Cyber Resilience

CVE-2021-27561

RCE in Yealink Device Management ≤ 3.6.0.20

CISA KEVActive ExploitationEUVD ExploitedRCECommand Injection
Published
15 October 2021
Modified
10 November 2025
KEV Added
03 November 2021
CVSS Score v3.1 9.8
Click a component to see what it means
Raw vectorCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
EPSS Score 0.83 99.6th percentile
Risk Priority 97 floored blend · peak EPSS

Summary

CVE-2021-27561 is a critical-severity OS Command Injection (CWE-78) vulnerability in Yealink Device Management. Its CVSS base score is 9.8 (Critical).

Operationally, exploitation aligns with the MITRE ATT&CK technique Command and Scripting Interpreter (T1059); ranked in the top 0.4% of CVEs by exploit likelihood; CISA has added it to the Known Exploited Vulnerabilities catalog.

Deeper analysis AI-assisted summary

Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.

Yealink Device Management (DM) version 3.6.0.20 contains an unauthenticated command injection vulnerability (CWE-78) that permits arbitrary command execution as root. The flaw is reachable at the /sm/api/v1/firewall/zone/services endpoint and carries a CVSS 3.1 base score of 9.8, reflecting network-accessible exploitation with no required credentials or user interaction.

An attacker with network connectivity to the affected server can submit crafted requests to the vulnerable URI and execute operating-system commands with full root privileges, resulting in complete compromise of confidentiality, integrity, and availability of the Device Management application and its host.

The vulnerability is listed in CISA's Known Exploited Vulnerabilities catalog, indicating confirmed in-the-wild exploitation; the associated SSD Disclosure report provides further technical details on the injection vector. No vendor-supplied patch or mitigation guidance appears in the supplied references.

OWASP Top 10 for Web (2025)

A05:2025 Injection

EU & UK References

Vulnerability Data

Yealink Device Management (DM) 3.6.0.20 allows command injection as root via the /sm/api/v1/firewall/zone/services URI, without authentication.

CWE(s)
CWE-78
KEV Date Added
03 November 2021

Related Threats

MITRE ATT&CK Enterprise Techniques

T1059 Command and Scripting Interpreter Execution
Adversaries may abuse command and script interpreters to execute commands, scripts, or binaries.
attack.mitre.org →
T1059.003 Windows Command Shell Execution
Adversaries may abuse the Windows command shell for execution.
attack.mitre.org →
T1059.004 Unix Shell Execution
Adversaries may abuse Unix shell commands and scripts for execution.
attack.mitre.org →
T1059.001 PowerShell Execution
Adversaries may abuse PowerShell commands and scripts for execution.
attack.mitre.org →
T1190 Exploit Public-Facing Application Initial Access
Adversaries may attempt to exploit a weakness in an Internet-facing host or system to initially access a network.
attack.mitre.org →
Derived from this CVE’s CWE(s) via the direct CWE→ATT&CK cross-walk.

CVEs Like This One

CVE-2023-43959Same vendor: Yealink
CVE-2023-39780Shared CWE-78both on KEV
CVE-2021-20035Shared CWE-78both on KEV
CVE-2026-39808Shared CWE-78both on KEV
CVE-2023-49897Shared CWE-78both on KEV
CVE-2024-6047Shared CWE-78both on KEV
CVE-2024-40890Shared CWE-78both on KEV
CVE-2025-48703Shared CWE-78both on KEV
CVE-2024-9463Shared CWE-78both on KEV
CVE-2019-17621Shared CWE-78both on KEV

Affected Assets

yealink
device management
≤ 3.6.0.20

Mitigating Controls

Control response

Prevent
Stop it (NIST 800-53)

—

Detect
Catch it (NIST detect / respond)

—

Harden
Shrink the surface (DISA STIG)

—

Validate
Prove the fix (OWASP ASVS)
  • V1.2.5
  • V1.2.8
  • V15.2.5

Likely Mitigating Controls AI

Per-CVE control mapping for this CVE has not run yet; the list below is derived from the weakness types (CWEs) cited in the NVD entry.

SC-27 Platform-independent Applications
addresses: CWE-78

Platform-independent apps typically execute inside a managed runtime or sandbox that restricts direct OS command execution, reducing the ability to exploit OS command injection.

SI-10 Information Input Validation
addresses: CWE-78

Validates inputs to block special elements that would alter OS command execution.

Mitigating Controls (NIST CSF 2.0) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.

PR.PS-06 mostly match
prevents

PR.PS-06's SDLC practices directly require secure coding and input handling that blocks command-injection defects, yet the single broad outcome leaves many specific neutralization vectors and verification gaps unaddressed.

PR.PS-02 partial match
prevents

Routine patching/maintenance can remediate known command-injection CVEs in dependencies (partial forward) but does nothing to stop developers from introducing improper neutralization in custom code (none reverse).

Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.

A.8.29 Security testing in development and acceptance mostly match
finds

Security testing and code review target insecure use of operating-system command interfaces, catching command-injection flaws introduced during development.

References