Is there a public PoC exploit available for CVE-2021-4473?

Yes, a public proof-of-concept exploit is available for CVE-2021-4473. Prioritise patching immediately. EPSS: 0.6%.

Is there a patch available for CVE-2021-4473?

Yes, a patch is available for CVE-2021-4473. Update the affected software to the latest version immediately.

PHP CVE-2021-4473

Q: What is the CVSS score of CVE-2021-4473?

CVE-2021-4473 has a CVSS 4.0 base score of 9.3 (Critical). CVSS vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X. EPSS exploitation probability: 0.6%.

EUVD-2021-34776 CRITICAL

OS Command Injection (CWE-78)

2026-04-07 VulnCheck

RCE PHP Command Injection

9.3

CVSS 4.0 · NVD

Severity by source

NVD PRIMARY

9.3 CRITICAL

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Primary rating from NVD · only source for this CVE.

CVSS VectorNVD

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Lifecycle Timeline

PoC Detected

Apr 07, 2026 - 13:20 vuln.today

Public exploit code

EUVD ID Assigned

Apr 07, 2026 - 13:00 euvd

EUVD-2021-34776

Patch released

Apr 07, 2026 - 13:00 nvd

Patch available

CVE Published

Apr 07, 2026 - 12:50 nvd

CRITICAL 9.3

DescriptionCVE.org

Tianxin Internet Behavior Management System contains a command injection vulnerability in the Reporter component endpoint that allows unauthenticated attackers to execute arbitrary commands by supplying a crafted objClass parameter containing shell metacharacters and output redirection. Attackers can exploit this vulnerability to write malicious PHP files into the web root and achieve remote code execution with the privileges of the web server process. This vulnerability has been fixed in version NACFirmware_4.0.0.7_20210716.180815_topsec_0_basic.bin. Exploitation evidence was first observed by the Shadowserver Foundation on 2024-06-01 (UTC).

AnalysisAI

Tianxin Internet Behavior Management System contains a command injection vulnerability in the Reporter component endpoint that allows unauthenticated attackers to execute arbitrary commands by. Rated critical severity (CVSS 9.3), this vulnerability is remotely exploitable, no authentication required, low attack complexity. Public exploit code available.

Technical ContextAI

This vulnerability is classified as OS Command Injection (CWE-78), which allows attackers to execute arbitrary operating system commands on the host. Tianxin Internet Behavior Management System contains a command injection vulnerability in the Reporter component endpoint that allows unauthenticated attackers to execute arbitrary commands by supplying a crafted objClass parameter containing shell metacharacters and output redirection. Attackers can exploit this vulnerability to write malicious PHP files into the web root and achieve remote code execution with the privileges of the web server process. This vulnerability has been fixed in version NACFirmware_4.0.0.7_20210716.180815_topsec_0_basic.bin. Exploitation evidence was first observed by the Shadowserver Foundation on 2024-06-01 (UTC). Affected products include: Beijing Topsec Network Security Technology Co., Ltd. Tianxin Internet Behavior Management System.

RemediationAI

A vendor patch is available. Apply the latest security update as soon as possible. Avoid passing user input to shell commands. Use language-specific APIs instead of shell execution. Apply strict input validation with allowlists.