CVE-2021-27562
CVE-2021-27562 is a security flaw in Arm Trusted Firmware. Attackers can corrupt memory in Arm Trusted Firmware, which they use to take it over. The US Cybersecurity and Infrastructure Security Agency (CISA) added it to its catalog of flaws known to be used in attacks on 3 Nov 2021.[1]
Arm Trusted Firmware is in things households have, such as phones, computers, browsers and everyday apps, so the fix matters at home as much as at work. Arm has published a fix or advice.
Description
CISA calls it an out-of-bounds write in Arm Trusted Firmware. In its words: “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.”[1]
The underlying weakness is out-of-bounds write (CWE-787), in MITRE’s list of common software weaknesses.[2]
It scores 5.5 out of 10 on the Common Vulnerability Scoring System, which rates it medium, scored by NVD using CVSS 3.1.[2]
Affected versions
NVD’s record doesn’t list version ranges for it; Arm’s advisory has them[3]. CISA names the product as Arm Trusted Firmware.
Every device with Arm Trusted Firmware needs the update.
Exploitation
CISA added it to its catalog of known exploited vulnerabilities on 3 Nov 2021, 162 days after it was made public. CISA lists a flaw only when it has reliable evidence of it being exploited, and gave US federal agencies until 17 Nov 2021 to fix it.[1]
FIRST’s Exploit Prediction Scoring System, which estimates how likely a flaw is to be used in attacks in the next 30 days from what it sees across the internet, puts it at 3%. That’s in the top 13% of the flaws it scores.[4]
CISA assesses it as not automatable: each attack takes some work.
CISA doesn’t say who was attacked, or how.
Fix
Arm has published a fix or advice.[3] CISA’s required action: “Apply updates per vendor instructions.”[1]
- Update Arm Trusted Firmware now.Install the latest update from Arm on every device that has it, and restart when asked. Then turn on automatic updates, so the next fix arrives on its own.
- If there’s no update, stop using it.CISA’s advice when a flaw being used in attacks has no fix is to stop using the product until it does.
Timeline
| Date | Event |
|---|---|
| The flaw is made public in the National Vulnerability Database, with a severity score of 5.5.[2] | |
| CISA adds it to its catalog of flaws known to be used in attacks.[1] | |
| CISA’s deadline for US government agencies to fix it.[1] | |
| FIRST puts the odds of it being used in attacks in the next 30 days at 3%.[4] |
See also
Other Arm flaws
- CVE-2024-4610, Arm Mali GPU Kernel Driver: use-after-free ·
- CVE-2023-4211, Arm Mali GPU Kernel Driver: use-after-free ·
- CVE-2021-29256, Arm Mali Graphics Processing Unit (GPU): mali GPU kernel driver use-after-free ·
- CVE-2023-26083, Arm Mali Graphics Processing Unit (GPU): mali GPU kernel driver information disclosure ·
- CVE-2022-38181, Arm Mali Graphics Processing Unit (GPU): mali GPU kernel driver use-after-free ·
Other out-of-bounds write flaws
- CVE-2026-86950, Apple devices: out-of-bounds write ·
- CVE-2026-53266, Linux Kernel: out-of-bounds write ·
- CVE-2026-87491, Chrome and other Chromium browsers: out of bounds write ·
- CVE-2026-53362, Linux Kernel: unspecified ·
- CVE-2022-0995, Linux Kernel: out-of-bounds write ·
Added the same day
- CVE-2021-42258, BQE BillQuick Web Suite: SQL injection ·
- CVE-2021-42013, Apache HTTP Server: path traversal ·
- CVE-2021-41773, Apache HTTP Server: path traversal ·
- CVE-2021-40539, Zoho ManageEngine: aDSelfService plus authentication bypass ·
- CVE-2021-40444, Microsoft MSHTML: remote code execution ·
Every Arm flaw on CISA’s list · Everything added in November 2021
References
- ^ Cybersecurity and Infrastructure Security Agency. “Arm Trusted Firmware Out-of-Bounds Write Vulnerability”. Known Exploited Vulnerabilities Catalog, added 3 Nov 2021.
- ^ National Institute of Standards and Technology. “CVE-2021-27562 Detail”. National Vulnerability Database, published 25 May 2021.
- ^ Arm. Advisories and fixes: developer.arm.com.
- ^ FIRST. “Exploit Prediction Scoring System”. EPSS 0.031, percentile 87.6, 31 Oct 2026.
- CVE Program. “CVE-2021-27562”. The official CVE record.
This article is built from CISA’s catalog (version 2026.10.30), NVD’s record and FIRST’s scores, kept in HARD’s database and checked every morning. The plain English is HARD’s.