CVE-2021-47888

HighPublic PoC

Published: 23 January 2026

Published

23 January 2026

Modified

15 April 2026

KEV Added

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Patch

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CVSS Score v4 8.7 CVSS:4.0/AV:N/AC:L/AT:N/PR:L/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 Score 0.0060 44.2th percentile

Risk Priority 55 floored blend · peak EPSS

Summary

CVE-2021-47888 is a high-severity Unrestricted Upload of File with Dangerous Type (CWE-434) vulnerability. Its CVSS base score is 8.7 (High).

Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked at the 44.2th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.

The strongest mitigations our analysis identified are NIST 800-53 SI-10 (Information Input Validation) and SI-2 (Flaw Remediation).

Deeper analysis

CVE-2021-47888 is an authenticated remote code execution vulnerability in Textpattern content management system versions prior to 4.8.3. It stems from CWE-434 (Unrestricted Upload of File with Dangerous Type), enabling logged-in users to upload malicious PHP files containing shell command execution payloads. By accessing the uploaded file via a specific URL parameter, attackers can trigger arbitrary command execution on the server.

The vulnerability requires network access and low privileges (PR:L), with no user interaction needed, as indicated by its CVSS v3.1 score of 8.8 (AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H). Any authenticated user, such as a contributor or low-level admin, can exploit it to gain full server compromise, including data exfiltration, persistence, or further lateral movement within the environment.

Mitigation involves upgrading to Textpattern 4.8.3 or later, as specified in the vulnerability details. Advisories from sources like VulnCheck and public exploits on Exploit-DB (e.g., 49620) highlight the issue, with Textpattern's official site providing relevant resources for patching.

A proof-of-concept exploit is publicly available on Exploit-DB, increasing the risk of real-world abuse against unpatched installations.

OWASP Top 10 for Web (2025)

EU & UK References

🇪🇺 ENISA EUVD: EUVD-2026-4283

Vulnerability details

Textpattern versions prior to 4.8.3 contain an authenticated remote code execution vulnerability that allows logged-in users to upload malicious PHP files. Attackers can upload a PHP file with a shell command execution payload and execute arbitrary commands by accessing the…

uploaded file through a specific URL parameter.

CWE(s): CWE-434

Related Threats

MITRE ATT&CK Enterprise TechniquesAI

T1190 Exploit Public-Facing Application Initial Access

Adversaries may attempt to exploit a weakness in an Internet-facing host or system to initially access a network.

attack.mitre.org →

T1505.003 Web Shell Persistence

Adversaries may backdoor web servers with web shells to establish persistent access to systems.

attack.mitre.org →

Why these techniques?

The vulnerability enables exploitation of a public-facing web application (T1190) via authenticated file upload of PHP web shells (T1100) for remote command execution.

Confidence: HIGH · MITRE ATT&CK Enterprise v19.0