CVE-2021-3918 | Prototype Pollution in kriszyp/json-schema

Exp

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

Published: 2021-11-13 Last update: 2026-06-17 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2021-3918 is rated High Exploit Risk (87.2/100): CVSS Critical severity, with medium exploitation likelihood (EPSS 3.56%). 1 public exploit reference(s) are indexed (Exploit-DB). EPSS rose +2.30% over the last day, indicating growing attacker interest. Public exploits are available—assess exposure, apply mitigations, and prioritize patching.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Public exploit references (Exploit-DB) for CVE-2021-3918

EDB-ID Source Kind Published Link
— nvd_ref exploit_tag Exploit-DB ↗

Exploit prediction scoring system (EPSS) score for CVE-2021-3918

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-15 1.26% 3.56% +2.30%
2 2026-03-25 1.16% 1.26% +0.10%
3 2026-03-04 — 1.16% —

Full EPSS history (58 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-3918

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
9.8 3.1 CRITICAL
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 3.9 5.9 [email protected]
9.8 3.0 CRITICAL
CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 3.9 5.9 [email protected]
7.5 2.0 HIGH
AV:N/AC:L/Au:N/C:P/I:P/A:P Click to expand
Access vector (AV:N)
Can be exploited remotely over network reachability.
Access complexity (AC:L)
Exploitation conditions are straightforward and predictable.
Authentication (AU:N)
No authentication is required.
Confidentiality impact (C:P)
Partial confidentiality impact.
Integrity impact (I:P)
Partial integrity impact.
Availability impact (A:P)
Partial availability impact.
 10.0 6.4 [email protected]

Weakness enumeration for CVE-2021-3918

GitHub Security Advisory for CVE-2021-3918

GHSA-896r-f27r-55mw · Severity: critical · Ecosystem: npm — json-schema is vulnerable to Prototype Pollution

OS Trackers for CVE-2021-3918

vendor priority summary link
debian not yet assigned CVE-2021-3918 not yet assigned priority: Debian including 1 source packages (node-json-schema), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5. https://security-tracker.debian.org/tracker/CVE-2021-3918
redhat high — https://access.redhat.com/security/cve/CVE-2021-3918
suse high CVE-2021-3918 severity important: SUSE including 173 source package names (12-11.15:nodejs12-12.22.10-4.29.3, 12-11.15:npm12-12.22.10-4.29.3, …), 659 product×package rows across 51 product lines (Container bci/nodejs, Container ses/7.1/ceph/grafana, … (51 product lines)): Fixed 649, Known Not Affected 10. https://www.suse.com/security/cve/CVE-2021-3918/
ubuntu medium CVE-2021-3918 medium priority: Ubuntu including 1 source packages (node-json-schema), 10 status rows across 10 suites (bionic, focal, hirsute, impish, jammy, kinetic, lunar, trusty, upstream, xenial): ignored 4, not-affected 3, released 3. https://ubuntu.com/security/CVE-2021-3918

Affected software / configurations for CVE-2021-3918

Vendor Product Version Raw CPE
json-schema_project json-schema < 0.4.0 cpe:2.3:a:json-schema_project:json-schema:*:*:*:*:*:*:*:*
debian debian_linux 10.0 cpe:2.3:o:debian:debian_linux:10.0:*:*:*:*:*:*:*

References for CVE-2021-3918

cvelogic Threat Intelligence