CVE-2025-20736 is a stack-based buffer overflow vulnerability classified under CWE-121, affecting the WLAN AP driver in multiple MediaTek chipsets including MT6890, MT7615, MT7622, MT7663, MT7915, MT7916, MT7981, and MT7986. The root cause is an incorrect bounds check that allows an out-of-bounds write on the stack. This vulnerability can be triggered locally by an attacker who already possesses System-level privileges, enabling them to escalate privileges further or execute arbitrary code with elevated rights. The flaw does not require user interaction, increasing its risk in environments where attackers have some level of system access. Affected firmware versions include SDK release 7.6.7.2 and earlier, as well as openWRT 19.07 and 21.02. The vulnerability impacts confidentiality, integrity, and availability due to the potential for arbitrary code execution or system compromise. Although no active exploits have been reported, the medium CVSS score of 6.7 reflects the significant impact combined with the requirement for high privileges to exploit. The issue was publicly disclosed on November 4, 2025, with MediaTek assigning the patch ID WCNCR00435347 and issue ID MSV-4049. Mitigation relies on applying vendor patches and firmware updates once available.

The vulnerability allows a local attacker with existing System privileges to perform an out-of-bounds write on the stack, potentially leading to escalation of privileges or arbitrary code execution with elevated rights. This can compromise the confidentiality, integrity, and availability of affected devices, particularly wireless access points and embedded systems using the vulnerable MediaTek chipsets. Organizations relying on these chipsets for network infrastructure could face increased risk of persistent compromise or lateral movement within their networks. Although exploitation requires prior System-level access, the flaw could be leveraged by attackers to solidify control or bypass security mechanisms. The absence of user interaction for exploitation increases the risk in automated or unattended environments. The medium severity rating suggests a moderate but significant threat, especially in sensitive or critical infrastructure deployments.

1. Monitor MediaTek’s official channels for the release of patches corresponding to patch ID WCNCR00435347 and apply them promptly to all affected devices. 2. Upgrade firmware to versions beyond SDK release 7.6.7.2 and openWRT versions 19.07 and 21.02 once patched releases are available. 3. Implement strict access controls to limit System-level privileges only to trusted administrators and processes, reducing the likelihood of an attacker gaining the necessary privileges to exploit this vulnerability. 4. Employ runtime protections such as stack canaries, DEP (Data Execution Prevention), and ASLR (Address Space Layout Randomization) where supported by the device firmware to mitigate exploitation impact. 5. Conduct regular security audits and monitoring on devices using these chipsets to detect suspicious local activities indicative of privilege escalation attempts. 6. Consider network segmentation to isolate critical wireless infrastructure, limiting the potential impact of a compromised device. 7. If patching is delayed, consider temporary mitigations such as disabling vulnerable WLAN AP functionalities if feasible without disrupting operations.