Cyber Resilience

CVE-2025-5986

Mozilla Thunderbird ≤ 128.11.1

Published
11 June 2025
Modified
17 June 2026
Patch / advisory
View advisory
CVSS Score v3.1 6.5
Click a component to see what it means
Raw vectorCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
EPSS Score 0.0051 41th percentile
Risk Priority 51 floored blend · peak EPSS

Summary

CVE-2025-5986 is a medium-severity User Interface (UI) Misrepresentation of Critical Information (CWE-451) vulnerability in Mozilla Thunderbird. Its CVSS base score is 6.5 (Medium).

Operationally, exploitation aligns with the MITRE ATT&CK technique Phishing (T1566); ranked at the 41th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.

OWASP Top 10 for Web (2025)

A06:2025 Insecure Design

EU & UK References

Vulnerability Data

A crafted HTML email using mailbox:/// links can trigger automatic, unsolicited downloads of .pdf files to the user's desktop or home directory without prompting, even if auto-saving is disabled. This behavior can be abused to fill the disk with garbage…

more

data (e.g. using /dev/urandom on Linux) or to leak Windows credentials via SMB links when the email is viewed in HTML mode. While user interaction is required to download the .pdf file, visual obfuscation can conceal the download trigger. Viewing the email in HTML mode is enough to load external content. This vulnerability was fixed in Thunderbird 128.11.1 and Thunderbird 139.0.2.

CWE(s)
CWE-451

Related Threats

MITRE ATT&CK Enterprise Techniques

T1566 Phishing Initial Access
Adversaries may send phishing messages to gain access to victim systems.
attack.mitre.org →
T1566.002 Spearphishing Link Initial Access
Adversaries may send spearphishing emails with a malicious link in an attempt to gain access to victim systems.
attack.mitre.org →
T1566.003 Spearphishing via Service Initial Access
Adversaries may send spearphishing messages via third-party services in an attempt to gain access to victim systems.
attack.mitre.org →
T1598 Phishing for Information Reconnaissance
Adversaries may send phishing messages to elicit sensitive information that can be used during targeting.
attack.mitre.org →
T1598.003 Spearphishing Link Reconnaissance
Adversaries may send spearphishing messages with a malicious link to elicit sensitive information that can be used during targeting.
attack.mitre.org →
T1534 Internal Spearphishing Lateral Movement
After they already have access to accounts or systems within the environment, adversaries may use internal spearphishing to gain access to additional information or compromise other users within the same organization.
attack.mitre.org →
Derived from this CVE’s CWE(s) via the direct CWE→ATT&CK cross-walk.

CVEs Like This One

CVE-2026-3889Same product: Mozilla Thunderbird
CVE-2025-3523Same product: Mozilla Thunderbird
CVE-2025-8043Same product: Mozilla Thunderbird
CVE-2026-16403Same product: Mozilla Thunderbird
CVE-2026-8964Same product: Mozilla Thunderbird
CVE-2025-4086Same product: Mozilla Thunderbird
CVE-2024-6610Same product: Mozilla Thunderbird
CVE-2024-7529Same product: Mozilla Thunderbird
CVE-2025-3522Same product: Mozilla Thunderbird
CVE-2026-2919Same vendor: Mozilla

Affected Assets

mozilla
thunderbird
≤ 128.11.1 · 135.0 — 139.0.2

Mitigating Controls

Mitigating Controls (NIST CSF 2.0) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.

PR.PS-06 mostly match
prevents

Secure SDLC practices directly address design and implementation of accurate, non-spoofable UI elements.

PR.AT-01 partial match
prevents

User awareness training helps people recognize and avoid harm from UI misrepresentation such as phishing, but does not prevent the flaw itself.

Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.

A.8.29 Security testing in development and acceptance mostly match
finds

Security testing can detect UI misrepresentation vulnerabilities before deployment.

A.6.3 Information security awareness, education and training partial match
prevents

Security awareness training can teach users to recognize UI misrepresentation and phishing attempts.

A.8.23 Web filtering partial match
mitigates

Web filtering can block known phishing sites that exploit UI misrepresentation.

A.8.25 Secure development life cycle partial match
prevents

Secure development lifecycle includes UI/UX security requirements that can prevent misrepresentation of critical information.

A.8.26 Application security requirements partial match
prevents

Application security requirements can mandate proper display and validation of critical information in the UI.

A.8.28 Secure coding partial match
prevents

Secure coding practices can prevent UI flaws that obscure or spoof critical information.

References