PHPMailer untrusted code may be run from an overridden address validator
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().
Impact
Low impact – exploitation requires that an attacker can already inject code into an application, but it provides a trigger pathway.
Patches
This 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.
Workarounds
Inject your own email validator function.
References
Reported by Vikrant Singh Chauhan via huntr.dev. CVE-2021-3603
For more information
If you have any questions or comments about this advisory:
- Open an issue in the PHPMailer project
- Email us.
Affected software
Click a technology to see all vulnerabilities affecting it.
| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Composer package | phpmailer/phpmailer | < 6.5.0 | 6.5.0 |
References
- https://github.com/PHPMailer/PHPMailer/security/advisories/GHSA-77mr-wc79-m8j3
- https://nvd.nist.gov/vuln/detail/CVE-2021-3603
- https://github.com/PHPMailer/PHPMailer/commit/45f3c18dc6a2de1cb1bf49b9b249a9ee36a5f7f3
- https://github.com/FriendsOfPHP/security-advisories/blob/master/phpmailer/phpmailer/CVE-2021-3603.yaml
- https://github.com/PHPMailer/PHPMailer
- https://github.com/PHPMailer/PHPMailer/releases/tag/v6.5.0
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/3YRMWGA4VTMXFB22KICMB7YMFZNFV3EJ
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/FJYSOFCUBS67J3TKR74SD3C454N7VTYM
- https://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2021-3603
- https://www.huntr.dev/bounties/1-PHPMailer/PHPMailer
- CVSS vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H- Weakness (CWE)
CWE-74, CWE-829- Platform
- Composer
- Package
phpmailer/phpmailer- Disclosed
- 22.06.2021
- Updated
- 11.10.2026 10:22
Sources and licenses
OSV / GitHub Advisory Database - GHSA-77mr-wc79-m8j3 - CC BY 4.0
Vulnerability history: phpmailer/phpmailer
All published vulnerabilities of this package (Composer package), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 13
- First → latest
- 12.2016 02.2024
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- Critical 2
- High 7
- Medium 3
- Low 1
Disclosures per year
- 2017: 0
- 2018: 0
- 2019: 0
- 2020: 5
- 2021: 3
- 2022: 2
- 2023: 0
- 2024: 2
- 2025: 0
- 2026: 0
earlier: 1
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PHPMailer untrusted code may be run from an overridden address validator this entry
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