{"id":"CVE-2021-27889","url":"https://www.cyber-defence.io/tools/cve/CVE-2021-27889","generatedAt":"2026-10-28T01:52:06.143Z","title":"Cross-site Scripting (XSS) vulnerability in MyBB before 1.8.26 via Nested Auto URL when parsing messages.","description":"Cross-site Scripting (XSS) vulnerability in MyBB before 1.8.26 via Nested Auto URL when parsing messages.","published":"2021-03-15T17:15:23.000Z","lastModified":"2026-06-17T03:45:34.000Z","status":"Modified","sourceIdentifier":"cve@mitre.org","cvss":{"version":"3.1","score":6.1,"severity":"MEDIUM","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N"},"cwe":["CWE-79"],"affected":["mybb/mybb"],"epss":{"score":0.05072,"percentile":0.92273,"date":"2026-10-26","history":[]},"kev":{"listed":false},"exploits":{"count":1,"verified":false,"firstPublished":"2021-03-22","source":"Exploit-DB (https://gitlab.com/exploit-database/exploitdb)","entries":[{"edbId":49696,"kind":"exploit","title":"MyBB 1.8.25 - Chained Remote Command Execution","url":"https://www.exploit-db.com/exploits/49696","sourceUrl":"https://gitlab.com/exploit-database/exploitdb/-/blob/main/exploits/php/webapps/49696.js","file":"exploits/php/webapps/49696.js","published":"2021-03-22","added":"2021-03-22","updated":"2021-03-23","author":"SivertPL","type":"webapps","platform":"php","port":null,"verified":false,"codes":["CVE-2021-27890","CVE-2021-27889"],"tags":null,"aliases":null,"applicationUrl":null,"screenshotUrl":null,"referenceUrl":null}]},"verdict":{"level":"high","text":"A public exploit is published in Exploit-DB, so the technical barrier is gone even though the severity is medium and EPSS is 5.1%. Treat it as high on anything reachable from the internet."},"changes":[],"references":[{"url":"http://packetstormsecurity.com/files/161908/MyBB-1.8.25-Remote-Command-Execution.html","tags":["Exploit","Third Party Advisory","VDB Entry"],"source":"cve@mitre.org"},{"url":"https://blog.sonarsource.com/mybb-remote-code-execution-chain","tags":["Exploit","Third Party Advisory"],"source":"cve@mitre.org"},{"url":"https://github.com/mybb/mybb/security/advisories/GHSA-xhj7-3349-mqcm","tags":["Patch","Third Party Advisory"],"source":"cve@mitre.org"},{"url":"http://packetstormsecurity.com/files/161908/MyBB-1.8.25-Remote-Command-Execution.html","tags":["Exploit","Third Party Advisory","VDB Entry"],"source":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"https://blog.sonarsource.com/mybb-remote-code-execution-chain","tags":["Exploit","Third Party Advisory"],"source":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"https://github.com/mybb/mybb/security/advisories/GHSA-xhj7-3349-mqcm","tags":["Patch","Third Party Advisory"],"source":"af854a3a-2127-422b-91ae-364da2661108"}],"sources":{"nvd":"https://nvd.nist.gov/vuln/detail/CVE-2021-27889","epss":"https://www.first.org/epss/","kev":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog","exploitdb":"https://www.exploit-db.com/"},"licence":"CC BY 4.0 — link back to the CVE Explorer if you publish the results; upstream data remains subject to its own terms."}