Security Resilience

CVE-2025-66738

RCE in Yealink Sip-T21\(P\)E2 Firmware 52.84.0.15

Public PoCRCECommand Injection
Published
26 December 2025
Modified
07 October 2026
CVSS Score v3.1 8.8
Click a component to see what it means
Raw vectorCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
EPSS Score 0.0063 50th percentile
Risk Priority 65 floored blend · peak EPSS

CVSS and EPSS are reproduced from their sources (NVD, FIRST EPSS). Risk Priority is our own derived reading, not an NVD score.

Summary

CVE-2025-66738 is a high-severity Command Injection (CWE-77) vulnerability in Yealink Sip-T21\(P\)E2 Firmware. Its CVSS base score is 8.8 (High).

Operationally, ranked at the 50th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.

The strongest mitigations our analysis identified map to SA-11 (Developer Testing and Evaluation) and SI-10 (Information Input Validation) — see the control section below for these in your framework.

OWASP Top 10 for Web (2025)

A05:2025 Injection

EU & UK References

Vulnerability Data

An issue in Yealink T21P_E2 Phone 52.84.0.15 allows a remote normal privileged attacker to execute arbitrary code via a crafted request the ping function of the diagnostic component.

CWE(s)
CWE-77

Related Threats

CVEs Like This One

CVE-2025-66737Same product: Yealink Sip-T21\(P\)E2
CVE-2024-28442Same vendor: Yealink
CVE-2024-31747Same vendor: Yealink
CVE-2023-43959Same vendor: Yealink
CVE-2024-24091Same vendor: Yealink
CVE-2024-48353Same vendor: Yealink
CVE-2021-27561Same vendor: Yealink
CVE-2024-24681Same vendor: Yealink
CVE-2024-48352Same vendor: Yealink
CVE-2024-30939Same vendor: Yealink

Affected Assets

yealink
sip-t21\(p\)e2 firmware
52.84.0.15

Mitigating Controls

Mitigating Controls (NIST 800-53 r5) AI

SA-11 Developer Testing and Evaluation good match

Developer testing and evaluation can discover command-construction flaws before deployment.

SI-10 Information Input Validation good match

Input validation directly stops construction of commands from untrusted data containing special elements.

SA-8 Security and Privacy Engineering Principles partial match

Secure engineering principles include proper neutralization and safe command construction practices.

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 in development catches command-injection vulnerabilities before release.

A.8.28 Secure coding partial match
prevents

Secure coding standards require proper escaping and parameterization of commands, directly eliminating CWE-77.

Hardening callouts derived

DISA STIG baselines are authored against specific weaknesses. Where this CVE cites a broad weakness class, the mapping is not asserted at that abstraction (owner ruling, 2026-09-25: grade only at Base and below), so no rule is shown here rather than a rule shown against the wrong grain.

  • No fine-grained STIG row for CWE-77, a class-level weakness, and none of its children carries one either.

References