Security readout for executives and security teams
Plain-English summary
Yealink Device Management 3.6.0.20 has an unauthenticated root-level command injection flaw. An internet-reachable management server could let an attacker fully control the system. CISA lists this CVE in KEV, so treat exposure as urgent rather than theoretical.
Executive priority
Prioritize within emergency remediation workflows. This is a remotely reachable, unauthenticated root command injection vulnerability with known exploitation evidence from CISA KEV.
Technical view
CVE-2021-27561 is CWE-78 command injection in Yealink DM 3.6.0.20 via the /sm/api/v1/firewall/zone/services URI. The CVSS 3.1 score is 9.8, with network access, low complexity, no privileges, and no user interaction required.
Likely exposure
Exposure is most likely where Yealink Device Management is deployed and reachable from untrusted networks. The source bundle identifies version 3.6.0.20, but does not provide a complete affected-version matrix or CPE list.
Exploitation context
CISA KEV inclusion supports known exploitation. The provided sources do not describe attacker campaigns, exploit volume, or post-exploitation behavior. Because exploitation requires no authentication and can execute as root, exposed systems should be assumed high-risk.
Researcher notes
Evidence supports critical severity and exploited status. Patch details, full version range, and vendor remediation specifics are not present in the supplied bundle, so validation should stay focused on confirmed Yealink DM exposure and official guidance.
Mitigation direction
- Identify all Yealink Device Management deployments and versions.
- Remove Yealink DM from direct internet exposure immediately.
- Restrict access to trusted administrative networks only.
- Check Yealink or official vendor guidance for fixed versions or mitigations.
- Investigate exposed systems for compromise before returning them to service.
Validation and detection
- Confirm whether Yealink DM 3.6.0.20 is deployed.
- Review firewall and external exposure records for Yealink DM services.
- Check logs for requests to /sm/api/v1/firewall/zone/services.
- Verify access controls block unauthenticated external access.
- Document vendor guidance status and remediation evidence.
Michael Williams reviewed this cited source version on .
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-78: Command execution behavior lookup
Command injection weaknesses can lead defenders to review execution techniques and command interpreter telemetry. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupExecution behavior lookup
The CVE wording references code or command execution, so execution technique review may help defensive triage. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.
Open ATT&CK lookupCVE-2021-27561 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- Critical
- CVSS
- 9.8 (3.1)
- Known Exploited
- Yes
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CISA KEV status
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H3.95.9Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
9.8CriticalVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Source materials
- CVE List V5 sourceCVE List V5
- https://ssd-disclosure.com/?p=4688CVE reference · x_refsource_MISC
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-27561CVE reference · government-resource
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.