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CVE-2026-2758 Mozilla CVE debrief

CVE-2026-2758 is a critical use-after-free vulnerability in the JavaScript: GC component of Mozilla Firefox. The vulnerability was publicly disclosed on February 24, 2026, and was modified on June 30, 2026. It affects multiple versions of Firefox, including Firefox 148, Firefox ESR 115.33, Firefox ESR 140.8, Thunderbird 148, and Thunderbird 140.8. The CVSS score for this vulnerability is 9.8, indicating a critical severity level.

Vendor
Mozilla
Product
Firefox
CVSS
CRITICAL 9.8
CISA KEV
Not listed in stored evidence
Original CVE published
2026-02-24
Original CVE updated
2026-07-15
Advisory published
2026-02-24
Advisory updated
2026-07-15

Who should care

Organizations and individuals using Mozilla Firefox, Firefox ESR, and Thunderbird should prioritize patching this vulnerability to prevent potential exploitation. This vulnerability can be used to execute arbitrary code, potentially leading to system compromise. Users of affected products should update to the latest patched versions as soon as possible.

Technical summary

The CVE-2026-2758 vulnerability is a use-after-free issue in the JavaScript: GC component of Mozilla Firefox. This type of vulnerability occurs when a program attempts to access memory that has already been freed or deleted. An attacker could potentially exploit this vulnerability to execute arbitrary code, allowing for a complete system compromise. The vulnerability has been patched in Firefox 148, Firefox ESR 115.33, Firefox ESR 140.8, Thunderbird 148, and Thunderbird 140.8.

Defensive priority

This vulnerability has a critical CVSS score of 9.8 and can be used for arbitrary code execution, making it a high-priority patch for organizations and individuals using affected Mozilla products.

Recommended defensive actions

  • Apply patches: Update Firefox to version 148, Firefox ESR to version 115.33 or 140.8, and Thunderbird to version 148 or 140.8.
  • Inventory management: Ensure all instances of Firefox, Firefox ESR, and Thunderbird are accounted for and patched.
  • Monitoring: Implement monitoring to detect potential exploitation attempts.
  • Exception tracking: Track and manage exceptions for any compensating controls.
  • Vendor remediation workflow: Engage with Mozilla support for assistance with remediation if needed.

Evidence notes

The CVE-2026-2758 vulnerability was publicly disclosed on February 24, 2026, with a CVSS score of 9.8. Multiple sources, including NVD and Mozilla, have documented this vulnerability. Patches are available in Firefox 148, Firefox ESR 115.33, Firefox ESR 140.8, Thunderbird 148, and Thunderbird 140.8. The vulnerability affects various versions of Firefox and Thunderbird products.

Sources and references

Verified primary and authoritative sources

  • CVE-2026-2758 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-2758

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

  • CVE-2026-2758 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-2758

    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.