CVE-2025-9527 is a high-severity stack-based buffer overflow vulnerability identified in the Linksys E1700 router, specifically version 1.0.0.4.003. The flaw exists within the QoSSetup function, which is accessed via the /goform/QoSSetup endpoint. The vulnerability arises when an attacker manipulates the ack_policy argument, causing a stack-based buffer overflow. This type of overflow can lead to arbitrary code execution or system crashes. The vulnerability is remotely exploitable without requiring user interaction or prior authentication, making it particularly dangerous. The CVSS 4.0 score of 8.7 reflects the ease of exploitation (network vector, low complexity), the lack of required privileges or user interaction, and the high impact on confidentiality, integrity, and availability. Although the vendor was notified early, no response or patch has been issued, increasing the risk for affected users. While no known exploits have been observed in the wild yet, the public availability of an exploit increases the likelihood of imminent attacks. The vulnerability affects a widely deployed consumer and small office router model, which is often used as a gateway device, making exploitation potentially impactful beyond the device itself by enabling network-level compromise or lateral movement.

For European organizations, the impact of this vulnerability can be significant. The Linksys E1700 router is commonly used in small to medium enterprises and home office environments, which are prevalent across Europe. Successful exploitation could allow attackers to execute arbitrary code on the router, leading to full compromise of the device. This could result in interception or manipulation of network traffic, disruption of internet connectivity, and potential pivoting into internal networks. Confidential data could be exposed or altered, and availability of critical network services could be disrupted. Given the lack of vendor response and patch, organizations relying on this device face prolonged exposure. The risk is heightened for organizations with remote or hybrid work setups where these routers serve as primary network gateways. Additionally, the ability to exploit this vulnerability without authentication or user interaction increases the attack surface and ease of compromise, potentially enabling widespread automated attacks targeting vulnerable devices in Europe.

Since no official patch or vendor response is available, European organizations should take immediate and specific steps to mitigate risk. First, identify and inventory all Linksys E1700 routers running version 1.0.0.4.003 within the network. Where possible, replace these devices with updated or alternative router models that have received security patches. If replacement is not immediately feasible, restrict access to the router's management interfaces by implementing network segmentation and firewall rules to block external and unnecessary internal access to the /goform/QoSSetup endpoint. Employ intrusion detection or prevention systems (IDS/IPS) with signatures tuned to detect exploitation attempts targeting this vulnerability. Regularly monitor network traffic for anomalous patterns indicative of exploitation attempts. Disable QoS features if not required, as this may reduce the attack surface. Additionally, consider deploying network-level protections such as VPNs or zero-trust architectures to limit exposure of vulnerable devices. Maintain heightened vigilance for any emerging exploit code or vendor updates and apply patches promptly once available.