CVE-2026-16368
A flaw in Firefox and Thunderbird’s WebAssembly handling could let attackers run arbitrary code or crash the browser. The issue was fixed in Firefox 153, Firefox ESR 140.13, Thunderbird 153, and Thunderbird 140.13.
An official fix is available, so this entry is kept for 30 days and then removed automatically.
Who is affected
Firefox and Thunderbird users running versions older than 153 (or ESR 140.13) are affected. Typical users include anyone browsing the web or using Thunderbird for email.
Real-world impact
An attacker could exploit the bug to execute malicious code on a victim’s machine or cause the browser or email client to crash, potentially leading to data loss or further compromise.
Why this severity
The CVSS score of 9.8 reflects that the vulnerability can be exploited remotely without authentication, requires no user interaction, and compromises confidentiality, integrity, and availability of the affected system.
What to do about it
- 01Upgrade Firefox to version 153 or later, or to the ESR 140.13 release or newer.
- 02Upgrade Thunderbird to version 153 or later, or to the ESR 140.13 release or newer.
- 03Restart the browser or email client to complete the update.
NVD-referenced vendor advisory
Timeline
- Jul 21, 2026 · 12d agoPublishedDisclosed and added to the National Vulnerability Database.
- Jul 23, 2026 · 10d agoOfficial fix availableA vendor patch or mitigation now exists — see the remediation steps above.
- Jul 24, 2026 · 9d agoAdvisory updatedThe NVD record was last revised.
How it’s attacked
References & advisories
- bugzilla.mozilla.org/show_bug.cgipermissions required
- mozilla.org/security/advisories/mfsa202…vendor advisory
- mozilla.org/security/advisories/mfsa202…vendor advisory
- mozilla.org/security/advisories/mfsa202…vendor advisory
- mozilla.org/security/advisories/mfsa202…vendor advisory