CVE-2026-4721
Modified
Modified - Updated After Analysis
Memory Corruption in Firefox and Thunderbird Enables Code Execution
Vulnerability report for CVE-2026-4721, including description, CVSS score, EPSS score, affected products, exploitability, helpful resources, and attack-flow context.
Publication date: 2026-03-24
Last updated on: 2026-06-30
Assigner: Mozilla Corporation
Description
Description
Memory safety bugs present in Firefox ESR 115.33, Firefox ESR 140.8, Thunderbird ESR 140.8, Firefox 148 and Thunderbird 148. 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 was fixed in Firefox 149, Firefox ESR 115.34, Firefox ESR 140.9, Thunderbird 149, and Thunderbird 140.9.
CVSS Scores
EPSS Scores
| Probability: | |
| Percentile: |
Meta Information
Affected Vendors & Products
| Vendor | Product | Version / Range |
|---|---|---|
| mozilla | firefox | to 149.0 (exc) |
| mozilla | firefox | to 115.34.0 (exc) |
| mozilla | firefox | From 128.0 (inc) to 140.9.0 (exc) |
| mozilla | thunderbird | to 149.0 (exc) |
| mozilla | thunderbird | to 140.9.0 (exc) |
Helpful Resources
Exploitability
CWE
KEV
| CWE ID | Description |
|---|---|
| CWE-825 | The product dereferences a pointer that contains a location for memory that was previously valid, but is no longer valid. |
| CWE-120 | The product copies an input buffer to an output buffer without verifying that the size of the input buffer is less than the size of the output buffer. |
