CVE-2026-12294 | Sandbox escape in the DOM: Workers component

Sandbox escape in the DOM: Workers component. This vulnerability was fixed in Firefox 152, Firefox ESR 140.12, Firefox ESR 115.37, Thunderbird 152, and Thunderbird 140.12.

Published: 2026-06-16 Last update: 2026-06-30 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2026-12294 is rated Moderate Risk (48.3/100): CVSS Critical severity, with low exploitation likelihood (EPSS 0.36%). Review affected assets and schedule remediation.

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-2026-12294

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 2026-06-30 0.31% 0.36% +0.05%
2 2026-06-19 0.16% 0.31% +0.16%
3 2026-06-17 — 0.16% —

Full EPSS history (3 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2026-12294

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
9.6 3.1 CRITICAL
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H 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:R)
A real person has to do something—click, install, enable—otherwise it doesn’t land.
Scope (S:C)
Breaking this can reach past the original component and bite other resources—bigger blast radius.
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:H)
Could take the service down hard or make it unusable for people who depend on it.
 2.8 6.0 134c704f-9b21-4f2e-91b3-4a467353bcc0
7.5 3.1 HIGH
CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H 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:H)
Even with access, the exploit needs extra luck, timing, or a fussy environment to actually work.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:R)
A real person has to do something—click, install, enable—otherwise it doesn’t land.
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:H)
Could take the service down hard or make it unusable for people who depend on it.
 1.6 5.9 0b0ca135-0b70-47e7-9f44-1890c2a1c46c

Weakness enumeration for CVE-2026-12294

GitHub Security Advisory for CVE-2026-12294

GHSA-j3ch-r4qx-fpvf · Severity: critical — Sandbox escape in the DOM: Workers component. This vulnerability was fixed in Firefox 152,...

OS Trackers for CVE-2026-12294

vendor priority summary link
debian not yet assigned CVE-2026-12294 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-2026-12294
suse critical — https://www.suse.com/security/cve/CVE-2026-12294/
ubuntu medium CVE-2026-12294 medium priority: Ubuntu including 9 source packages (firefox, mozjs102, …), 49 status rows across 7 suites (bionic, focal, jammy, noble, questing, resolute, upstream): DNE 23, needs-triage 10, ignored 8, not-affected 7, needed 1. https://ubuntu.com/security/CVE-2026-12294

Affected software / configurations for CVE-2026-12294

Vendor Product Version Raw CPE
mozilla firefox < 115.37.0 cpe:2.3:a:mozilla:firefox:*:*:*:*:esr:*:*:*
mozilla firefox < 152.0.0 cpe:2.3:a:mozilla:firefox:*:*:*:*:-:*:*:*
mozilla firefox >= 128.0, < 140.12.0 cpe:2.3:a:mozilla:firefox:*:*:*:*:esr:*:*:*
mozilla thunderbird < 140.12.0 cpe:2.3:a:mozilla:thunderbird:*:*:*:*:esr:*:*:*
mozilla thunderbird < 152.0.0 cpe:2.3:a:mozilla:thunderbird:*:*:*:*:-:*:*:*

References for CVE-2026-12294

URL Tags
https://bugzilla.mozilla.org/show_bug.cgi?id=2039873 Permissions Required
https://www.mozilla.org/security/advisories/mfsa2026-57/ Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2026-58/ Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2026-59/ Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2026-60/ Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2026-61/ Vendor Advisory
https://access.redhat.com/errata/RHSA-2026:27717
https://access.redhat.com/errata/RHSA-2026:27733
https://access.redhat.com/errata/RHSA-2026:27734
https://access.redhat.com/errata/RHSA-2026:29940
https://access.redhat.com/errata/RHSA-2026:30846
https://access.redhat.com/errata/RHSA-2026:33445
https://access.redhat.com/security/cve/CVE-2026-12294
https://bugzilla.redhat.com/show_bug.cgi?id=2489207
https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-12294.json
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