What is CVE-2021-23543?

CVE-2021-23543 is a critical-severity vulnerability in Agoric Realms-Shim, classified under Improperly Controlled Modification of Object Prototype Attributes (Prototype Pollution). CVSS score: 9.8/10. Published 2022-01-10.

How severe is CVE-2021-23543?

Critical severity. CVSS v3 base score is 9.8 out of 10.

Prototype Pollution in Agoric Realms-Shim

CVE-2021-23543

All versions of package realms-shim are vulnerable to Sandbox Bypass via a Prototype Pollution attack vector.

Vulnerability class: Prototype Pollution

Published 2022-01-10 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 9.8 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

EPSS exploit prediction

EPSS: 0.018 (77.9th percentile), scored 2026-10-24.

Low probability of exploitation in the next 30 days, but still tracked. 78th percentile — 77.9% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.018 · newest: 0.018 · change: 0.000

Affected products

Agoric Realms-Shim
Realms-Shim — versions 0

Weakness classification (CWE)

CWE-1321 — Improperly Controlled Modification of Object Prototype Attributes (Prototype Pollution)

References

www.npmjs.com/package/realms-shim (Product, Third Party Advisory)
snyk.io/vuln/SNYK-JS-REALMSSHIM-2309908 (Exploit, Third Party Advisory)

Frequently asked questions

What is CVE-2021-23543?: CVE-2021-23543 is a critical-severity vulnerability in Agoric Realms-Shim, classified under Improperly Controlled Modification of Object Prototype Attributes (Prototype Pollution). CVSS score: 9.8/10. Published 2022-01-10.
How severe is CVE-2021-23543?: Critical severity. CVSS v3 base score is 9.8 out of 10.