CVE-2025-62410: happy-dom's `--disallow-code-generation-from-strings` is not sufficient for isolating untrusted JavaScript

Should you act?

Critical, preconditions apply

Severe if exploited, but exploitation needs conditions that may not apply to you. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• Not in CISA KEV, but CISA’s SSVC assessment records a public proof-of-concept, so attack code exists.
• EPSS 0.4%, percentile 28: FIRST’s model estimates a 0.4% chance of exploitation activity in the next 30 days, higher than 28% of all scored CVEs (low). EPSS is a probability, not a verdict.
• Needs an account (low (any account)). Exposure depends on who can log in.
• Only applies if your dependency tree includes happy-dom (npm) >= 19.0.0, < 20.0.2, fixed in 20.0.2. Check your lockfile, including transitive dependencies.

What it is

In versions before 20.0.2, it was found that --disallow-code-generation-from-strings is not sufficient for isolating untrusted JavaScript in happy-dom. The untrusted script and the rest of the application still run in the same Isolate/process, so attackers can deploy prototype pollution payloads to hijack important references like "process" in the example below, or to hijack control flow via flipping checks of undefined property. This vulnerability is due to an incomplete fix for CVE-2025-61927. The vulnerability is fixed in 20.0.2.

From the GitHub advisory

Summary The mitigation proposed in GHSA-37j7-fg3j-429f for disabling eval/Function when executing untrusted code in happy-dom does not suffice, since it still allows prototype pollution payloads.

Details The untrusted script and the rest of the application still run in the same Isolate/process, so attackers can deploy prototype pollution payloads to hijack important references like "process" in the example below, or to hijack control flow via flipping checks of undefined property. There might be other payloads that allow the manipulation of require, e.g., via (univeral) gadgets (https://www.usenix.org/system/files/usenixsecurity23-shcherbakov.pdf).

PoC Attackers can pollute builtins like Object.prototype.hasOwnProperty() to obtain important references at runtime, e.g., "process". In this way, attackers might be able to execute arbitrary commands like in the example below via spawn().

Impact Arbitrary code execution via breaking out of the Node.js' vm isolation.

Recommended Immediate Actions Users can freeze the builtins in the global scope to defend against attacks similar to the PoC above. However, the untrusted code might still be able to retrieve all kind of information available in the global scope and exfiltrate them via fetch(), even without prototype pollution capabilities. Not to mention side channels caused by the shared process/isolate. Migration to isolated-vm is suggested instead.

Weakness type: CWE-1321.

Product: happy-dom (npm) · Assigned by: GitHub_M · Published: 2025-10-15

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Attack requirements: none
• Privileges required: low (any account)
• User interaction: passive

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
• CISA SSVC assessment: exploitation poc, automatable no, technical impact total.
• FIRST EPSS (model of 2026-10-21): 0.35% probability of exploitation activity in the next 30 days; percentile 28.

Timeline

• 2025-10-15 — CVE record last updated
• 2025-10-15 — CVE record published by GitHub_M
• 2025-10-15 — GitHub-reviewed advisory GHSA-qpm2-6cq5-7pq5 published (critical)

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vulnerability records

1. GitHub Advisory GHSA-qpm2-6cq5-7pq5 github.com
2. CVE.org record CVE-2025-62410 cve.org
3. NVD entry CVE-2025-62410 nvd.nist.gov

Other references from the CVE record and advisory

1. github.com github.com
2. github.com github.com

Critical npm advisories · Today’s Security Digest