critical CVSS 9.8

CVE-2021-4473·PHP vulnerability

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).

Severity
critical
Software
PHP
Fixed in
4.0.0.7_20210716.180815
Published
2026-04-07

Affected versions

Until: 4.0.0.7_20210716.180815

Fixed in: 4.0.0.7_20210716.180815

How to fix this CVE

Update the Tianxin Internet Behavior Management System firmware to version 4.0.0.7_20210716.180815 or later to patch the command injection vulnerability in the Reporter component. This vulnerability allows unauthenticated attackers to inject arbitrary shell commands through the objClass parameter, potentially leading to remote code execution. Immediately apply the available firmware update and verify the deployment across all affected systems.

sudo dnf update php

Defensia detects this vulnerability

What an exploitation attempt looks like

Sample log line indicative of exploitation attempts:

POST /reporter/toquery.php HTTP/1.1.*objClass=.*[;|`$()&<>].*

WAF mitigation (if patching is not yet possible)

Add this rule to your WAF to block exploitation attempts while you schedule the patch. 

Configure WAF rules to block POST requests to /reporter/toquery.php containing shell metacharacters (;, |, `, $(, &, <, >) in the objClass parameter; implement strict input validation requiring objClass values to match only alphanumeric characters and reject any requests with encoded variants of metacharacters.

How to check if you are affected

  1. Step 1: Verify your Tianxin system firmware version by accessing the web interface admin panel under System > Firmware Information and compare against 4.0.0.7_20210716.180815
  2. Step 2: Check if the Reporter component endpoint (/reporter/toquery.php or similar) is accessible without authentication by attempting an unauthenticated HTTP request to the web interface
  3. Step 3: Search web server access logs for requests containing 'objClass' parameter with shell metacharacters such as semicolons, pipes, backticks, or $() command substitution patterns
  4. Step 4: Inspect the web root directory and temporary locations for newly created PHP files with suspicious names or modification timestamps correlating with suspicious log entries

Indicators of compromise

  • HTTP POST requests to /reporter/toquery.php with objClass parameter containing semicolons or pipe characters
  • Newly created .php files in web root directories with timestamps matching suspicious HTTP request logs
  • Web server error logs showing command injection attempts with output redirection operators (>, >>)

FAQ

What is CVE-2021-4473?

CVE-2021-4473 is a critical command injection vulnerability in the Tianxin Internet Behavior Management System's Reporter component that enables unauthenticated attackers to execute arbitrary shell commands by crafting malicious objClass parameters, potentially resulting in unauthorized remote code execution.

Is CVE-2021-4473 being actively exploited?

According to CISA's Known Exploited Vulnerabilities (KEV) catalog, CVE-2021-4473 is not currently listed as actively exploited in the wild, though no public exploit has been officially released.

What versions of the Tianxin system are affected by CVE-2021-4473?

All firmware versions prior to 4.0.0.7_20210716.180815 are vulnerable; the vulnerability was patched in that specific firmware release and later versions.

How do I check if my Tianxin system is vulnerable to CVE-2021-4473?

Access your system's web administration interface, navigate to System > Firmware Information, and compare the displayed firmware version against 4.0.0.7_20210716.180815; versions earlier than this are vulnerable.

Does Defensia detect CVE-2021-4473?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If the Tianxin Internet Behavior Management System is deployed on a monitored server, CVE-2021-4473 will appear in your dashboard with remediation steps.

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References

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