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.
Conclusion & alert: CVE-2025-3522 is rated Low Risk (34.6/100): CVSS Medium severity, with low exploitation likelihood (EPSS 0.10%). Mandatory action: Monitor for updates and reassess as exploit intelligence or EPSS changes.
Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.
EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).
| # | Date | Old EPSS score | New EPSS score | Delta (New - Old) |
|---|---|---|---|---|
| 1 | 2026-05-24 | 0.23% | 0.10% | -0.13% |
| 2 | 2026-02-09 | 0.06% | 0.23% | +0.17% |
| 3 | 2025-12-21 | — | 0.06% | — |
Full EPSS history (10 records total)
CVSS metrics for this CVE.
| Base score | Version | Severity | Vector | Exploitability | Impact | Score source |
|---|---|---|---|---|---|---|
| 6.3 | 3.1 | MEDIUM |
|
2.8 | 3.4 | 134c704f-9b21-4f2e-91b3-4a467353bcc0 |
| vendor | priority | summary | link |
|---|---|---|---|
alpine
|
— | CVE-2025-3522: 1 source package rows (thunderbird); 68 state rows across 2 repos (3.22-community, edge-community); fixed 0, open 68. | https://security.alpinelinux.org/vuln/CVE-2025-3522 |
debian
|
not yet assigned | CVE-2025-3522 not yet assigned priority: Debian including 1 source packages (thunderbird), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5. | https://security-tracker.debian.org/tracker/CVE-2025-3522 |
redhat
|
high | — | https://access.redhat.com/security/cve/CVE-2025-3522 |
suse
|
high | CVE-2025-3522 severity important: SUSE including 15 source package names (MozillaFirefox, MozillaFirefox-branding-upstream, …), 90 product×package rows across 27 product lines (SLES-LTSS-TERADATA 15 SP2, SUSE Liberty Linux 8, … (27 product lines)): Known Not Affected 75, Fixed 15. | https://www.suse.com/security/cve/CVE-2025-3522/ |
ubuntu
|
medium | CVE-2025-3522 medium priority: Ubuntu including 1 source packages (thunderbird), 6 status rows across 6 suites (focal, jammy, noble, oracular, plucky, upstream): not-affected 3, released 2, DNE 1. | https://ubuntu.com/security/CVE-2025-3522 |
| Vendor | Product | Version | Raw CPE |
|---|---|---|---|
| mozilla | thunderbird | < 128.9.2 | cpe:2.3:a:mozilla:thunderbird:*:*:*:*:*:*:*:* |
| mozilla | thunderbird | >= 129.0, < 137.0.2 | cpe:2.3:a:mozilla:thunderbird:*:*:*:*:*:*:*:* |
| URL | Tags |
|---|---|
| https://bugzilla.mozilla.org/show_bug.cgi?id=1955372 | Permissions Required |
| https://www.mozilla.org/security/advisories/mfsa2025-26/ | Vendor Advisory |
| https://www.mozilla.org/security/advisories/mfsa2025-27/ | Vendor Advisory |