CVE-2021-27889 json
Cross-site Scripting (XSS) vulnerability in MyBB before 1.8.26 via Nested Auto URL when parsing messages.
published 2021-03-15 5 y ago modified 2026-06-17 4 mo ago also EUVD-2021-14626
- cvss
- 6.1
- version 3.1, NVD
- cisa kev
- Not listed
- not in CISA's catalog
- epss
- 5.1%
- EPSS 5.1% chance of exploitation in 30 days, percentile 92%
- public exploits
- 1
- Exploit-DB
Summary
Cross-site Scripting (XSS) vulnerability in MyBB before 1.8.26 via Nested Auto URL when parsing messages.
Patch / fix
Timeline
- Published
- First public exploit (EDB-49696)
Exploit prediction
5.07% chance of exploitation in the next 30 days, higher than 92% of all scored CVEs (FIRST EPSS, 2026-11-08).
Exploits and checks
- EDB-49696 MyBB 1.8.25 - Chained Remote Command Execution webapps, 2021-03-22
- packetstormsecurity.com http://packetstormsecurity.com/files/161908/MyBB-1.8.25-Remote-Command-Execution.html referenced PoC, tagged "exploit" by a source, unverified
- blog.sonarsource.com https://blog.sonarsource.com/mybb-remote-code-execution-chain referenced PoC, tagged "exploit" by a source, unverified
CVSS scores
| assigned by | version | score | vector |
|---|---|---|---|
| NVD | 3.1 | 6.1 | CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N |
| NVD | 2.0 | 4.3 | AV:N/AC:M/Au:N/C:N/I:P/A:N |
Classification
- Weakness
-
- CWE-79 Improper Neutralization of Input During Web Page Generation
References
-
github.com
/mybb/mybb/security/advisories/GHSA-xhj7-3349-mqcm
patch, third-party-advisory
-
packetstormsecurity.com
/files/161908/MyBB-1.8.25-Remote-Command-Execution.html
exploit, third-party-advisory, vdb-entry
-
blog.sonarsource.com
/mybb-remote-code-execution-chain
exploit, third-party-advisory
Sources
- CVE List CVE-2021-27889
- NVD CVE-2021-27889
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