How severe is CVE-2021-3918?

CVE-2021-3918 has a CVSS score of 9.8/10, rated CRITICAL. Immediate patching is strongly recommended.

Which packages are affected by CVE-2021-3918?

Affected package information for CVE-2021-3918 is not yet fully mapped. Check the official advisory links for details.

How do I fix CVE-2021-3918?

No fixed version has been published for CVE-2021-3918 yet. Monitor the advisory for updates, apply mitigations recommended by the vendor, and use O3 Security to track when a fix becomes available in your stack.

Is CVE-2021-3918 actively exploited in the wild?

Yes. There are 1 known exploit references for CVE-2021-3918, including 1 in-the-wild exploitation observed on GitHub and other sources. Treat this as actively exploitable and prioritize patching immediately. All exploit code should only be run in an isolated sandbox environment for research or authorized testing — never against production systems without explicit written authorization.

What is the EPSS score for CVE-2021-3918?

CVE-2021-3918 has an EPSS (Exploit Prediction Scoring System) score of 1.3%, placing it in the 80th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

CVE-2021-3918

Q: Can O3 Security detect CVE-2021-3918 in my codebase?

Yes. O3 Security's Impact-Aware SCA scanner identifies CVE-2021-3918 across all affected ecosystems (multiple ecosystems), correlates it against your dependency graph, and uses function-level reachability to confirm whether the vulnerable code path is actually reachable in your application — eliminating false positives. You can scan your stack for CVE-2021-3918 directly from the O3 platform.

CRITICAL

Also known asGHSA-896r-f27r-55mw

Published

Nov 13, 2021

Updated

Apr 16, 2026

Affected

0 pkgs

Patched

None yet

Exploits

1 known

EPSS Exploitation Probability

via FIRST.org ↗

1.3%probability of exploitation in next 30 days

Lower Risk80th percentile0.00%

EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.

Description

json-schema is vulnerable to Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution')

Exploits & PoCs

Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.

json-schema is vulnerable to Improperly Controlled Modification of Objec…

huntr.devNVDNov 2021

Frequently Asked Questions

json-schema is vulnerable to Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution')

O3 Security · Impact-Aware SCA

Is CVE-2021-3918 in your stack?

O3 detects CVE-2021-3918 across dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.

Scan my stack How O3 SCA works

CVSS Score

9.8/10

CVSS v3 base score

Vector breakdown

AV:Attack Vector

Network

AC:Attack Complexity

Low

PR:Privileges Required

None

UI:User Interaction