CVE-2025-4086 | Specially crafted filename could be used to obscure download type

A specially crafted filename containing a large number of encoded newline characters could obscure the file's extension when displayed in the download dialog. *This bug only affects Thunderbird for Android. Other versions of Thunderbird are unaffected.*. This vulnerability was fixed in Firefox 138 and Thunderbird 138.

Published: 2025-04-29 Last update: 2026-04-13 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2025-4086 is rated Low Risk (31/100): CVSS Medium severity, with low exploitation likelihood (EPSS 0.24%). 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.

Exploit prediction scoring system (EPSS) score for CVE-2025-4086

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 2026-06-15 0.26% 0.24% -0.02%
2 2026-06-11 0.24% 0.26% +0.02%
3 2026-03-18 — 0.24% —

Full EPSS history (10 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2025-4086

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
6.5 3.1 MEDIUM
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:L)
Some sensitive info could get out, but not a total data dump.
Integrity (I:L)
Attackers could change some data, but it’s limited—not everything goes.
Availability (A:N)
Service keeps running; no real outage angle.
 3.9 2.5 134c704f-9b21-4f2e-91b3-4a467353bcc0

Weakness enumeration for CVE-2025-4086

OS Trackers for CVE-2025-4086

vendor priority summary link
alpine — CVE-2025-4086: 2 source package rows (firefox, thunderbird); 208 state rows across 2 repos (3.22-community, edge-community); fixed 0, open 208. https://security.alpinelinux.org/vuln/CVE-2025-4086
debian unimportant CVE-2025-4086 unimportant priority: Debian including 1 source packages (firefox), 1 status rows across 1 suites (sid): resolved 1. https://security-tracker.debian.org/tracker/CVE-2025-4086
redhat medium — https://access.redhat.com/security/cve/CVE-2025-4086
suse high — https://www.suse.com/security/cve/CVE-2025-4086/
ubuntu medium CVE-2025-4086 medium priority: Ubuntu including 2 source packages (firefox, thunderbird), 12 status rows across 6 suites (focal, jammy, noble, oracular, plucky, upstream): not-affected 9, DNE 2, needs-triage 1. https://ubuntu.com/security/CVE-2025-4086

Affected software / configurations for CVE-2025-4086

Vendor Product Version Raw CPE
mozilla firefox < 138.0 cpe:2.3:a:mozilla:firefox:*:*:*:*:-:*:*:*
mozilla thunderbird < 138.0 cpe:2.3:a:mozilla:thunderbird:*:*:*:*:-:*:*:*

References for CVE-2025-4086

cvelogic Threat Intelligence