CVE-2026-4720

Description

Memory safety bugs present in 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 140.9, Thunderbird 149, and Thunderbird 140.9.

CVSS Details

CVSS Score

9.8

Severity

CRITICAL

CVSS Vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Configurations (Affected Products)

cpe:2.3:a:mozilla:firefox:*:*:*:*:esr:*:*:* - VULNERABLE

cpe:2.3:a:mozilla:firefox:*:*:*:*:-:*:*:* - VULNERABLE

cpe:2.3:a:mozilla:thunderbird:*:*:*:*:esr:*:*:* - VULNERABLE

cpe:2.3:a:mozilla:thunderbird:*:*:*:*:-:*:*:* - VULNERABLE

Firefox < 149

Firefox ESR < 140.9

Thunderbird < 149

Thunderbird ESR < 140.9

PoC / Exploit Code

⚠ For Security Research Only

The following code is for security research and authorized testing only.

python

<!--
PoC for CVE-2026-4720 (Conceptual)
This PoC demonstrates a potential crash scenario.
Target: Firefox < 149, Thunderbird < 149
-->
<!DOCTYPE html>
<html>
<head>
    <title>CVE-2026-4720 PoC</title>
    <meta charset="UTF-8">
</head>
<body>
    <h1>Testing Memory Corruption</h1>
    <script>
        // Attempt to trigger the memory safety bug
        // Specific exploit pattern depends on the root cause (UAF, Buffer Overflow, etc.)
        // This is a placeholder for the actual trigger logic.
        try {
            var buffer = new ArrayBuffer(0x1000);
            var view = new DataView(buffer);
            // Manipulate memory to cause corruption
            for (var i = 0; i < 0x10000; i++) {
                view.setUint32(0, 0x41414141, true);
            }
            console.log("If crash occurs, vulnerability is confirmed.");
        } catch (e) {
            console.log("Error: " + e.message);
        }
    </script>
</body>
</html>

References

[1] CVE.org https://www.cve.org/CVERecord?id=CVE-2026-4720
[2] NVD NIST https://nvd.nist.gov/vuln/detail/CVE-2026-4720
[3] CVE Details https://www.cvedetails.com/cve/CVE-2026-4720/
[4] VulDB https://vuldb.com/cve/CVE-2026-4720
[5] https://bugzilla.mozilla.org/buglist.cgi?bug_id=2004652%2C2019372%2C2021922%2C2022567%2C2022733
[6] https://www.mozilla.org/security/advisories/mfsa2026-20/
[7] https://www.mozilla.org/security/advisories/mfsa2026-22/
[8] https://www.mozilla.org/security/advisories/mfsa2026-23/
[9] https://www.mozilla.org/security/advisories/mfsa2026-24/

Raw JSON Data

JSON

{"cve": {"id": "CVE-2026-4720", "sourceIdentifier": "[email protected]", "published": "2026-03-24T13:16:07.893", "lastModified": "2026-04-13T15:17:44.017", "vulnStatus": "Modified", "cveTags": [], "descriptions": [{"lang": "en", "value": "Memory safety bugs present in 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 140.9, Thunderbird 149, and Thunderbird 140.9."}, {"lang": "es", "value": "Errores de seguridad de memoria presentes en Firefox ESR 140.8, Thunderbird ESR 140.8, Firefox 148 y Thunderbird 148. Algunos de estos errores mostraron evidencia de corrupción de memoria y presumimos que con suficiente esfuerzo algunos de estos podrían haber sido explotados para ejecutar código arbitrario. Esta vulnerabilidad afecta a Firefox < 149, Firefox ESR < 140.9, Thunderbird < 149 y Thunderbird < 140.9."}], "metrics": {"cvssMetricV31": [{"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "type": "Secondary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H", "baseScore": 9.8, "baseSeverity": "CRITICAL", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "HIGH", "integrityImpact": "HIGH", "availabilityImpact": "HIGH"}, "exploitabilityScore": 3.9, "impactScore": 5.9}]}, "weaknesses": [{"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "type": "Secondary", "description": [{"lang": "en", "value": "CWE-120"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:a:mozilla:firefox:*:*:*:*:esr:*:*:*", "versionEndExcluding": "140.9.0", "matchCriteriaId": "DA62D95E-CB01-4586-83DB-5094116FC939"}, {"vulnerable": true, "criteria": "cpe:2.3:a:mozilla:firefox:*:*:*:*:-:*:*:*", "versionEndExcluding": "149.0", "matchCriteriaId": "02F2B82F-E997-4D5F-BBB0-237E4962555B"}, {"vulnerable": true, "criteria": "cpe:2.3:a:mozilla:thunderbird:*:*:*:*:esr:*:*:*", "versionEndExcluding": "140.9.0", "matchCriteriaId": "4C0558B1-4113-45A8-8E37-A0793A67AD6D"}, {"vulnerable": true, "criteria": "cpe:2.3:a:mozilla:thunderbird:*:*:*:*:-:*:*:*", "versionEndExcluding": "149.0", "matchCriteriaId": "40FE4697-89F1-46F6-8E28-41883647583B"}]}]}], "references": [{"url": "https://bugzilla.mozilla.org/buglist.cgi?bug_id=2004652%2C2019372%2C2021922%2C2022567%2C2022733", "source": "[email protected]", "tags": ["Broken Link"]}, {"url": "https://www.mozilla.org/security/advisories/mfsa2026-20/", "source": "[email protected]", "tags": ["Vendor Advisory"]}, {"url": "https://www.mozilla.org/security/advisories/mfsa2026-22/", "source": "[email protected]", "tags": ["Vendor Advisory"]}, {"url": "https://www.mozilla.org/security/advisories/mfsa2026-23/", "source": "[email protected]", "tags": ["Vendor Advisory"]}, {"url": "https://www.mozilla.org/security/advisories/mfsa2026-24/", "source": "[email protected]", "tags": ["Vendor Advisory"]}]}}