CVE-2025-20657 is a medium-severity vulnerability classified as an out-of-bounds write (CWE-787) in the video decoder (vdec) component of various MediaTek System on Chips (SoCs), including MT6765, MT6768, MT6781, MT6789, MT6833, MT6853, MT6877, MT6885, MT8768, MT8771, MT8781, MT8786, and MT8791T. The root cause is improper input validation within the vdec module, which can lead to a permission bypass scenario. This flaw allows an attacker who already possesses System-level privileges on the device to escalate their privileges further, potentially gaining unauthorized access to sensitive system functions or data. The vulnerability affects Android versions 12.0 through 15.0 running on these MediaTek platforms. Exploitation does not require user interaction, but the attacker must have high privileges (System) to begin with, which limits the initial attack surface but raises concerns about post-compromise escalation. The CVSS 3.1 base score is 6.7, reflecting a medium severity with high impact on confidentiality, integrity, and availability. No public exploits or active exploitation have been reported to date. The vulnerability was reserved in November 2024 and published in April 2025. MediaTek has assigned a patch ID (ALPS09486425) and issue ID (MSV-2609) for remediation, though no direct patch links are currently available. This vulnerability highlights the importance of robust input validation in multimedia processing components, which are often complex and privileged parts of mobile device firmware.

The primary impact of CVE-2025-20657 is local privilege escalation on devices using affected MediaTek SoCs running Android 12 to 15. An attacker who has already compromised a device to the System privilege level can exploit this vulnerability to bypass permission checks and gain even higher privileges, potentially leading to full device compromise. This could allow unauthorized access to sensitive user data, modification or deletion of critical system files, installation of persistent malware, or disruption of device functionality. Since the vulnerability affects widely deployed MediaTek chipsets commonly found in mid-range and budget smartphones globally, a large number of consumer devices are at risk. Enterprises relying on such devices for mobile workforce operations could face increased risk of data breaches or device manipulation. The lack of required user interaction facilitates stealthy exploitation post-compromise. Although no exploits are known in the wild, the vulnerability's presence in core multimedia processing components makes it attractive for attackers seeking to maintain persistence or evade detection. Overall, the threat could undermine device security, user privacy, and trust in affected mobile platforms.

To mitigate CVE-2025-20657, organizations and users should: 1) Apply official security patches from device manufacturers or MediaTek as soon as they become available, referencing patch ID ALPS09486425 and issue ID MSV-2609. 2) Monitor vendor advisories and update Android OS versions on affected devices promptly to incorporate fixes. 3) Limit the number of applications and processes granted System-level privileges to reduce the risk of initial compromise that could lead to exploitation. 4) Employ mobile device management (MDM) solutions to enforce security policies and restrict installation of untrusted apps that might escalate privileges. 5) Use runtime protection and behavioral monitoring tools to detect anomalous activities indicative of privilege escalation attempts. 6) For organizations deploying custom ROMs or firmware, ensure that the vdec component is updated and input validation is enforced rigorously. 7) Educate users about the risks of rooting or jailbreaking devices, which can increase exposure to such vulnerabilities. 8) Conduct regular security audits and penetration testing focused on privilege escalation vectors in mobile environments. These targeted actions go beyond generic advice by focusing on controlling System privilege access and ensuring timely patch deployment on affected MediaTek platforms.