// Concept of the malicious code injected into sysdeputil.c if ((str[i] == ':') && (str[i+1] == ')')) vsf_sysutil_extra(); Use code with caution. Port 6200 Binding
Ensure you are running a modern, supported version of VSFTPD downloaded from official package repositories (like apt or yum ) rather than unverified legacy source archives.
When those two characters were detected at the end of a username, the program executed vsf_sysutil_extra() . This function contained a hardcoded network socket routine that: Binds to TCP port 6200. vsftpd 208 exploit github link
Understanding and Exploiting the VSFTPD 2.3.4 Backdoor (CVE-2011-2523)
graph LR A[Attacker: Kali Linux] --> B[Network: Host‑Only] B --> C[Target: Metasploitable 2] C --> D[vsftpd 2.3.4 port 21] D --> E[Backdoor trigger: USER *:) ] E --> F[Root shell on port 6200] // Concept of the malicious code injected into sysdeputil
You should be dropped into an interactive root shell. You can now run any system command.
Ensure you are running a modern, supported version of vsftpd. Version 2.3.4 has been obsolete for over a decade. This function contained a hardcoded network socket routine
The compromised tarball was , and all modern Linux distributions have long since updated to patched versions (2.3.5 or later). However, the vulnerability remains a classic teaching tool in security courses and is preinstalled on purpose‑vulnerable virtual machines such as Metasploitable 2 .
is a legitimate, authorised profession. Many security professionals use vulnerable VMs like Metasploitable 2 to practise and refine their skills. However, performing an unauthorised test on a live server can lead to civil lawsuits, criminal charges, and termination of employment.
Attackers can therefore:
If the username ended with the characters :) (a smiley face), the backdoor triggered.
// Concept of the malicious code injected into sysdeputil.c if ((str[i] == ':') && (str[i+1] == ')')) vsf_sysutil_extra(); Use code with caution. Port 6200 Binding
Ensure you are running a modern, supported version of VSFTPD downloaded from official package repositories (like apt or yum ) rather than unverified legacy source archives.
When those two characters were detected at the end of a username, the program executed vsf_sysutil_extra() . This function contained a hardcoded network socket routine that: Binds to TCP port 6200.
Understanding and Exploiting the VSFTPD 2.3.4 Backdoor (CVE-2011-2523)
graph LR A[Attacker: Kali Linux] --> B[Network: Host‑Only] B --> C[Target: Metasploitable 2] C --> D[vsftpd 2.3.4 port 21] D --> E[Backdoor trigger: USER *:) ] E --> F[Root shell on port 6200]
You should be dropped into an interactive root shell. You can now run any system command.
Ensure you are running a modern, supported version of vsftpd. Version 2.3.4 has been obsolete for over a decade.
The compromised tarball was , and all modern Linux distributions have long since updated to patched versions (2.3.5 or later). However, the vulnerability remains a classic teaching tool in security courses and is preinstalled on purpose‑vulnerable virtual machines such as Metasploitable 2 .
is a legitimate, authorised profession. Many security professionals use vulnerable VMs like Metasploitable 2 to practise and refine their skills. However, performing an unauthorised test on a live server can lead to civil lawsuits, criminal charges, and termination of employment.
Attackers can therefore:
If the username ended with the characters :) (a smiley face), the backdoor triggered.