Cross-site scripting in MyBB - CVE-2021-27889
Published: March 17, 2021 / Updated: April 7, 2022
Vulnerability identifier: #VU51535
CSH Severity: Low
CVSS v4: 5.1 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N]
CVE-ID: CVE-2021-27889
CWE-ID: CWE-79
Exploitation vector: Remote access
Exploit availability:
Public exploit is available
Vulnerability details
The disclosed vulnerability allows a remote attacker to perform cross-site scripting (XSS) attacks.
The vulnerability exists due to insufficient sanitization of user-supplied data within the Nested Auto URL when parsing messages. A remote attacker can trick the victim to follow a specially crafted link and execute arbitrary HTML and script code in user's browser in context of vulnerable website.
Successful exploitation of this vulnerability may allow a remote attacker to steal potentially sensitive information, change appearance of the web page, perform phishing and drive-by-download attacks.
Affected software
MyBB
How to mitigate CVE-2021-27889
Install update from vendor's website.
MyBB - update to 1.8.26
Links to Public Exploits and PoC-codes
- Exploit #7616 - Mybb-XSS_SQL_RCE-POC (Mybb associate CVE-2021-27890 & CVE-2021-27889 to RCE poc) (April 7, 2022)
- Exploit #5595 - MyBB 1.8.25 - Poll Vote Count SQL Injection (June 17, 2021)
- Exploit #5598 - MyBB 1.8.25 - Chained Remote Command Execution (June 17, 2021)
- Exploit #5240 - MyBB 1.8.25 Remote Command Execution (March 24, 2021)