CVE-2026-86509 in DIR-895L
Summary
by MITRE • 09/08/2026
A flaw has been found in D-Link DIR-895L A1_102b07. This impacts the function sendOffer/sendACK of the file udhcpcd/serverpacket.c of the component udhcpcd. This manipulation causes stack-based buffer overflow. The attack can only be done within the local network. The exploit has been published and may be used.
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Analysis
by VulDB Data Team • 09/08/2026
The vulnerability identified in D-Link DIR-895L router firmware version A1_102b07 represents a critical security flaw located within the udhcpcd component, specifically affecting the serverpacket.c source file. This daemon is responsible for handling Dynamic Host Configuration Protocol (DHCP) operations on the device, which are fundamental to network connectivity as they allow devices to automatically obtain IP addresses and other configuration parameters from a DHCP server or client. The specific functions impacted by this flaw are sendOffer and sendACK, which are used when the router acts in a capacity that involves offering an IP address lease or acknowledging such a lease to a requesting host. These operations require the construction of network packets containing variable-length data fields derived from user-controlled inputs or external network sources.
The core technical issue is a stack-based buffer overflow resulting from improper bounds checking during the processing of these DHCP messages. When the udhcpcd service processes incoming requests that trigger the sendOffer or sendACK routines, it fails to adequately validate the length of specific data fields before copying them into fixed-size buffers allocated on the program's call stack. This lack of validation allows an attacker to supply a payload exceeding the buffer capacity, thereby overwriting adjacent memory locations on the stack. In C-based embedded systems like this router firmware, such overflow conditions are particularly dangerous because they can overwrite critical control data including return addresses and saved frame pointers. By carefully crafting the malicious DHCP packet, an attacker can manipulate these overwritten values to redirect program execution flow toward injected shellcode or existing library functions within the device's memory space.
The operational impact of this vulnerability is severe, as it potentially allows for arbitrary code execution with the privileges of the udhcpcd process. Given that network daemons often run with elevated permissions to facilitate configuration changes and packet forwarding, successful exploitation could grant an attacker full control over the router. This compromises not only the integrity of the device itself but also the security of all devices connected to it behind the NAT firewall. An attacker can use this access to intercept traffic, perform man-in-the-middle attacks, redirect users to malicious sites, or pivot into other segments of the local network. The vulnerability is classified under CWE-121, which denotes a stack-based buffer overflow, highlighting the fundamental memory safety error in the software development lifecycle that led to its creation.
From an offensive security perspective, this flaw aligns with MITRE ATT&CK techniques related to initial access and execution within a local network environment. Specifically, it relates to exploitation of remote services where the attacker leverages a vulnerable application layer protocol to gain foothold on the target system. The fact that the exploit has been published significantly increases the risk landscape, as automated tools or less sophisticated threat actors can now leverage this knowledge without needing to reverse engineer the binary themselves. This lowers the barrier to entry for attacks targeting these specific router models, making them prime candidates for botnet recruitment or localized network compromise campaigns.
Mitigation strategies must address both immediate remediation and long-term security posture improvements. The primary defense is applying the latest firmware updates provided by D-Link that patch this buffer overflow condition through proper input validation and bounds checking in the udhcpcd component. If an update is not immediately available, administrators should consider isolating affected devices on a separate VLAN with strict access control lists to limit lateral movement potential. Additionally disabling unnecessary services such as UPnP or remote management interfaces can reduce the attack surface. Network monitoring solutions should be configured to detect anomalous DHCP traffic patterns indicative of exploitation attempts, although given the nature of stack overflows, behavioral detection may be challenging without deep packet inspection capabilities specifically tuned for this vulnerability signature.