What’s Vulnerable › Vulnerabilities

CVE-2021-27889

• Severity: medium (CVSS 6.1 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 5.1% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2021-03-15 · updated 2026-06-17
• Weakness: CWE-79

Description

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

Affected products

• mybb: before 1.8.26 — fixed in 1.8.26

How to fix

Upgrade to a fixed version: mybb 1.8.26. Check the vendor advisory for mitigations.

References

• http://packetstormsecurity.com/files/161908/MyBB-1.8.25-Remote-Command-Execution.html
• https://blog.sonarsource.com/mybb-remote-code-execution-chain
• https://github.com/mybb/mybb/security/advisories/GHSA-xhj7-3349-mqcm
• http://packetstormsecurity.com/files/161908/MyBB-1.8.25-Remote-Command-Execution.html
• https://blog.sonarsource.com/mybb-remote-code-execution-chain
• https://github.com/mybb/mybb/security/advisories/GHSA-xhj7-3349-mqcm

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