Threats / Yealink / CVE-2021-27561
CVE-2021-27561
· EUVD no mirror located
· GCVE no mirror located
Verified 2026-08-04
Yealink Device Management vulnerability
Yealink Device Management contains an unauthenticated server-side request forgery vulnerability enabling remote code execution on affected systems.
Verdict
Today item — known-exploited.
An unauthenticated attacker can exploit SSRF in Yealink Device Management to execute arbitrary code. The high EPSS score and active exploitation in the wild indicate immediate risk to unpatched deployments.
CISA KEV Yes · 2021-11-034EPSS 0.82516 (verify live)5CVSS 9.8 (CISA)3CISA SSVC Exploitation: active · Automatable: yes · Impact: total3Exploit Public PoC / detection · nuclei template11
01
Is it exploitable?
— the evidence, ranked above the scoreReported exploitation
528 independent public reports of in-the-wild exploitation are cataloged.Distinct reporting sources (vendor, incident response, government); open them for the underlying claims.
Exploited in the wild
Listed in the CISA Known Exploited Vulnerabilities catalog (added 2021-11-03).
Probability (EPSS)
EPSS 0.82516 — modeled likelihood of exploitation activity.EPSS is a daily-changing model output — open the source for today's value.
Severity / affected
CVSS 9.8 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H) · Affected: Yealink, Device Management. Confirm exact fixed builds in the vendor advisory.CVSS — CISA-assigned via the ADP container (CVE.org), version 3.1; the CNA left no metrics, so CISA's own score is used ahead of NVD.
Weakness (CWE)
Mapped to CWE-78 OS Command Injection — weakness family: Injection.CWE assignment from the public NVD record (may be stale); the weakness class drives how the flaw is exploited.
CISA SSVC (triage disposition)
Exploitation: active · Automatable: yes · Technical Impact: totalCISA's own stakeholder-specific triage inputs, published in the CVE record (CISA Coordinator role). NOTE: this is CISA's three decision points; the final Act/Attend/Track decision also requires a Mission & Well-being input not published here, so no overall decision is asserted.
Currency of the record
CISA added this to its KEV catalog 19 days after the CVE record was published.KEV lag = CISA-KEV dateAdded − CVE.org datePublished; a floor on how long the known-exploited flaw sat in the public record before the federal catalog listed it. Severity/weakness here is CNA- or CISA-assigned (current at disclosure), independent of NVD's analysis backlog.
Public exploit available
Public exploit tooling is catalogued for this CVE (a public proof-of-concept / detection template). Catalog entries: nuclei template. We link the catalog page(s) only — no payload or code is hosted or restated here.Link, never host — the catalog page is the source; basicsecurity.net does not redistribute payloads.
02
Who’s exploiting it?
— attribution turns risk into urgencyAttribution not established
No confirmed (advisory-backed) threat-actor attribution is established for this record. Absence of a named actor is not absence of compromise — see Coverage & confidence.
03
Why it matters
— the attack path, told twice: adversary, then board1
Front door — unauthenticated access narrative 1
Attacker
I craft a malicious request that exploits the SSRF flaw to make the server perform unintended internal requests.
Business
Attackers gain initial access to the management infrastructure without authentication, bypassing security perimeter controls.
2
Keys to the kingdom — privilege/identity takeover narrative 2
Attacker
I leverage the SSRF to access internal services or metadata endpoints that grant me elevated privileges or credentials.
Business
Lateral movement becomes possible across the managed device ecosystem, expanding the attack surface.
3
Lateral reach — past segmentation narrative 3
Attacker
I execute arbitrary system commands through the compromised management server to establish persistent control.
Business
Full compromise of the Device Management platform enables command and control of all connected Yealink devices.
4
Data at risk — exfiltration narrative 4
Attacker
I deploy malware or firmware modifications across the managed device fleet for long-term persistence.
Business
Communications infrastructure is compromised, risking data interception, call manipulation, and operational disruption.
04
What to do
— defensible action- Remediate per the vendor advisory — confirm the fixed build for your version and verify exposure.1
Say it to the boardA vulnerability with this evidence profile is a defensible budget line, not a backlog ticket — fund the change against the proof above.
05