CVE-2025-3522: Vulnerability in Mozilla Thunderbird
Thunderbird processes the X-Mozilla-External-Attachment-URL header to handle attachments which can be hosted externally. When an email is opened, Thunderbird accesses the specified URL to determine file size, and navigates to it when the user clicks the attachment. Because the URL is not validated or sanitized, it can reference internal resources like chrome:// or SMB share file:// links, potentially leading to hashed Windows credential leakage and opening the door to more serious security issues. This vulnerability was fixed in Thunderbird 137.0.2 and Thunderbird 128.9.2.
AI Analysis
Technical Summary
Mozilla Thunderbird versions prior to 137.0.2 and 128.9.2 process the X-Mozilla-External-Attachment-URL header to handle externally hosted attachments by accessing the specified URL to determine file size and navigating to it upon user interaction. Because the URL is not validated or sanitized, it can reference internal resources such as chrome:// or SMB share file:// links. This can lead to leakage of hashed Windows credentials and potentially enable more serious security issues. The vulnerability is tracked as CVE-2025-3522 with a CVSS 3.1 score of 6.3. Mozilla released official fixes in Thunderbird 137.0.2 and Thunderbird ESR 128.9.2. Related vulnerabilities include CVE-2025-2830 (information disclosure via /tmp directory listing) and CVE-2025-3523 (UI misrepresentation of attachment URLs), both also fixed in these versions.
Potential Impact
Successful exploitation of CVE-2025-3522 can lead to leakage of hashed Windows credentials due to Thunderbird accessing crafted attachment URLs referencing internal resources. This credential leakage could facilitate further attacks. The vulnerability has medium severity with impact on confidentiality, integrity, and availability (all rated low to medium). Related vulnerabilities can disclose sensitive system information or mislead users into downloading content from untrusted sources. No known exploits in the wild have been reported at this time.
Mitigation Recommendations
This vulnerability is fixed in Mozilla Thunderbird versions 137.0.2 and ESR 128.9.2. Users and administrators should update to these versions or later to remediate the issue. Since official fixes are available, applying these updates is the recommended and effective mitigation. No additional action is required beyond updating Thunderbird to the fixed versions.
CVE-2025-3522: Vulnerability in Mozilla Thunderbird
Description
Thunderbird processes the X-Mozilla-External-Attachment-URL header to handle attachments which can be hosted externally. When an email is opened, Thunderbird accesses the specified URL to determine file size, and navigates to it when the user clicks the attachment. Because the URL is not validated or sanitized, it can reference internal resources like chrome:// or SMB share file:// links, potentially leading to hashed Windows credential leakage and opening the door to more serious security issues. This vulnerability was fixed in Thunderbird 137.0.2 and Thunderbird 128.9.2.
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
Mozilla Thunderbird versions prior to 137.0.2 and 128.9.2 process the X-Mozilla-External-Attachment-URL header to handle externally hosted attachments by accessing the specified URL to determine file size and navigating to it upon user interaction. Because the URL is not validated or sanitized, it can reference internal resources such as chrome:// or SMB share file:// links. This can lead to leakage of hashed Windows credentials and potentially enable more serious security issues. The vulnerability is tracked as CVE-2025-3522 with a CVSS 3.1 score of 6.3. Mozilla released official fixes in Thunderbird 137.0.2 and Thunderbird ESR 128.9.2. Related vulnerabilities include CVE-2025-2830 (information disclosure via /tmp directory listing) and CVE-2025-3523 (UI misrepresentation of attachment URLs), both also fixed in these versions.
Potential Impact
Successful exploitation of CVE-2025-3522 can lead to leakage of hashed Windows credentials due to Thunderbird accessing crafted attachment URLs referencing internal resources. This credential leakage could facilitate further attacks. The vulnerability has medium severity with impact on confidentiality, integrity, and availability (all rated low to medium). Related vulnerabilities can disclose sensitive system information or mislead users into downloading content from untrusted sources. No known exploits in the wild have been reported at this time.
Mitigation Recommendations
This vulnerability is fixed in Mozilla Thunderbird versions 137.0.2 and ESR 128.9.2. Users and administrators should update to these versions or later to remediate the issue. Since official fixes are available, applying these updates is the recommended and effective mitigation. No additional action is required beyond updating Thunderbird to the fixed versions.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- mozilla
- Date Reserved
- 2025-04-11T15:23:30.875Z
- Cvss Version
- 3.1
- State
- PUBLISHED
- Remediation Level
- null
- Vendor Advisory Urls
- [{"url":"https://www.mozilla.org/security/advisories/mfsa2025-26/","vendor":"Mozilla"},{"url":"https://www.mozilla.org/security/advisories/mfsa2025-27/","vendor":"Mozilla"}]
Threat ID: 69dd057b82d89c981f0174e6
Added to database: 4/13/2026, 3:02:19 PM
Last enriched: 4/13/2026, 3:18:01 PM
Last updated: 4/13/2026, 5:34:17 PM
Views: 4
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