CVE-2025-3877

Severity Score

5.4

*CVSS v3.1

Exploit Likelihood

*EPSS

Affected Versions

*CPE

Public Exploits

*Multiple Sources

Exploited in Wild

*KEV

Decision

Track

*SSVC

Descriptions

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 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 affects Thunderbird < 128.10.1 and Thunderbird < 138.0.1.

*Credits: Dario Weißer

CVSS Scores

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

Required

Scope

Unchanged

Confidentiality

Low

Integrity

None

Availability

Low

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

Required

Scope

Unchanged

Confidentiality

High

Integrity

None

Availability

None

Attack Vector

Network

Attack Complexity

Medium

Authentication

None

Confidentiality

Partial

Integrity

None

Availability

None

* Common Vulnerability Scoring System

SSVC

Decision:Track

Exploitation

None

Automatable

Tech. Impact

Partial

* Organization's Worst-case Scenario

Timeline

2025-04-22 CVE Reserved
2025-05-14 CVE Published
2025-05-15 CVE Updated
2025-05-16 EPSS Updated
---------- Exploited in Wild
---------- KEV Due Date
---------- First Exploit

CWE

CWE-200: Exposure of Sensitive Information to an Unauthorized Actor

CAPEC

References (3)

URL	Tag	Source
https://bugzilla.mozilla.org/show_bug.cgi?id=1958580
https://www.mozilla.org/security/advisories/mfsa2025-34
https://www.mozilla.org/security/advisories/mfsa2025-35

URL	Date	SRC

URL	Date	SRC

URL	Date	SRC

Affected Vendors, Products, and Versions

Vendor		Product				Version		Other		Status
Vendor	Product	Version	Other	Status	<-- -->	Vendor	Product	Version	Other	Status
Mozilla Search vendor "Mozilla"		Thunderbird Search vendor "Mozilla" for product "Thunderbird"				*		-		Affected