CVE-2026-12220 is a stack-based buffer overflow vulnerability affecting Yealink SIP-T46U firmware version 108.86.0.118. The issue arises from improper handling of the uid argument in the mod_upgrade.SparePartsUpload function of the Firmware Chunk Upload handler (/api/upgrade/accupgradebychunk). This flaw allows an attacker with local network access to cause a buffer overflow, potentially leading to arbitrary code execution or denial of service. The vulnerability has been publicly disclosed, but the vendor has not issued any response or patch. The CVSS 4.0 score is 8.6, indicating high severity with attack vector limited to adjacent network, low attack complexity, no privileges required beyond local network, and no user interaction needed.

Successful exploitation of this vulnerability could allow an attacker on the local network to cause a stack-based buffer overflow on the affected device. This may lead to arbitrary code execution or device crash, impacting availability and potentially confidentiality and integrity of the device. Since the attack requires local network access, remote exploitation over the internet is not feasible without additional network access.

No official patch or remediation is currently available from the vendor, as they have not responded to the disclosure. Users should restrict local network access to the affected device and monitor for suspicious activity. Consider network segmentation or limiting access to trusted users until a vendor fix is released. Patch status is not yet confirmed — check the vendor advisory for current remediation guidance.