A critical zero-day vulnerability, designated as CVE-2025-9961, has been identified in TP-Link routers, posing significant security risks to users. This flaw allows attackers to execute arbitrary code remotely, potentially compromising the entire network.
Technical Details of the Vulnerability
The vulnerability resides within the router’s Customer Premises Equipment (CPE) WAN Management Protocol (CWMP) binary, a component of the TR-069 protocol used by service providers for remote device management. Specifically, it is a stack-based buffer overflow in the `cwmp` process. By sending a specially crafted request, attackers can overwrite the program counter (PC), seizing control of the execution flow.
Address Space Layout Randomization (ASLR) is a security feature designed to prevent such exploits by randomizing memory addresses. However, in this case, researchers at ByteRay discovered that ASLR could be bypassed through a brute-force strategy. By repeatedly guessing the base address of the standard C library (`libc`), they located the `system()` function without needing an information leak to disclose memory layouts.
An incorrect guess would crash the `cwmp` service. However, if the attacker has access to the TP-Link web panel, they can restart the service, making the brute-force attack practical.
Exploit Methodology
The attack requires the router to be configured to accept the attacker’s custom Auto Configuration Server (ACS). The exploit is delivered through a `SetParameterValues` request containing the payload. The final payload employs a return-to-libc (`ret2libc`) technique to call the `system()` function with a command argument. This command instructs the router to download and execute a malicious binary, such as a reverse shell, from an attacker-controlled server, granting the attacker complete remote access.
Discovery and Proof-of-Concept Release
The ByteRay research team discovered this vulnerability and released a proof-of-concept (PoC) exploit to demonstrate its severity. During their analysis, they encountered issues with the standard GenieACS platform corrupting the binary payload, preventing successful exploitation. This led them to develop a custom ACS emulator capable of faithfully transmitting the exploit code.
The team has published a detailed technical write-up and the full exploit code on GitHub. They emphasize that the release is intended for educational purposes and security research, allowing administrators to test their own devices. Unauthorized use of other systems is illegal.
Implications and Recommendations
This vulnerability is critical, as successful exploitation allows for complete remote code execution on the router. An attacker could intercept traffic, launch further attacks on the local network, or enlist the device in a botnet. The research underscores the security risks associated with network-facing management protocols like TR-069, where even minor parsing errors can escalate into severe threats.
The exploit highlights that security mitigations like ASLR can sometimes be bypassed with creative attack strategies.
Users of TP-Link routers are advised to monitor for firmware updates from the vendor and apply them as soon as they become available to patch this vulnerability.
