What is CVE-2021-20487?

CVE-2021-20487 is a critical-severity vulnerability in IBM 8335-Gth, classified under Improper Verification of Cryptographic Signature. CVSS score: 9.1/10. Published 2021-05-26.

How severe is CVE-2021-20487?

Critical severity. CVSS v3 base score is 9.1 out of 10.

Vulnerability in IBM 8335-Gth

CVE-2021-20487

IBM Power9 Self Boot Engine(SBE) could allow a privileged user to inject malicious code and compromise the integrity of the host firmware bypassing the host firmware signature verification process.

Published 2021-05-26 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 9.1 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:H.

EPSS exploit prediction

EPSS: 0.007 (51.9th percentile), scored 2026-10-25.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 52nd percentile — 51.9% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.007 · newest: 0.007 · change: 0.000

Affected products

Weakness classification (CWE)

CWE-347 — Improper Verification of Cryptographic Signature

References

www.ibm.com/support/pages/node/6455911 (Vendor Advisory)
exchange.xforce.ibmcloud.com/vulnerabilities/197730 (VDB Entry, vdb-entry, Vendor Advisory)

Frequently asked questions

What is CVE-2021-20487?: CVE-2021-20487 is a critical-severity vulnerability in IBM 8335-Gth, classified under Improper Verification of Cryptographic Signature. CVSS score: 9.1/10. Published 2021-05-26.
How severe is CVE-2021-20487?: Critical severity. CVSS v3 base score is 9.1 out of 10.