CVE-2021-27889

MEDIUM

MyBB < 1.8.26 - Cross-Site Scripting via Nested Auto URL Message Parsing

Title source: llm
STIX 2.1

Exploitation Summary

EIP tracks 1 public exploit for CVE-2021-27889.

AI-analyzed exploit summary This exploit chains a stored XSS vulnerability with a second-order SQL injection to achieve remote command execution in MyBB 1.8.25. It leverages improper string interpolation in PHP's eval() function to execute arbitrary commands via a reverse shell.

Description

Cross-site Scripting (XSS) vulnerability in MyBB before 1.8.26 via Nested Auto URL when parsing messages.

Exploits (1)

exploitdb WORKING POC
javascriptwebappsphp
https://www.exploit-db.com/exploits/49696

This exploit chains a stored XSS vulnerability with a second-order SQL injection to achieve remote command execution in MyBB 1.8.25. It leverages improper string interpolation in PHP's eval() function to execute arbitrary commands via a reverse shell.

Classification
Working Poc 95%
Attack Type
Rce
Complexity
Complex
Reliability
Reliable
Target: MyBB 1.8.25
Auth required
Prerequisites: Valid administrator ACP session · Ability to deliver malicious payload via MyCode (BBCode)
devstral-2 · analyzed Feb 19, 2026 Full analysis →

References (3)

Core 3
Core References
Patch, Third Party Advisory x_refsource_misc
https://github.com/mybb/mybb/security/advisories/GHSA-xhj7-3349-mqcm
Exploit, Third Party Advisory, VDB Entry x_refsource_misc
http://packetstormsecurity.com/files/161908/MyBB-1.8.25-Remote-Command-Execution.html
Exploit, Third Party Advisory x_refsource_misc
https://blog.sonarsource.com/mybb-remote-code-execution-chain

Scores

CVSS v3 6.1
EPSS 0.0096
EPSS Percentile 77.0%
Attack Vector NETWORK
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

Details

CWE
CWE-79
Status published
Products (1)
mybb/mybb < 1.8.26
Published Mar 15, 2021
Tracked Since Feb 18, 2026