IoT Inspector Research Lab Security Advisory IOT-20210311-0 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ title: Authenticated Command Injection in D-Link DIR-3060 Web Interface vendor/product: D-Link DIR-3060 (https://www.dlink.com/) vulnerable version: v1.11b04 & Below fixed version: v1.11b04 Hotfix 2 CVE number: CVE-2021-28144 impact: 8.8 (high) CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H reported: 2020-11-27 publication: 2021-03-11 by: T Shiomitsu, IoT Inspector Research Lab https://www.iot-inspector.com/ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Vendor description: ------------------- D-Link Corporation is a Taiwanese multinational networking equipment manufacturing corporation. The DIR-3060 (also known as the EXO AC3000 Smart Mesh Wi-Fi Router) is one of their higher-end home/small business routers. Vulnerability overview/description: ----------------------------------- The D-Link DIR-3060 is affected by a post-authentication command injection vulnerability. Any person who is able to gain authenticated access to a DIR-3060 would be able to run arbitrary system commands on the device as the system "admin" user, with root privileges. Proof of concept: ----------------- When a SOAP request is made to the SetVirtualServerSettings SOAP endpoint, the function at 00461918 in prog.cgi is invoked. This function traverses the SOAP XML request body, stores expected SOAP field values, and takes different paths depending on the values. If a request with a non-null LocalIPAddress, Enabled set to true, an InternalPort of 9 and a ProtocolType of UDP is sent, the function CheckArpTables (named by me, based at 0046163c) is invoked. // ...snip iVar5 = strcmp(Enabled,"true"); if ((((iVar5 == 0) && (LocalIPAddress != (char *)0x0)) && (iVar5 = strcmp(InternalPort,"9"), iVar5 == 0)) && (iVar5 = strcmp(ProtocolType,"UDP"), iVar5 == 0)) { local_4154 = local_4154 + 1; iVar5 = CheckArpTables(LocalIPAddress, InternalPort, ProtocolType, 0xdc, local_4154); if (iVar5 == -1) { local_4160 = 0xb; goto LAB_00462504; } } // ...snip Interestingly, UDP/9 correlates to the canonical Discard Protocol, which is the TCP/UDP/IP equivalent of /dev/null. The CheckArpTables() function attempts to check the device ARP records, by calling the arp system command and greping the output. However, the user- controlled value passed as the LocalIPAddress is written directly into the command line format string with snprint(). This string is then passed directly to a function called FCGI_popen(), which is a library function imported from libfcgi.so. undefined CheckArpTables(char *LocalIPAddress, char *InternalPort, char *ProtocolType, undefined param_4, int param_5) { // ...snip... memset(buffer, 0, 0x40); // ...snip... snprintf(buffer, 0x40, "arp | grep %s | awk \'{printf $4}\'", LocalIPAddress); iVar1 = FCGI_popen(buffer, "r"); // ...snip... } We can see in libfcgi.so that FCGI_popen() is essentially only a thin wrapper around the stdio popen() library function. Arguments passed to FCGI_popen() get passed directly to popen(). int FCGI_popen(char *param_1, char *param_2) { FILE *__stream; int iVar1; __stream = popen(param_1,param_2); iVar1 = FCGI_OpenFromFILE(__stream); if ((__stream != (FILE *)0x0) && (iVar1 == 0)) { pclose(__stream); } return iVar1; } Since the LocalIPAddress value is not sanitized or checked in any way, a crafted command injection string can be passed as the LocalIPAddress, which will then be written to the arp command format string, and passed (almost) directly to popen(). ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Vulnerable / tested versions: ----------------------------- DIR-3060 v1.11b04 Solution: --------- Apply D-Link-supplied patch, v1.11b04 Hotfix 2. Advisory URL: ------------- https://www.iot-inspector.com/blog/advisory-d-link-dir-3060/ Vendor contact timeline: ------------------------ 2020-11-16: Initial contact made to ipsecure@dlinkcorp.com to request keys for encryption. 2020-11-20: No reply received, so follow-up e-mail sent. 2020-11-27: No reply received, so advisory sent by e-mail without encryption. 2021-02-03: No reply received, so follow-up e-mail sent. 2021-02-12: No reply received, so inquiry sent using the forms at support.dlink.com and eu.dlink.com/uk/en/contact-d-link. 2021-02-17: Response from the US D-Link support team, pointing us towards the US-specific D-Link security page. 2021-02-17: Sent e-mail to this new US-specific D-Link security e-mail address. 2021-02-19: Response from a member of the D-Link USA SIRT. 2021-02-19: We request a public key from D-Link USA for transmission of the advisory. 2021-02-19: PGP public key is provided by D-Link USA. 2021-02-19: Advisory is sent to D-Link USA with encryption. 2021-02-19: Receipt of advisory is confirmed by D-Link USA SIRT. 2021-02-19: We reply and ask for D-Link USA to keep us updated. 2021-02-20: D-Link ipsecure finally answers our e-mail, saying that security@dlink.com should be the official e-mail, and the ipsecure@dlinkcorp.com e-mail (the only one listed on the main D-Link security disclosure page) is only a backup address. 2021-02-22: D-Link USA responds, confirming that the e-mail address listed on the main D-Link security page has been changed. 2021-03-02: We e-mail D-Link USA to ask for a status update. 2021-03-02: D-Link USA responds with status update. 2021-03-08: D-Link USA provides patched firmware for testing. 2021-03-08: We respond asking for assigned CVE number. 2021-03-08: D-Link USA notes that they do not apply for, or manage CVE numbers related to their own products. 2021-03-08: We apply for a CVE number for this issue. 2021-03-08: D-Link USA publishes public advisory. 2021-03-11: CVE is assigned & IoT Inspector Research Lab publishes advisory. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The IoT Inspector Research Lab is an integrated part of IoT Inspector. IoT Inspector is a platform for automated security analysis and compliance checks of IoT firmware. Our mission is to secure the Internet of Things. In order to discover vulnerabilities and vulnerability patterns within IoT devices and to further enhance automated identification that allows for scalable detection within IoT Inspector, we conduct excessive security research in the area of IoT. Whenever the IoT Inspector Research Lab discovers vulnerabilities in IoT firmware, we aim to responsibly disclose relevant information to the vendor of the affected IoT device as well as the general public in a way that minimizes potential harm and encourages further security analyses of IoT systems. You can find our responsible disclosure policy here: https://www.iot-inspector.com/responsible-disclosure-policy/ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Interested in using IoT Inspector for your research or product? Mail: research at iot-inspector dot com Web: https://www.iot-inspector.com Blog: https://www.iot-inspector.com/blog/ Twitter: https://twitter.com/iotinspector EOF T Shiomitsu / @2021