CVE-2024-3721: TBK DVR RCE Vulnerability via Command Injection

CVE-2024-3721 Overview

CVE-2024-3721 is an operating system command injection vulnerability affecting TBK DVR-4104 and DVR-4216 digital video recorders through firmware version 20240412. The flaw resides in the handling of the /device.rsp endpoint when invoked with opt=sys&cmd=___S_O_S_T_R_E_A_MAX___. Attackers manipulate the mdb and mdc request parameters to inject arbitrary shell commands. The issue is classified under CWE-78 and was assigned the identifier VDB-260573. A public proof-of-concept exists in the netsecfish GitHub repository.

Critical Impact
Remote authenticated attackers can execute arbitrary operating system commands on affected DVR appliances, enabling device takeover and pivoting into surveillance networks.

Affected Products

TBK DVR-4104 (firmware versions up to 20240412)
TBK DVR-4216 (firmware versions up to 20240412)
Rebranded OEM DVR variants sharing the same firmware base

Discovery Timeline

2024-04-13 - CVE-2024-3721 published to NVD with public disclosure of the exploit
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2024-3721

Vulnerability Analysis

The vulnerability exists in the web management interface exposed by affected TBK DVR devices. The /device.rsp handler accepts a special command token ___S_O_S_T_R_E_A_MAX___ under opt=sys. Within that code path, the handler reads the mdb and mdc HTTP parameters and passes their values into a shell command constructor without sanitization or safe-argument APIs. An attacker sends a crafted HTTP GET request over the network to trigger command execution as the DVR service account, which typically runs with root privileges on embedded Linux firmware.

The high EPSS probability score reflects active scanning and exploitation attempts against internet-exposed devices. Shodan and Censys queries commonly reveal thousands of TBK-branded DVRs exposed on TCP/80 and TCP/8080.

Root Cause

The root cause is improper neutralization of special elements used in an OS command [CWE-78]. The firmware concatenates attacker-controlled parameter values directly into a command string that is executed by a shell interpreter. Shell metacharacters such as ;, |, &&, and backticks are passed through unchanged, allowing arbitrary command chaining.

Attack Vector

Exploitation is remote and does not require user interaction. An attacker issues an HTTP request to the DVR web interface targeting the vulnerable endpoint with shell metacharacters embedded in the mdb or mdc argument. Successful exploitation returns command output through the response or enables blind execution such as reverse shells, cryptomining payload deployment, and botnet enlistment. Public reporting associates this vulnerability with recruitment into Mirai-class botnets.

A representative malicious request targets /device.rsp?opt=sys&cmd=___S_O_S_T_R_E_A_MAX___&mdb=<injected-command>&mdc=<injected-command> where the injected values contain shell separators followed by attacker commands. Refer to the public proof-of-concept for the exact request structure.

Detection Methods for CVE-2024-3721

Indicators of Compromise

Inbound HTTP requests to /device.rsp containing the token ___S_O_S_T_R_E_A_MAX___
Requests where mdb or mdc parameters contain shell metacharacters such as ;, |, `, $(, or URL-encoded equivalents %3B, %7C
Outbound connections from DVR management IP ranges to unknown command-and-control hosts on non-standard ports
Unexpected wget, curl, tftp, or busybox invocations sourced from DVR devices

Detection Strategies

Deploy network intrusion detection signatures that match HTTP requests containing the ___S_O_S_T_R_E_A_MAX___ marker combined with metacharacters in query parameters
Ingest firewall and web proxy logs into a SIEM and alert on requests to /device.rsp originating from external IP space
Baseline outbound connectivity from surveillance VLANs and alert on new destinations or ports

Monitoring Recommendations

Monitor perimeter logs for HTTP traffic destined to DVR management ports (typically TCP/80, TCP/8080, TCP/8000)
Correlate scan traffic with public exploit patterns published in the netsecfish PoC repository
Track threat intelligence feeds for TBK DVR botnet indicators and update block lists accordingly

How to Mitigate CVE-2024-3721

Immediate Actions Required

Remove affected DVR devices from direct internet exposure and place them behind a VPN or firewall access control list
Restrict management interface access to a dedicated administrative subnet using source IP allowlists
Change default and shared credentials on all TBK DVR appliances to reduce authenticated attack paths
Audit devices for signs of compromise including unauthorized processes, cron jobs, or modified startup scripts

Patch Information

No official vendor patch is referenced in the NVD entry for CVE-2024-3721 at the time of publication. Operators should contact TBK Vision or the original equipment manufacturer for firmware updates. Where no patch is available, treat affected devices as end-of-life and plan replacement with supported hardware.

Workarounds

Block external access to TCP/80, TCP/8080, and any custom DVR management ports at the perimeter firewall
Segment surveillance devices onto an isolated VLAN with egress filtering that permits only required destinations
Deploy a reverse proxy or web application firewall rule that drops requests containing the ___S_O_S_T_R_E_A_MAX___ token
Disable remote management features and rely on local console administration where feasible

bash

# Example iptables rule to block external access to the DVR management port
iptables -A INPUT -p tcp --dport 80 -s 0.0.0.0/0 -j DROP
iptables -A INPUT -p tcp --dport 80 -s 10.10.20.0/24 -j ACCEPT

# Example WAF rule fragment (ModSecurity) to block exploit token
SecRule REQUEST_URI "@contains ___S_O_S_T_R_E_A_MAX___" \
    "id:1002024,phase:1,deny,status:403,msg:'CVE-2024-3721 exploit attempt'"