Web Service: Dead Drop Resolver

Adversaries may use an existing, legitimate external Web service to host information that points to additional command and control (C2) infrastructure. Adversaries may post content, known as a dead drop resolver, on Web services with embedded (and often obfuscated/encoded) domains or IP addresses. Once infected, victims will reach out to and be redirected by these resolvers.

Popular websites and social media acting as a mechanism for C2 may give a significant amount of cover due to the likelihood that hosts within a network are already communicating with them prior to a compromise. Using common services, such as those offered by Google or Twitter, makes it easier for adversaries to hide in expected noise. Web service providers commonly use SSL/TLS encryption, giving adversaries an added level of protection.

Use of a dead drop resolver may also protect back-end C2 infrastructure from discovery through malware binary analysis while also enabling operational resiliency (since this infrastructure may be dynamically changed).

ID: T1102.001
Sub-technique of:  T1102
Tactic: Command And Control
Platforms: Linux, Windows, macOS
Permissions Required: User
Data Sources: Host network interface, Netflow/Enclave netflow, Network protocol analysis, Packet capture, SSL/TLS inspection
Version: 1.0
Created: 14 March 2020
Last Modified: 26 March 2020

Procedure Examples

Name Description
APT41

APT41 used legitimate websites for C2 through dead drop resolvers (DDR), including GitHub, Pastebin, and Microsoft TechNet.[15]

BADNEWS

BADNEWS collects C2 information via a dead drop resolver.[5][6][7]

BLACKCOFFEE

BLACKCOFFEE uses Microsoft’s TechNet Web portal to obtain a dead drop resolver containing an encoded tag with the IP address of a command and control server.[3][4]

BRONZE BUTLER

BRONZE BUTLER's MSGET downloader uses a dead drop resolver to access malicious payloads.[13]

MiniDuke

Some MiniDuke components use Twitter to initially obtain the address of a C2 server or as a backup if no hard-coded C2 server responds.[1][2]

Patchwork

Patchwork hides base64-encoded and encrypted C2 server locations in comments on legitimate websites.[14]

PlugX

PlugX uses Pastebin to store C2 addresses.[8]

Rocke

Rocke has used Pastebin to check the version of beaconing malware and redirect to another Pastebin hosting updated malware.[16]

RTM

RTM has used an RSS feed on Livejournal to update a list of encrypted C2 server names. RTM has also hidden Pony C2 server IP addresses within transactions on the Bitcoin and Namecoin blockchain.[10][11][12]

RTM

RTM has used an RSS feed on Livejournal to update a list of encrypted C2 server names.[10]

Xbash

Xbash can obtain a webpage hosted on Pastebin to update its C2 domain list.[9]

Mitigations

Mitigation Description
Network Intrusion Prevention

Network intrusion detection and prevention systems that use network signatures to identify traffic for specific adversary malware can be used to mitigate activity at the network level.

Restrict Web-Based Content

Web proxies can be used to enforce external network communication policy that prevents use of unauthorized external services.

Detection

Host data that can relate unknown or suspicious process activity using a network connection is important to supplement any existing indicators of compromise based on malware command and control signatures and infrastructure or the presence of strong encryption. Packet capture analysis will require SSL/TLS inspection if data is encrypted. User behavior monitoring may help to detect abnormal patterns of activity.[17]

References