legitimate tinycc usage by developers may trigger this detection if executed from non-standard locations. however, the combination of: 1. renamed binary (svchost.exe with tcc.exe originalfilename) 2. execution from user-writable directories (appdata, temp, programdata) 3. suspicious flags (-nostdlib -run) with .c file execution is highly suspicious and warrants investigation. legitimate tinycc usage typically occurs from program files or developer directories with standard compilation workflows. allowlist known development environments if needed.

splunk

Techniques

Sample rules

Windows TinyCC Shellcode Execution

source: splunk
technicques:

Description

Detects abuse of Tiny-C-Compiler (TinyCC) for shellcode execution, where tcc.exe is renamed to masquerade as svchost.exe and used to compile and execute C source files containing shellcode. This technique was observed in the Lotus Blossom Chrysalis backdoor campaign, where attackers renamed “tcc.exe” to “svchost.exe”, and executed a file named “conf.c” containing Metasploit block_api shellcode with the flags -nostdlib -run. TinyCC is a legitimate C compiler, but its ability to compile and execute code on-the-fly makes it attractive to attackers seeking to evade detection. The combination of a renamed compiler binary executing from non-standard locations with suspicious flags is a strong indicator of malicious activity.

Detection logic


| tstats `security_content_summariesonly`
  count min(_time) as firstTime
        max(_time) as lastTime

from datamodel=Endpoint.Processes where

Processes.process_name IN ("svchost.exe", "tcc.exe")
Processes.process="* -nostdlib*"
Processes.process="* -run*"
Processes.process IN ("*.c", "*conf.c*")
NOT Processes.process_path IN (
    "*:\\Windows\\System32\\*",
    "*:\\Windows\\SysWOW64\\*"
)

By Processes.action Processes.dest Processes.user Processes.process Processes.parent_process
   Processes.parent_process_exec Processes.parent_process_guid
   Processes.parent_process_id Processes.parent_process_name
   Processes.parent_process_path Processes.process_name Processes.process_id
   Processes.process_exec Processes.process_guid Processes.process_hash
   Processes.process_integrity_level Processes.process_path
   Processes.original_file_name Processes.user_id Processes.vendor_product


| `drop_dm_object_name(Processes)`

| `security_content_ctime(firstTime)`

| `security_content_ctime(lastTime)`

| `windows_tinycc_shellcode_execution_filter`