{"id":"CVE-2021-3603","aliases":["BIT-phpmailer-2021-3603","GHSA-77mr-wc79-m8j3"],"url":"https://o3.security/vulnerability/CVE-2021-3603","summary":"PHPMailer untrusted code may be run from an overridden address validator","details":"If a function is defined that has the same name as the default built-in email address validation scheme (`php`), it will be called in default configuration as when no validation scheme is provided, the default scheme's callable `php` was being called. If an attacker is able to inject such a function into the application (a much bigger issue), it will be called whenever an email address is validated, such as when calling `validateAddress()`.\n\n### Impact\nLow impact – exploitation requires that an attacker can already inject code into an application, but it provides a trigger pathway.\n\n### Patches\nThis is patched in PHPMailer 6.5.0 by denying the use of simple strings as validator function names, which is a very minor BC break.\n\n### Workarounds\nInject your own email validator function.\n\n### References\nReported by [Vikrant Singh Chauhan](mailto:vi@hackberry.xyz) via [huntr.dev](https://www.huntr.dev/).\n[CVE-2021-3603](https://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2021-3603)\n\n### For more information\nIf you have any questions or comments about this advisory:\n* Open an issue in [the PHPMailer project](https://github.com/PHPMailer/PHPMailer)\n* [Email us](mailto:phpmailer@synchromedia.co.uk).\n","published":"2021-06-17T12:15:08.150Z","modified":"2026-10-20T10:54:47.063810576Z","cvss":{"score":8.1,"severity":"HIGH","vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H"},"epss":{"score":0.0226,"percentile":0.81482,"asOf":"2026-08-23"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"Packagist","name":"phpmailer/phpmailer","fixedVersion":"6.5.0"}],"fix":{"url":"https://github.com/PHPMailer/PHPMailer/commit/45f3c18dc6a2de1cb1bf49b9b249a9ee36a5f7f3","label":"PHPMailer/PHPMailer@45f3c18"},"references":[{"type":"WEB","url":"https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/3YRMWGA4VTMXFB22KICMB7YMFZNFV3EJ/"},{"type":"WEB","url":"https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/FJYSOFCUBS67J3TKR74SD3C454N7VTYM/"},{"type":"WEB","url":"https://www.huntr.dev/bounties/1-PHPMailer/PHPMailer/"},{"type":"FIX","url":"https://github.com/PHPMailer/PHPMailer/commit/45f3c18dc6a2de1cb1bf49b9b249a9ee36a5f7f3"},{"type":"WEB","url":"https://github.com/PHPMailer/PHPMailer/security/advisories/GHSA-77mr-wc79-m8j3"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2021-3603"},{"type":"WEB","url":"https://github.com/FriendsOfPHP/security-advisories/blob/master/phpmailer/phpmailer/CVE-2021-3603.yaml"},{"type":"PACKAGE","url":"https://github.com/PHPMailer/PHPMailer"},{"type":"WEB","url":"https://github.com/PHPMailer/PHPMailer/releases/tag/v6.5.0"},{"type":"WEB","url":"https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/3YRMWGA4VTMXFB22KICMB7YMFZNFV3EJ"},{"type":"WEB","url":"https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/FJYSOFCUBS67J3TKR74SD3C454N7VTYM"},{"type":"WEB","url":"https://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2021-3603"},{"type":"WEB","url":"https://www.huntr.dev/bounties/1-PHPMailer/PHPMailer"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-10-20T10:54:47.063810576Z"}}