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CVE-2026-92040 Mozilla CVE debrief

A use-after-free vulnerability in the JavaScript: WebAssembly component of Firefox and Thunderbird has been patched. This issue, CVE-2026-92040, was fixed in Firefox 156 and Thunderbird 156. The vulnerability has a CVSS score of 8.8 and is considered HIGH severity. The vulnerability affects the WebAssembly component, which is used in Firefox and Thunderbird, and could potentially lead to crashes or code execution. Defenders should prioritize verifying exposure in their Firefox and Thunderbird deployments, especially if they use WebAssembly components in their applications. Verification of exposure and updating to patched versions can prevent potential exploitation. Reviewing WebAss

Vendor
Mozilla
Product
Firefox
CVSS
HIGH 8.8
CISA KEV
Not listed in stored evidence
Original CVE published
2026-09-15
Original CVE updated
2026-09-20
Advisory published
2026-09-15
Advisory updated
2026-09-20

Who should care

Defenders responsible for Firefox and Thunderbird deployments, especially those using WebAssembly components, should assess their exposure to this vulnerability and prioritize updates to patched versions.

Why it matters

CVE-2026-92040 is a HIGH-severity use-after-free vulnerability in the JavaScript: WebAssembly component of Firefox and Thunderbird. Defenders should prioritize verifying exposure and updating to patched versions to prevent potential exploitation.

  • Verification of exposure in Firefox and Thunderbird deployments is necessary to prevent potential crashes or code execution.
  • Updating to patched versions of Firefox and Thunderbird can prevent potential exploitation of this vulnerability.
  • Defenders should review WebAssembly component usage in applications to assess potential impact and prioritize updates accordingly.

Technical summary

The CVE-2026-92040 vulnerability is a use-after-free issue in the JavaScript: WebAssembly component of Firefox and Thunderbird. This vulnerability was patched in Firefox 156 and Thunderbird 156. The CVSS score for this vulnerability is 8.8, indicating a HIGH severity level.

Defensive priority

Defenders should prioritize verifying exposure in their Firefox and Thunderbird deployments, especially if they use WebAssembly components in their applications.

Recommended defensive actions

  • Verify Firefox and Thunderbird deployments for exposure, especially those using WebAssembly components.
  • Update Firefox to version 156 or later and Thunderbird to version 156 or later.
  • Review WebAssembly component usage in applications and assess potential impact.

Evidence notes

The CVE record and NVD entry provide details on the vulnerability, including its CVSS score and patched versions. However, further verification is needed to determine the full scope of affected systems and potential impact.

Sources and references

Verified primary and authoritative sources

  • CVE-2026-92040 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-92040

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

  • CVE-2026-92040 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-92040

    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.