Summary
| Parameter | Value |
|---|---|
| CVE ID | CVE-2026-5731 |
| Alert Source | GitHub Advisory - Critical Vulnerability |
| CVE Publication Year | 2026 |
| Date Published | 2026-04-07 |
| Vendor | Mozilla |
| Product | Firefox |
| CVSS Score | 9.8 (critical) |
| EPSS Score | No data |
| CISA KEV | No |
| Ransomware | Not confirmed |
Vulnerability Description
Memory safety bugs present in Firefox ESR 115.34.0, Firefox ESR 140.9.0, Thunderbird ESR 140.9.0, Firefox 149.0.1 and Thunderbird 149.0.1. 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. This vulnerability affects Firefox < 149.0.2, Firefox ESR < 115.34.1, and Firefox ESR < 140.9.1.
Required Actions
Apply vendor patches or mitigations as soon as available.
Who Is Affected?
This vulnerability affects Firefox by Mozilla. Check if your organization uses this software and requires updates.
Sources
Need help securing your systems? nFlo team offers vulnerability management and 24/7 SOC services. Contact us.
How can nFlo help?
If your organization uses products affected by this vulnerability, contact us. We can help with:
- Verifying whether your systems are at risk
- Implementing patches and risk mitigation
- Monitoring for exploitation attempts in your environment
Useful resources:
