Remote Code Execution in Happy DOM ECMAScriptModuleCompiler
CVE-2026-33943 is a code injection vulnerability in Happy DOM, affecting versions 15.10.0 through 20.8.7. The flaw resides in the ECMAScriptModuleCompiler, which processes ES module scripts. An attacker can inject arbitrary JavaScript expressions inside export { } declarations; the compiler directly interpolates this unsanitized content into generated code as an executable expression. The existing quote filter is insufficient because it does not strip backticks, allowing template literal-based payloads to bypass sanitization. Successful exploitation can result in remote code execution in the context where happy-dom processes the malicious module.
Are you exposed to this one?
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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.
Mitigation
If you can’t patch tonight, do this now.
export { } declarations. Restrict or sandbox execution contexts that run happy-dom so that arbitrary JavaScript execution has minimal access to the host environment and sensitive resources. Treat all module content as untrusted until the library is upgraded.Remediation
Patch, then assume compromise.
5437fdf8f13adb9590f9f52616d9f69c3ee8db3c and validate that all affected deployments are no longer using versions 15.10.0 through 20.8.7.Exploits
No public exploits tracked yet. Mallory keeps watching.
No public exploit code observed for this vulnerability.
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.
Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.
Recent activity
6 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
The version that knows your environment.
Query your assets running an affected version, and investigate the blast radius.
Every observed campaign linking this CVE to a named adversary.
Malware families riding this exploit, with evidence and IOCs.
YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.
Cross-references every affected SKU, including bundled OEM variants.
Community discussion across Reddit, Mastodon, and other social sources.