# CVE-2025-66738: Yealink T21P_E2 command injection in diagnostic ping function

Source: https://junglewise.ai/threats/cve-2025-66738-yealink-t21p-e2-command-injection-in-diagnostic-ping-function  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2025-12-26. Updated: 2026-07-05  
License: CC BY 4.0 with a link back

CVE-2025-66738 · Severity: high · CVSS 8.8 · Published 2025-12-26

A security vulnerability exists in Yealink T21P_E2 VoIP phones that could allow an authorized user to take full control of the device. By sending a specially crafted request to the phone's diagnostic tools, an attacker can execute unauthorized commands. This could lead to eavesdropping on calls, disruption of phone services, or using the device as a foothold to attack other parts of the corporate network.

Vendors: [Yealink](https://junglewise.ai/threats/vendors/yealink).

## Quick answers

**Is CVE-2025-66738 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2025-66738 being exploited in the wild.

**How severe is CVE-2025-66738?** High severity, with a CVSS score of 8.8, published 26 December 2025.

**Which products and versions are affected?** Yealink T21P E2 IP Phone 52.84.0.15.

**Is there a fix for CVE-2025-66738?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2025-66738 attacked?** It is attacked over the network, in a network appliance.

**Am I affected by CVE-2025-66738?** Check whether you run Yealink Sip-T21\(P\)E2, Yealink Sip-T21\(P\)E2 Firmware or Yealink T21P E2 IP Phone at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

A command injection vulnerability (CWE-77) exists in the Yealink T21P_E2 phone running firmware version 52.84.0.15. The flaw is located within the ping function of the diagnostic component, which fails to properly neutralize special elements in user-supplied input. A remote attacker with 'normal' (low) privileges can exploit this by sending a crafted request to the web management interface. Successful exploitation allows for arbitrary code execution with the privileges of the web service, potentially leading to full system compromise. A proof-of-concept has been identified in public disclosures.

## Affected products

- Yealink T21P_E2 Phone 52.84.0.15

## Timeline

- 2025-12-26: disclosed
- 2025-12-26: advisory

## References

- [https://drive.google.com/file/d/13t5ywSPJMx4487njJcH3ZTNuc_k3h4ty/view?usp=sharing](https://drive.google.com/file/d/13t5ywSPJMx4487njJcH3ZTNuc_k3h4ty/view?usp=sharing)

## Related threats

- [Yealink T21P_E2 directory traversal in diagnostic component](https://junglewise.ai/threats/cve-2025-66737-yealink-t21p-e2-directory-traversal-in-diagnostic-component)