CVE-2025-13735 is an out-of-bounds read vulnerability categorized under CWE-125, found in the ASR Lapwing_Linux operating system used by ASR1903 and ASR3901 devices. The vulnerability resides in the nr_fw kernel modules, specifically in the NrCgi.C source code, which handles certain network-related firmware functions. An out-of-bounds read occurs when the program reads data beyond the allocated buffer boundaries, potentially exposing sensitive memory contents or causing undefined behavior. This flaw can be triggered remotely over the network (AV:N) with low attack complexity (AC:L) and requires low privileges (PR:L) but no user interaction (UI:N). The scope is changed (S:C), meaning exploitation can affect resources beyond the vulnerable component. The impact includes partial loss of confidentiality, integrity, and availability (C:L/I:L/A:L), indicating that attackers may read sensitive data, alter some system states, or cause disruptions. The vulnerability affects all versions of Lapwing_Linux prior to 2025/11/26, with no patches currently available and no known exploits in the wild. The vulnerability's presence in network infrastructure devices makes it a critical concern for organizations relying on ASR hardware for routing or firewalling functions.

For European organizations, especially those in telecommunications, critical infrastructure, and large enterprises using ASR Lapwing_Linux devices, this vulnerability poses risks of sensitive data exposure and potential service interruptions. Attackers exploiting this flaw could read memory contents beyond intended limits, potentially leaking credentials, configuration data, or other sensitive information. The partial integrity and availability impacts suggest attackers might also cause system instability or degrade network services, leading to operational disruptions. Given the network-accessible nature of the vulnerability and low privilege requirements, attackers could leverage this flaw to escalate privileges or move laterally within networks. This is particularly concerning for European telecom operators and ISPs that deploy ASR1903 and ASR3901 devices in their core or edge network infrastructure, as exploitation could impact large user bases and critical communications. The absence of patches increases the window of exposure, necessitating immediate risk management actions.

1. Implement strict network segmentation to isolate ASR Lapwing_Linux devices from untrusted networks and limit access to management interfaces. 2. Enforce strong access controls and authentication mechanisms on devices to restrict low-privilege network access. 3. Monitor network traffic and device logs for unusual or anomalous activity that could indicate exploitation attempts, focusing on the nr_fw module interactions. 4. Coordinate with ASR vendor support channels to obtain early patch releases or workarounds as soon as they become available. 5. Apply virtual patching via intrusion prevention systems (IPS) to detect and block attempts to exploit out-of-bounds read patterns targeting NrCgi.C functionality. 6. Conduct regular vulnerability assessments and penetration testing focused on ASR devices to identify potential exploitation vectors. 7. Prepare incident response plans specific to network device compromise scenarios to minimize impact if exploitation occurs. 8. Limit exposure by disabling unnecessary services or features on affected devices that interact with the vulnerable module.