Remote code execution in PHPMailerGHSA-4pc3-96mx-wwc8
CRITICALGHSA-4pc3-96mx-wwc8 is a critical-severity (CVSS 9.8) CWE-77 vulnerability in phpmailer/phpmailer. 10 public exploit references exist, so weaponization risk is real. 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-4pc3-96mx-wwc8 by exploitation likelihood (EPSS) against impact (CVSS). In the shaded patch-first corner (EPSS 50%+, CVSS 7.0+).
Where this sits among everything scored
Of 395,249 CVEs with a current EPSS score, this one falls in the ≥ 90% 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
Impact
The isMail transport in PHPMailer before 5.2.20 might allow remote attackers to pass extra parameters to the mail command and consequently execute arbitrary code by leveraging improper interaction between the escapeshellarg function and internal escaping performed in the mail function in PHP. NOTE: this vulnerability exists because of an incorrect fix for CVE-2016-10033.
This issue really emphasises that it's worth avoiding the built-in PHP mail() function entirely.
Patches
Fixed in 5.2.20
Workarounds
Send via SMTP to localhost instead of calling the mail() function.
References
https://nvd.nist.gov/vuln/detail/CVE-2016-10045 See also https://nvd.nist.gov/vuln/detail/CVE-2016-10033
For more information
If you have any questions or comments about this advisory:
- Open a private issue in the PHPMailer project
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐘Packagist | phpmailer/phpmailer | ≥ 5.0.0&&< 5.2.20 | 5.2.20composer require phpmailer/phpmailer:^5.2.20 |
Affected Products
joomla\!joomlaphpmailerphpmailer_projectwordpresswordpressResearch use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
PHPMailer < 5.2.20 with Exim MTA - Remote Code Execution
by phackt_ul · Jun 21, 2017
PHPMailer < 5.2.20 - Remote Code Execution
by Dawid Golunski · Dec 27, 2016
PHPMailer < 5.2.20 / SwiftMailer < 5.4.5-DEV / Zend Framework / zend-mail < 2.4.11 - 'AIO' 'PwnScriptum' Remote Code Execution
by Dawid Golunski · Jan 2, 2017
Detection & 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 5.2.20 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-4pc3-96mx-wwc8 is resolved across your whole dependency graph.
Workarounds
Stop passing untrusted input into the interpreter or shell: call the affected binary with an argument array rather than a composed command string, reject anything outside a strict allowlist of expected values, and run the component under an account that cannot reach beyond the work it legitimately does.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
Frequently Asked Questions
Is GHSA-4pc3-96mx-wwc8 in your dependencies?
Find it across Packagist, including transitive dependencies.