CVE-2016-10033
CRITICALCVE-2016-10033 is a critical-severity (CVSS 9.8) CWE-88 vulnerability in phpmailer/phpmailer. 37 public exploit references exist, so weaponization risk is real. 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
Exploitation Status
Actively exploited in the wild
- CISA’s SSVC triage classifies this CVE as under active exploitation.
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- A successful exploit gives an attacker total control of the affected component, not partial access.
Exploitation and automatability from CISA’s SSVC triage for CVE-2016-10033.
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.
How urgent is this, really
CVE-2016-10033 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE sits: patch-first territory.
Where this sits among everything scored
Of 371,625 CVEs with a current EPSS score, this one falls in the ≥ 90% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
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
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.
Vanilla Forums < 2.3 - Remote Code Execution
by Dawid Golunski · May 11, 2017
PHPMailer < 5.2.18 - Remote Code Execution
by anarc0der · Dec 29, 2016
PHPMailer < 5.2.20 with Exim MTA - Remote Code Execution
by phackt_ul · Jun 21, 2017
WordPress Plugin PHPMailer 4.6 - Host Header Command Injection (Metasploit)
by Metasploit · May 17, 2017
PHPMailer < 5.2.18 - Remote Code Execution
by Dawid Golunski · Dec 25, 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 26, 2016
PHPMailer < 5.2.20 - Remote Code Execution
by Dawid Golunski · Dec 27, 2016
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.
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 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.