CVE-2021-28839 in DAP-2310
Summary
by MITRE • 08/11/2021
Null Pointer Dereference vulnerability exists in D-Link DAP-2310 2.07.RC031, DAP-2330 1.07.RC028, DAP-2360 2.07.RC043, DAP-2553 3.06.RC027, DAP-2660 1.13.RC074, DAP-2690 3.16.RC100, DAP-2695 1.17.RC063, DAP-3320 1.01.RC014 and DAP-3662 1.01.RC022 in the upload_certificate function of sbin/httpd binary. When the binary handle the specific HTTP GET request, the strrchr in the upload_certificate function would take NULL as first argument, and incur the NULL pointer dereference vulnerability.
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Analysis
by VulDB Data Team • 08/15/2021
The vulnerability identified as CVE-2021-28839 represents a critical null pointer dereference flaw within the web interface of multiple D-Link wireless access point models including DAP-2310, DAP-2330, DAP-2360, DAP-2553, DAP-2660, DAP-2690, DAP-2695, DAP-3320, and DAP-3662. This issue manifests specifically within the sbin/httpd binary's upload_certificate function, where the application fails to properly validate input parameters before processing HTTP GET requests. The vulnerability stems from the improper handling of string operations, particularly the strrchr function which is designed to search for the last occurrence of a character in a string but receives a NULL pointer as its first argument. This flaw falls under the CWE-476 category of NULL Pointer Dereference, a well-documented weakness that occurs when an application attempts to access memory through a null pointer reference, leading to immediate program termination or potential system instability. The affected devices operate with firmware versions ranging from RC027 to RC100, indicating this vulnerability has persisted across multiple firmware releases and affects a broad range of enterprise and consumer networking equipment.
The operational impact of this vulnerability extends beyond simple service disruption to potentially enable remote code execution or denial of service attacks. When an attacker crafts a specific HTTP GET request that triggers the upload_certificate function, the application's failure to validate the input string before passing it to strrchr results in a null pointer dereference that crashes the httpd service. This behavior aligns with ATT&CK technique T1210 - Exploitation of Remote Services, where adversaries exploit weaknesses in network services to gain unauthorized access or cause system instability. The vulnerability's presence in the web server component of these access points means that any remote user with network access could potentially trigger the crash, leading to denial of service for legitimate users and potentially providing an entry point for more sophisticated attacks. The fact that multiple models across different firmware versions contain this flaw suggests a systemic issue in the software development lifecycle, particularly in input validation and error handling procedures.
Mitigation strategies for CVE-2021-28839 should prioritize immediate firmware updates from D-Link, as the vendor has likely released patches addressing this specific null pointer dereference issue. Network administrators should implement network segmentation to limit access to these devices and restrict HTTP traffic to only trusted administrative networks. Additionally, monitoring for suspicious HTTP GET requests that may trigger the vulnerability should be enabled through network intrusion detection systems. The vulnerability's nature makes it particularly attractive to attackers who may attempt to exploit it for persistent access or to establish a foothold within network infrastructure. Security teams should consider implementing automated vulnerability scanning to identify affected devices within their network and establish a remediation timeline that accounts for the critical nature of this flaw. The remediation process should include not only firmware updates but also verification that the updated systems properly handle malformed HTTP requests without crashing. Organizations should also review their network access controls to ensure that only authorized personnel can access the administrative interfaces of these devices, as the vulnerability could potentially be exploited by attackers who gain access to the network through other means.