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Sandbox escape in Firefox DOM: Workers component

IdentifiersCVE-2026-12294CWE-693

CVE-2026-12294 is a sandbox escape vulnerability in the DOM: Workers component of Mozilla Firefox and Thunderbird. The available advisory content identifies the issue only at a high level as a sandbox escape affecting the Workers subsystem; no vulnerable function, root cause, or triggering code path is provided in the supplied material. Mozilla states the issue was fixed in Firefox 152, Firefox ESR 140.12, Firefox ESR 115.37, Thunderbird 152, and Thunderbird 140.12.

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ANALYST BRIEF

Impact, mitigation & remediation

What it means. What to do now. Patch path, mitigations, and the assume-compromise checklist.

Impact

What an attacker gets, and what they’ve been doing with it.

Successful exploitation could allow an attacker to escape the browser sandbox from the affected DOM: Workers context. In practical terms, this can weaken or bypass a key browser isolation boundary and may enable follow-on actions with greater access to the host or browser process than intended. The supplied advisories discuss sandbox escape as part of broader Mozilla vulnerability sets, but do not provide CVE-specific detail beyond the sandbox escape outcome.

Mitigation

If you can’t patch tonight, do this now.

No CVE-specific workaround or temporary mitigation is provided in the supplied advisories. The primary mitigation is prompt patching to the fixed Mozilla or downstream vendor versions. General hardening measures noted in broader advisories include enforcing least privilege, avoiding administrative user contexts, enabling exploit protections, and limiting exposure to untrusted web content until updates are applied.

Remediation

Patch, then assume compromise.

Upgrade affected products to a fixed release. The supplied content states that CVE-2026-12294 is fixed in Firefox 152, Firefox ESR 140.12, Firefox ESR 115.37, Thunderbird 152, and Thunderbird 140.12. Debian users should upgrade firefox-esr to the vendor-provided fixed package version referenced in DSA-6350-1.
PUBLIC EXPLOITS

Exploits

No public exploits tracked yet. Mallory keeps watching.

VALID 0 / 0 TOTALView more in app

No public exploit code observed for this vulnerability.

EXPOSURE SURFACE

Affected products & vendors

Products and vendors Mallory has correlated with this vulnerability. Open in Mallory to drill down to specific CPE configurations and version ranges.

VendorProductType
MozillaFirefoxapplication
MozillaFirefox Esrapplication

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What this page doesn’t show

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Exposure mapping

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Threat actor evidence

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Associated malware

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Detection signatures

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Vendor-by-vendor mapping

Cross-references every affected SKU, including bundled OEM variants.

Social activity

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