CVE-2016-10033
CRITICALCVE-2016-10033 is a critical-severity (CVSS 9.8) CWE-88 vulnerability in phpmailer/phpmailer. It is in CISA's Known Exploited Vulnerabilities catalog (added 2025-07-07) — treat it as actively exploited and patch now. O3 Security confirms whether CVE-2016-10033 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Remote code execution in PHPMailer
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
Blast Radius
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
The mailSend function in the isMail transport in PHPMailer before 5.2.18 might allow remote attackers to pass extra parameters to the mail command and consequently execute arbitrary code via a " (backslash double quote) in a crafted Sender property.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐘Packagist | phpmailer/phpmailer | ≥ 5.0.0&&< 5.2.18 | 5.2.18 |
Research 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 < 5.2.18 - Remote Code Execution
by anarc0der · Dec 29, 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
WordPress Core 4.6 - Remote Code Execution
by Dawid Golunski · May 3, 2017
PHPMailer < 5.2.18 - Remote Code Execution
by Dawid Golunski · Dec 25, 2016
PHPMailer < 5.2.20 - Remote Code Execution
by Dawid Golunski · Dec 27, 2016
Vanilla Forums < 2.3 - Remote Code Execution
by Dawid Golunski · May 11, 2017
PHPMailer < 5.2.18 - Remote Code Execution
by Dawid Golunski · Dec 26, 2016
WordPress Plugin PHPMailer 4.6 - Host Header Command Injection (Metasploit)
by Metasploit · May 17, 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. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update phpmailer/phpmailer to 5.2.18 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2016-10033 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.
How O3 protects you
O3 pinpoints whether CVE-2016-10033 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to CVE-2016-10033. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2016-10033 in your dependencies?
O3 detects CVE-2016-10033 across Packagist dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.