Recently, in the process of analyzing network attack logs based on threat intelligence, Alibaba Cloud's Security Team discovered an attack using the vulnerability of ShowDoc to spread botnets and mining software. This botnet spreading event has not yet been publicly reported.
ShowDoc is an online document sharing tool that provides developers with document writing and team collaboration features based on APIs. As early as August 2020, a vulnerability of arbitrary file upload was exposed and was numbered CNVD-2020-49480. The specific cause of this vulnerability is that when the file upload interface is called, the suffix logic of the verification file is incorrect, and the upload interface lacks permission authentication.
As a result, attackers can bypass authentication and suffix detection to upload webshell directly. Based on this, they can implant malicious programs relating to DDoS attacks and mining to execute arbitrary files.
Figure 1: Patch for vulnerability fixing
When implementing the file upload interface, ShowDoc refers to the code implementation logic from the older version. The whitelist array of attachment suffixes is restricted by the
$upload->allowExts parameter in Think PHP 3.1. In fact, after Think PHP 3.2, this logic is modified. The new one is implemented by using
$upload->exts, resulting in no whitelist restriction on suffixes. The php file upload check is bypassed, and webshell files can be uploaded directly. The principle of using this vulnerability is relatively simple. The PoC attack code has already been published on the Internet. Attackers can easily integrate it into the attack library.
Although ShowDoc released a patch for this vulnerability in August last year, it is found on the Internet that a small number of ShowDoc services have not been upgraded to the latest version. These websites of earlier versions are vulnerable to intrusion after being scanned and identified by attackers. They are prone to suffer continuous attacks and implantation of malicious programs, causing continuous interception alerts about malicious behaviors from Security Center.
Figure 2: Attack process
This wave of attacks was first detected on April 24. Through the attack logs, it is assumed that the attacker has developed a scanning tool to identify ShowDoc assets. The attacker uses Python to automatically exploit the vulnerability to upload webshell, record webshell paths, and further install malicious codes relating to DDoS attacks and mining on the basis of webshell.
The main implanted malwares include DDoS Trojan and Monero mining software, involving malwares from the Srv-Hello, Mirai, BillGates, and other families. The related malware families have been reported and analyzed many times, so this article will not analyze them again.
Figure 3: Query result on threat intelligence
By querying Alibaba Cloud threat intelligence, we can further obtain historical attack information and related data. For example, by querying the IP address
194[.]145.227.21, we found that this IP address not only provides downloads of malicious attack load but also actively scans a variety of common web systems and services. It exploits various vulnerabilities to initiate external attacks to spread malicious code and is in an active state.
Although ShowDoc is not a common web program, it is still noticed by attackers as an attack target. This shows that attackers actively integrate various vulnerabilities driven by interests. As long as the program has vulnerabilities, these vulnerabilities will be quickly integrated into the library and used to automatically spread malicious code.
This also poses new challenges to security practitioners and requires continuous monitoring to discover new attack methods. By combining with threat intelligence, these potential new attack methods can be discovered, and attacks can be handled more efficiently.
Public/Uploads/2021-XX-XX/, and delete the webshell.
hxxp://126.96.36.199:999/BOT/1 hxxp://188.8.131.52:85/Content/Upload/Activity/20210725043923.jpg hxxp://184.108.40.206:1234/xmss hxxp://220.127.116.11:802/25000 hxxp://18.104.22.168:802/LinuxTF hxxp://22.214.171.124:802/Manager hxxp://126.96.36.199:802/linuxdoor hxxp://188.8.131.52:802/manager hxxp://184.108.40.206:881/25 hxxp://220.127.116.11:881/BOT hxxp://18.104.22.168:881/L26 hxxp://22.214.171.124:991/25000 hxxp://126.96.36.199:8001/hackable/uploads/13.sh hxxp://188.8.131.52:8001/hackable/uploads/unixt hxxp://184.108.40.206:9876/ddos32-64 hxxp://220.127.116.11:8080/Q hxxp://18.104.22.168:8080/c hxxp://22.214.171.124:8080/door hxxp://126.96.36.199:8080/12.4 hxxp://188.8.131.52:8080/13 hxxp://184.108.40.206:8080/Manager hxxp://220.127.116.11:8080/linuxdoor hxxp://18.104.22.168:8080/vv hxxp://22.214.171.124:8080/ww hxxp://126.96.36.199:8080/32u hxxp://188.8.131.52:8080/dos32 hxxp://184.108.40.206/ldr.sh?b54287f2 hxxp://220.127.116.11/ldr.sh?localssh hxxp://18.104.22.168/sys.x86_64 hxxp://22.214.171.124/s.cmd hxxp://1w.kacdn.cn:81/Linux-syn10000 hxxp://126.96.36.199/1 hxxp://188.8.131.52/132 hxxp://184.108.40.206/udp hxxp://220.127.116.11:8080/syn
1[.]117.4.172 104[.[244.73.78 107[.]172.214.23 107[.]189.7.37 117[.]24.13.169 119[.]45.253.226 168[.]206.255.6 180[.]215.192.107 180[.]215.192.123 180[.]215.194.46 180[.]215.194.46 194[.]145.227.21 194[.]56.226.37 1w.kacdn.cn 209[.]141.34.100 216[.]83.33.79
e196d8c69ea072edd4313a0a9265b386 f6ba14ab7e8f5513cc81035e13615dec b7d56da2a700d17f27cfb504012cc6c7 57c5af8338ff8bd9abfe878ba9e8e661 346fe44a4d58863a098b72e1584e95e8 d51ba1fee712aac5a3a17129782115af d4989e13b700431c8760013a990edf0d da63a2f797b27f31745cfb8f94479bf4 d51ba1fee712aac5a3a17129782115af c67607c0927154a4d2efd79ad502cc7d 46c7302fe138e6a877755a3b5203303a 346fe44a4d58863a098b72e1584e95e8 da63a2f797b27f31745cfb8f94479bf4 a419dfe06954bc6bfbe7115d0ae95102 c9ab5b3125119fd83ffb0b27b392d613 7c50cd6c767052e28a23c4d89c90983a a158814f8a22c68987be16e79c8bff0f e611eafc4b5e422a2665bf5644b818e3 1d228318d5f2fefe4b04f82449777e40 122e36483aa697f8d6df252b76c1c8bf 06f25d5598cb026c0b97484ad80a3b43 542b52ae8f4d6dde9eb2fdc003eedc42 e5c3720e14a5ea7f678e0a9835d28283 229e3933010d9c32dff880658dc4119e 3997fb6cd3b603aad1cd40360be6c205 a0d22042fe2c365d7b07a04b2b1e1da0 0f649adcf96f6cac038ec7999d5aeffe 58d23f22bae9043697d8550ea0bc9b66 ed27862f885c906e30227d203b0084e2 0abd9797cd648a1d489fef86f0370387 afba98469d91f7fda00027870bfad553 16d4b49cd81775097ea2e997a90a2f4e
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