CVE-2021-27561Known exploitationPublic exploitNetwork attack vector

Unauthenticated root command execution via unsanitized zone parameter

Published Oct 15, 2021 · Updated Oct 21, 2025

OS command injection in Yealink Device Management 3.6.0.20 and earlier allows remote attackers to execute commands as root. fw_restful_service_get inserts the unfiltered zone query value into a firewall-cmd string with snprintf, then passes it through fw_do_cmd to popen. A pre-authentication HTTPS endpoint relays the crafted request to the root smserver daemon, granting full operating-system command execution.

CVSS severity9.8
Critical
EPSS probability82.86%
Next 30 days · Nov 1, 2026
Known exploitationReported
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

OS command injection in Yealink Device Management 3.6.0.20 and earlier allows remote attackers to execute commands as root. fw_restful_service_get inserts the unfiltered zone query value into a firewall-cmd string with snprintf, then passes it through fw_do_cmd to popen. A pre-authentication HTTPS endpoint relays the crafted request to the root smserver daemon, granting full operating-system command execution.

The record

CVE
CVE-2021-27561
Published
Oct 15, 2021
Updated
Oct 21, 2025
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-78, T1059.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Oct 15, 2021CVE publishedPublication date reported by the CVE source.
  2. Oct 21, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

9.8YealinkCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
9.8CISA-ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Activity data is delayed. The latest report is Sep 28, 2026.

Daily unique IPsShadowserver observations through Sep 28, 2026. Gaps indicate unavailable data.
Sep 22, 2026Sep 28, 2026
View daily counts
Reporting dayUnique IPs
Sep 22, 20262
Sep 23, 2026Unavailable
Sep 24, 2026Unavailable
Sep 25, 20261
Sep 26, 20261
Sep 27, 20262
Sep 28, 20261
Latest reporting daySep 28, 2026
Latest daily unique IPs1
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationReported
Public exploitPublished

Weakness, pattern, technique

CWE-78Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection')
T1059.004Command and Scripting Interpreter: Unix Shell

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Reported exploitation

Technologies

Your stack

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Your stack

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