CVE-2025-4083 [Critical] | Security Bypass in Firefox

A process isolation vulnerability in Thunderbird stemmed from improper handling of javascript: URIs, which could allow content to execute in the top-level document's process instead of the intended frame, potentially enabling a sandbox escape. This vulnerability was fixed in Firefox 138, Firefox ESR 128.10, Firefox ESR 115.23, Thunderbird 138, and Thunderbird 128.10.

#	Date	Old EPSS score	New EPSS score	Delta (New - Old)
1	2026-06-15	0.22%	0.36%	+0.14%
2	2026-06-07	0.34%	0.22%	-0.11%
3	2026-05-25	—	0.34%	—

Date

Old EPSS score

New EPSS score

Delta (New - Old)

2026-06-15

0.22%

0.36%

+0.14%

2026-06-07

0.34%

0.22%

-0.11%

2026-05-25

—

0.34%

—

Base score	Version	Severity	Vector	Exploitability	Impact	Score source
9.1	3.1	CRITICAL	`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/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:H) Serious risk that confidential data gets exposed in a big way. Integrity (I:H) They could widely tamper with or forge data—trust in the data is badly hurt. Availability (A:N) Service keeps running; no real outage angle.	3.9	5.2	134c704f-9b21-4f2e-91b3-4a467353bcc0

Base score

Version

Severity

Vector

Exploitability

Impact

Score source

9.1

3.1

CRITICAL

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/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:H): Serious risk that confidential data gets exposed in a big way.
Integrity (I:H): They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:N): Service keeps running; no real outage angle.

3.9

5.2

134c704f-9b21-4f2e-91b3-4a467353bcc0

OS Trackers for CVE-2025-4083

vendor	priority	summary	link
`alpine`	—	CVE-2025-4083: 3 source package rows (firefox, firefox-esr, thunderbird); 353 state rows across 2 repos (3.22-community, edge-community); fixed 0, open 353.	https://security.alpinelinux.org/vuln/CVE-2025-4083
`debian`	not yet assigned	CVE-2025-4083 not yet assigned priority: Debian including 3 source packages (firefox, firefox-esr, thunderbird), 11 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 11.	https://security-tracker.debian.org/tracker/CVE-2025-4083
`redhat`	high	—	https://access.redhat.com/security/cve/CVE-2025-4083
`suse`	high	CVE-2025-4083 severity important: SUSE including 23 source package names (MozillaFirefox-128.10.0-150200.152.179.1, MozillaFirefox-138.0-1.1, …), 105 product×package rows across 38 product lines (Container suse/kiosk/firefox-esr, Image SLES15-SP3-SAP-Azure-LI-BYOS-Production, … (38 product lines)): Fixed 105.	https://www.suse.com/security/cve/CVE-2025-4083/
`ubuntu`	medium	CVE-2025-4083 medium priority: Ubuntu including 9 source packages (firefox, mozjs102, …), 65 status rows across 8 suites (bionic, focal, jammy, noble, oracular, plucky, questing, upstream): DNE 35, ignored 10, not-affected 9, needs-triage 8, released 3.	https://ubuntu.com/security/CVE-2025-4083

Affected software / configurations for CVE-2025-4083

Vendor	Product	Version	Raw CPE
mozilla	firefox	< 115.23	cpe:2.3:a:mozilla:firefox:::::esr:::*
mozilla	firefox	< 138.0	cpe:2.3:a:mozilla:firefox:::::-:::*
mozilla	firefox	>= 128.0, < 128.10	cpe:2.3:a:mozilla:firefox:::::esr:::*
mozilla	thunderbird	< 128.10.0	cpe:2.3:a:mozilla:thunderbird:::::esr:::*
mozilla	thunderbird	< 138.0	cpe:2.3:a:mozilla:thunderbird:::::-:::*

References for CVE-2025-4083

URL	Tags
https://bugzilla.mozilla.org/show_bug.cgi?id=1958350	Permissions Required
https://www.mozilla.org/security/advisories/mfsa2025-28/	Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2025-29/	Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2025-30/	Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2025-31/	Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2025-32/	Vendor Advisory
https://lists.debian.org/debian-lts-announce/2025/05/msg00024.html

URL

CVE-2025-4083 | Process isolation bypass using "javascript:" URI links in cross-origin frames

Exploit prediction scoring system (EPSS) score for CVE-2025-4083

Common vulnerability scoring system (CVSS) metrics for CVE-2025-4083

Weakness enumeration for CVE-2025-4083

OS Trackers for CVE-2025-4083

Affected software / configurations for CVE-2025-4083

References for CVE-2025-4083