PatchSiren

PatchSiren cyber security CVE debrief

CVE-2026-74987 Mozilla CVE debrief

AI-assisted PatchSiren debrief based on the supplied source corpus. The CVE record for CVE-2026-74987 was published on 2026-08-18T13:17:40.560Z. This critical vulnerability, with a CVSS score of 9.8, was found in Firefox ESR 140.13, Firefox ESR 153.0, and Firefox 153. The bugs showed evidence of memory corruption or another security-relevant defect, which could potentially be exploited with enough effort. The vulnerability was fixed in Firefox 154, Firefox ESR 140.14, Firefox ESR 153.1, Thunderbird 154, Thunderbird 140.14, and Thunderbird 153.1. Organizations and users of these versions should be aware of this critical vulnerability and take immediate action to update to patched versions.

Vendor
Mozilla
Product
Firefox
CVSS
CRITICAL 9.8
CISA KEV
Not listed in stored evidence
Original CVE published
2026-08-18
Original CVE updated
2026-09-01
Advisory published
2026-08-18
Advisory updated
2026-09-01

Who should care

Organizations and users of Firefox ESR 140.13, Firefox ESR 153.0, and Firefox 153 should be aware of this critical vulnerability and take immediate action to update to patched versions. This includes reviewing and implementing compensating controls for exposed systems while remediation is scheduled and verified, and checking relevant monitoring, detection, and logs for exposed assets that need extra review.

Technical summary

The CVE record indicates that internally found bugs were present in Firefox ESR 140.13, Firefox ESR 153.0, and Firefox 153, showing evidence of memory corruption or another security-relevant defect. These bugs could potentially be exploited with enough effort. The vulnerability was fixed in Firefox 154, Firefox ESR 140.14, Firefox ESR 153.1, Thunderbird 154, Thunderbird 140.14, and Thunderbird 153.1. Affected organizations should prioritize updating to these patched versions to mitigate this vulnerability.

Defensive priority

Organizations using Firefox ESR 140.13, Firefox ESR 153.0, and Firefox 153 should prioritize updating to Firefox 154, Firefox ESR 140.14, Firefox ESR 153.1, Thunderbird 154, Thunderbird 140.14, and Thunderbird 153.1 to mitigate this vulnerability.

Recommended defensive actions

  • Update to Firefox 154, Firefox ESR 140.14, Firefox ESR 153.1, Thunderbird 154, Thunderbird 140.14, and Thunderbird 153.1
  • Inventory checks for Firefox ESR 140.13, Firefox ESR 153.0, and Firefox 153 installations
  • Monitor for potential memory corruption or security-relevant defects
  • Exception tracking for vulnerable versions
  • Retest after updating to patched versions
  • Review compensating controls for exposed systems while remediation is scheduled and verified
  • Check relevant monitoring, detection, and logs for exposed assets that need extra review

Evidence notes

The CVE record indicates that internally found bugs were present in Firefox ESR 140.13, Firefox ESR 153.0, and Firefox 153, showing evidence of memory corruption or another security-relevant defect. The vulnerability was fixed in Firefox 154, Firefox ESR 140.14, Firefox ESR 153.1, Thunderbird 154, Thunderbird 140.14, and Thunderbird 153.1.

Sources and references

Verified primary and authoritative sources

  • CVE-2026-74987 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-74987

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

  • CVE-2026-74987 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-74987

    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.