CVE-2026-100740 in DIR-895L
Summary
by MITRE • 09/27/2026
A vulnerability was detected in D-Link DIR-895L A1_102b07. Impacted is the function tunnel_set_params of the file tunnel.c of the component L2TP Control Channel Parser. Performing a manipulation results in out-of-bounds write. The attack may be initiated remotely. The exploit is now public and may be used.
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Analysis
by VulDB Data Team • 09/27/2026
The vulnerability identified within D-Link DIR-895L firmware version A1_102b07 represents a critical security flaw located in the L2TP Control Channel Parser component, specifically affecting the tunnel_set_params function found in the tunnel.c source file. This issue is classified as an out-of-bounds write vulnerability, which falls under the Common Weakness Enumeration category CWE-787: Out-of-bounds Write. Such a defect occurs when software writes data to a memory location beyond the intended buffer boundaries, potentially overwriting adjacent memory structures and leading to unpredictable system behavior or complete compromise of the device's integrity. The presence of this flaw indicates insufficient validation of input parameters passed during the configuration of Layer 2 Tunneling Protocol tunnels, allowing an attacker to manipulate internal state variables in ways that were not anticipated by the developers.
The operational impact of this vulnerability is severe due to its remote exploitability and the public availability of proof-of-concept code. Because the attack can be initiated remotely over a network connection without requiring prior authentication or user interaction, it significantly lowers the barrier for entry for malicious actors. The out-of-bounds write mechanism typically allows an attacker to corrupt memory structures such as function pointers, return addresses, or other critical control data within the device's firmware. This corruption can lead to arbitrary code execution, enabling the attacker to gain full administrative privileges on the router. Once compromised, the device may be used as a pivot point for further attacks against internal network resources, deployed in botnets like Mirai variants that target IoT devices, or utilized to intercept and modify unencrypted traffic traversing the tunnel interface.
From an offensive security perspective, this vulnerability aligns with MITRE ATT&CK techniques related to initial access and privilege escalation via exploited remote services. The public release of exploit code means that automated scanning tools and opportunistic attackers are actively leveraging this flaw against exposed D-Link routers on the internet. This situation highlights a common challenge in IoT device lifecycle management where firmware updates may not promptly address complex memory safety issues embedded deep within protocol parsing logic. The lack of robust bounds checking in the tunnel_set_params function suggests that security testing during development did adequately cover edge cases involving malformed or oversized L2TP control messages, leaving a persistent attack surface for network-based adversaries.
Mitigation strategies must prioritize immediate isolation and patching to prevent exploitation given the active nature of public exploits. Administrators should apply any available firmware updates from D-Link that address this specific CVE if one has been assigned and published. In cases where patches are unavailable or delayed, network segmentation is critical; placing these devices in a separate VLAN with strict firewall rules can limit lateral movement even if the router itself is compromised. Additionally, disabling unnecessary remote management features such as WAN-side access to the administrative interface reduces the attack surface by preventing external actors from reaching vulnerable services directly. Monitoring network traffic for anomalous L2TP control messages or unusual outbound connections originating from the device can also aid in early detection of exploitation attempts while longer-term remediation plans are executed.