CVE-2021-27562: Arm Trusted Firmware Out-of-Bounds Write Vulnerability

Is it exploited?

Yes. CISA added it to the Known Exploited Vulnerabilities catalog on 3 Nov 2021, 162 days after the CVE record was published.

How likely is exploitation in the next 30 days?

3.1%

EPSS score, percentile 87.6 of all scored records

How severe?

5.5 Medium

CVSS v3.1 base score, from CISA's enrichment of the record

What should I do?

CISA deadline 17 Nov 2021. Apply updates per vendor instructions.

The CVE record links no vendor advisory, patch or mitigation.

Which versions are affected?

Not stated. The CVE record gives vendor and product as “n/a” and the version as “unspecified”.

Source: CISA Known Exploited Vulnerabilities (KEV) catalog, 2026.10.28, as of 28 Oct 2026; FIRST Exploit Prediction Scoring System (EPSS), v2026.06.15, as of 28 Oct 2026; CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of 28 Oct 2026. About the data.

What to do

CISA due date for this action: 17 November 2021.

Advisories and patches

The CVE record links no vendor advisory, patch or mitigation.

Linked from CISA's catalog entry

• https://nvd.nist.gov/vuln/detail/CVE-2021-27562

Affected products and versions

The CVE record does not name affected products or versions: vendor and product are “n/a” and the version is “unspecified”.

Source: CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of 28 Oct 2026. About the data.

About this vulnerability

Arm Trusted Firmware contains an out-of-bounds write vulnerability allowing the non-secure (NS) world to trigger a system halt, overwrite secure data, or print out secure data when calling secure functions under the non-secure processing environment (NSPE) handler mode. This vulnerability affects Yealink Device Management servers.

Summary: CISA's KEV catalog, as of 28 Oct 2026.

• CISA added CVE-2021-27562 to its Known Exploited Vulnerabilities (KEV) catalog on 3 Nov 2021.
• CISA's ransomware flag for this entry is "Unknown": no evidence of ransomware use in the catalog, which is not proof of none.
• The due date CISA sets for the required action is 17 Nov 2021.
• The CVE record was published on 25 May 2021, 162 days before it was added to KEV.
• The CVE record carries a CVSS v3.1 base score of 5.5 (Medium), taken from CISA's enrichment of the record.
• FIRST's EPSS model puts the probability of exploitation in the next 30 days at 3.1% (percentile 87.6), as of 28 Oct 2026.
• CISA's SSVC assessment in the CVE record: exploitation active, automatable no, technical impact partial.

Source: CISA Known Exploited Vulnerabilities (KEV) catalog, 2026.10.28, as of 28 Oct 2026; CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of 28 Oct 2026; FIRST Exploit Prediction Scoring System (EPSS), v2026.06.15, as of 28 Oct 2026. About the data.

Description

In Arm Trusted Firmware M through 1.2, the NS world may trigger a system halt, an overwrite of secure data, or the printing out of secure data when calling secure functions under the NSPE handler mode.

Source: CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of 28 Oct 2026. About the data.

Weakness

• CWE-787: Out-of-bounds Write

CWE and CAPEC are maintained by MITRE; the entries are those named in the CVE record and the KEV entry.

Timeline

References

• developer.arm.com
• git.trustedfirmware.org

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