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Sandbox escape in Firefox DOM Workers

IdentifiersCVE-2026-12294CWE-693

CVE-2026-12294 is a sandbox escape vulnerability in the DOM: Workers component of Mozilla Firefox and related Mozilla products. The available advisory text identifies the issue only at a high level as a 'Sandbox escape in the DOM: Workers component' and does not provide vulnerable function names, root-cause details, or exploitation mechanics. The flaw affects older releases prior to Firefox 152, Firefox ESR 140.12, Firefox ESR 115.37, Thunderbird 152, and Thunderbird 140.12. The issue is notable because Mozilla grouped it with other sandbox escape weaknesses and indicated that specially crafted web content could be used as part of exploitation chains.

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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 allows an attacker to escape the browser sandbox from the DOM Workers context. On its own, this weakens or defeats a key browser isolation boundary. In practical attack chains, this can enable code or actions that were previously confined to a sandboxed browser process to interact with the underlying system or higher-privilege browser components. The provided content specifically notes that sandbox escape flaws such as CVE-2026-12294 may be chained with memory corruption vulnerabilities, for example CVE-2026-12291, to achieve full browser-to-system compromise.

Mitigation

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

No vendor-provided workaround is described in the supplied content. Until patching is completed, reduce exposure by limiting access to untrusted web content, enforcing least privilege for end users, avoiding administrative execution contexts, enabling available exploit-protection controls, using application allowlisting and host-based detection/prevention, and restricting unauthorized scripts, libraries, and risky downloads. These measures only reduce risk and do not replace upgrading to fixed versions.

Remediation

Patch, then assume compromise.

Upgrade to a fixed Mozilla release. The vulnerability is fixed in Firefox 152, Firefox ESR 140.12, Firefox ESR 115.37, Thunderbird 152, and Thunderbird 140.12. Debian users should apply the corresponding firefox-esr package update referenced in DSA-6350-1. Standard remediation is prompt patch deployment across affected desktop and enterprise-managed installations.
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

Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.

ACTIVITY FEED

Recent activity

7 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.

7 SOURCESView more in app
What this page doesn’t show

The version that knows your environment.

This page is what’s public. Mallory adds the parts that aren’t: which of your assets are affected, which adversaries are exploiting it right now, which detections to deploy, and what to do tonight.
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Exposure mapping

Query your assets running an affected version, and investigate the blast radius.

Threat actor evidence

Every observed campaign linking this CVE to a named adversary.

Associated malware

Malware families riding this exploit, with evidence and IOCs.

Detection signatures

YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.

Vendor-by-vendor mapping

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

Social activity

Community discussion across Reddit, Mastodon, and other social sources.

EXTERNAL REFERENCES
MITRE CVE
cve.org · CVE-2026-12294
NVD
nvd.nist.gov/vuln/detail/CVE-2026-12294
MITRE CWE · CWE-693
cwe.mitre.org
bugzilla.mozilla.org
bugzilla.mozilla.org/show_bug.cgi?id=2039873
mozilla.org
mozilla.org/security/advisories/mfsa2026-57
mozilla.org
mozilla.org/security/advisories/mfsa2026-58
mozilla.org
mozilla.org/security/advisories/mfsa2026-59
mozilla.org
mozilla.org/security/advisories/mfsa2026-60
mozilla.org
mozilla.org/security/advisories/mfsa2026-61