Security Resilience

CVE-2025-66737

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

Public PoCPath Traversal
Published
26 December 2025
Modified
13 October 2026
CVSS Score v3.1 4.3
Click a component to see what it means
Raw vectorCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
EPSS Score 0.0066 51th percentile
Risk Priority 38 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-2025-66737 is a medium-severity Relative Path Traversal (CWE-23) vulnerability in Yealink Sip-T21\(P\)E2 Firmware. Its CVSS base score is 4.3 (Medium).

Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked in the top 49% of CVEs by exploit likelihood; 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 SI-10 (Information Input Validation) and AC-3 (Access Enforcement) — see the control section below for these in your framework.

OWASP Top 10 for Web (2025)

A01:2025 Broken Access Control

EU & UK References

Vulnerability Data

Yealink T21P_E2 Phone 52.84.0.15 is vulnerable to Directory Traversal. A remote normal privileged attacker can read arbitrary files via a crafted request result read function of the diagnostic component.

CWE(s)
CWE-23

Related Threats

MITRE ATT&CK Enterprise Techniques

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 →
T1210 Exploitation of Remote Services Lateral Movement
Adversaries may exploit remote services to gain unauthorized access to internal systems once inside of a network.
attack.mitre.org →
T1687 Exploitation for Defense Impairment Defense Impairment
Adversaries may exploit vulnerabilities in security software, infrastructure, or defensive components to degrade, disable, or otherwise continue to impair their ability to prevent, detect, or respond to malicious activity.
attack.mitre.org →
Derived from this CVE’s CWE(s) via the direct CWE→ATT&CK cross-walk.

CVEs Like This One

CVE-2025-66738Same product: Yealink Sip-T21\(P\)E2
CVE-2026-84939Shared CWE-23
CVE-2026-31831Shared CWE-23
CVE-2026-50016Shared CWE-23
CVE-2026-20078Shared CWE-23
CVE-2025-58456Shared CWE-23
CVE-2025-32137Shared CWE-23
CVE-2025-58463Shared CWE-23
CVE-2026-83873Shared CWE-23
CVE-2026-5422Shared CWE-23

Affected Assets

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

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)
  • V5.3.2

Mitigating Controls (NIST 800-53 r5) AI

SI-10 Information Input Validation good match

Explicit validation of path inputs stops .. sequences from ever being interpreted by the file system.

AC-3 Access Enforcement partial match

Access enforcement directly blocks unauthorized file reads/writes that result from unresolved .. sequences.

AC-4 Information Flow Enforcement partial match

Information-flow rules can be configured to reject traversals that would move data outside an approved directory boundary.

AC-6 Least Privilege partial match

Least privilege reduces the set of reachable files even when a traversal succeeds.

SA-8 Security and Privacy Engineering Principles partial match

Secure-engineering principles require safe pathname construction and input neutralization before any file operation.

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
blocks

Secure SDLC practices directly require input validation and path sanitization that prevent relative traversal.

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 path traversal via static/dynamic analysis, but does not itself implement the fix.

A.8.28 Secure coding partial match
prevents

Secure coding standards require neutralizing path traversal sequences, directly addressing CWE-23.

References