CVE-2021-29296 in DIR-825
Summary
by MITRE • 08/11/2021
Null Pointer Dereference vulnerability in D-Link DIR-825 2.10b02, which could let a remote malicious user cause a denial of service. The vulnerability could be triggered by sending an HTTP request with URL /vct_wan; the sbin/httpd would invoke the strchr function and take NULL as a first argument, which finally leads to the segmentation fault. NOTE: The DIR-825 and all hardware revisions is considered End of Life and as such this issue will not be patched
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Analysis
by VulDB Data Team • 06/05/2024
The CVE-2021-29296 vulnerability represents a critical null pointer dereference flaw discovered in D-Link DIR-825 router firmware version 2.10b02, with the affected device being part of the end-of-life product line. This vulnerability stems from improper input validation within the web server component of the router's firmware, specifically within the sbin/httpd binary that handles incoming HTTP requests. The flaw manifests when a remote attacker sends a specially crafted HTTP request to the specific URL path /vct_wan, which triggers a chain of function calls that ultimately results in a segmentation fault and subsequent system crash. The vulnerability is classified as a classic null pointer dereference according to CWE-476, which occurs when a program attempts to access memory through a null pointer reference, leading to an immediate system termination.
The technical execution of this vulnerability involves the exploitation of a function call sequence where the strchr function receives a NULL pointer as its first argument, violating fundamental programming safety principles and causing an immediate segmentation fault. This particular implementation flaw demonstrates poor error handling and input validation practices, as the web server component fails to properly validate or sanitize incoming URL parameters before passing them to underlying string manipulation functions. The vulnerability is categorized under the ATT&CK technique T1499.004 for Network Denial of Service, as it allows remote attackers to disrupt service availability by causing the router to crash and become unresponsive. The affected system architecture processes HTTP requests through a web server daemon that lacks proper null pointer checks, creating an exploitable condition that can be triggered without authentication or privilege requirements.
The operational impact of this vulnerability extends beyond simple denial of service, as it represents a fundamental flaw in the router's security architecture that could be leveraged in larger attack campaigns. When exploited, the vulnerability causes the router to crash and restart, effectively creating a persistent availability issue that can disrupt network connectivity for all devices relying on that router for internet access. Network administrators and security professionals should recognize this vulnerability as a critical issue in legacy networking equipment, particularly in environments where older D-Link devices remain operational despite end-of-life status. The vulnerability's exploitation requires minimal technical expertise and can be automated, making it particularly dangerous in environments where such devices are not regularly monitored or updated. Given that the device is end-of-life, there are no official patches or firmware updates available to address this specific flaw, leaving affected organizations with limited remediation options.
Organizations affected by this vulnerability should implement immediate network segmentation strategies to isolate potentially vulnerable devices, deploy network monitoring solutions to detect anomalous HTTP traffic patterns, and consider hardware replacement as the most effective long-term solution. The vulnerability serves as a prime example of why end-of-life device management is critical in cybersecurity operations, as legacy systems often contain unpatched vulnerabilities that can be exploited by threat actors. Security teams should also consider implementing intrusion detection systems that can identify and alert on requests to the specific vulnerable URL path /vct_wan, providing an additional layer of protection against exploitation attempts. Organizations should conduct comprehensive inventory audits to identify all instances of this vulnerable device model, as the end-of-life status does not prevent these devices from remaining operational in various network environments where they may be overlooked during security assessments.