CVE-2026-25047: deepHas vulnerable to Prototype Pollution via constructor.prototype

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.

• No confirmed exploitation. It is not in CISA’s KEV catalog and CISA’s SSVC assessment records no known exploitation. That can change quickly after a public write-up; re-check if you are affected.
• EPSS 0.8%, percentile 56: FIRST’s model estimates a 0.8% chance of exploitation activity in the next 30 days, higher than 56% of all scored CVEs (moderate). EPSS is a probability, not a verdict.
• Needs local access needed. Lower urgency for most teams unless an attacker could already run code on the machine.
• Only applies if your dependency tree includes deephas (npm) < 1.0.8, fixed in 1.0.8. Check your lockfile, including transitive dependencies.

What it is

deepHas provides a test for the existence of a nested object key and optionally returns that key. A prototype pollution vulnerability exists in version 1.0.7 of the deephas npm package that allows an attacker to modify global object behavior. This issue was fixed in version 1.0.8.

From the GitHub advisory

Summary A prototype pollution vulnerability exists in version 1.0.7 of the deephas npm package that allows an attacker to modify global object behavior. This issue was fixed in version 1.0.8.

Details The vulnerability resides in the add() function and indexer() function implemented within deepHas.js. Although version 1.0.7 attempts to prevent prototype pollution by checking property ownership (e.g., using Object.hasOwnProperty) and by checking against forbidden string usage (using String.prototype.indexOf), this check can be bypassed as shown in the PoC

By doing so, an attacker can inject properties into Object.prototype through a payload such as constructor.prototype.polluted or proto.polluted resulting in prototype pollution.

This issue affects all JavaScript runtimes that rely on npm packages (including Node.js, Deno, and Bun) and is independent of the operating system.

PoC Steps to reproduce 1. Install version 1.0.7 of deephas using npm install 2. Run one of the following code snippets:

Weakness type: CWE-1321.

Product: deephas (npm) · Assigned by: GitHub_M · Published: 2026-01-29

Affected and fixed versions

Severity scores

• Attack vector: local access needed
• Attack complexity: low
• Attack requirements: none
• Privileges required: none (no login)
• User interaction: none

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 none, automatable no, technical impact total.
• FIRST EPSS (model of 2026-10-21): 0.81% probability of exploitation activity in the next 30 days; percentile 56.

Timeline

• 2026-01-29 — CVE record published by GitHub_M
• 2026-01-29 — GitHub-reviewed advisory GHSA-2733-6c58-pf27 published (critical)
• 2026-02-02 — CVE record last updated

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-2733-6c58-pf27 github.com
2. CVE.org record CVE-2026-25047 cve.org
3. NVD entry CVE-2026-25047 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