PHPMailer untrusted code may be run from an overridden address validatorGHSA-77mr-wc79-m8j3
HIGHFix: PHPMailer/PHPMailer@45f3c18GHSA-77mr-wc79-m8j3 is a high-severity (CVSS 8.1) CWE-829 vulnerability in phpmailer/phpmailer. A fix is available for phpmailer/phpmailer — see the affected versions and patch details below.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
GHSA-77mr-wc79-m8j3 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 395,492 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
Real-World Exposure
phpmailer/phpmailerReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Packagist packages — download data is not available via public APIs for these ecosystems.
Description
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 Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐘Packagist | phpmailer/phpmailer | all versions | 6.5.0composer require phpmailer/phpmailer:^6.5.0 |
Affected Products
fedorafedoraprojectphpmailerphpmailer_projectDetection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for phpmailer/phpmailer, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update phpmailer/phpmailer to 6.5.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-77mr-wc79-m8j3 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
Frequently Asked Questions
Is GHSA-77mr-wc79-m8j3 in your dependencies?
Find it across Packagist, including transitive dependencies.