendor
Mozilla
Product
Firefox
CVSS
HIGH 8.1
CISA KEV
Not listed in stored evidence
Original CVE published
2026-06-16
Original CVE updated
2026-06-17
Advisory published
2026-06-16
Advisory updated
2026-06-17

Who should care

Users of Firefox ESR 140.11, Thunderbird ESR 140.11, Firefox 151, and Thunderbird 151 should update to the latest versions to mitigate this vulnerability.

Technical summary

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.

Defensive priority

high

Recommended defensive actions

  • Update Firefox to version 152 or later.
  • Update Firefox ESR to version 140.12 or later.
  • Update Thunderbird to version 152 or later.
  • Update Thunderbird ESR to version 140.12 or later.

Evidence notes

The CVE record indicates that the vulnerability was fixed in Firefox 152 and Firefox ESR 140.12.

Sources and references

Verified primary and authoritative sources

  • CVE-2026-12327 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-12327

    CVE Program - Official CVE Program record with source-provided CVE metadata.

  • CVE-2026-12327 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-12327

    NIST National Vulnerability Database - Official NIST NVD detail page and source-specific vulnerability assessment.

Supplemental references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.