CVE-2016-10033

Remote code execution in PHPMailer

Workarounds

Filter and validate user input before passing it to internal functions.

References

https://nvd.nist.gov/vuln/detail/CVE-2016-10033
Related to a follow-on issue in https://nvd.nist.gov/vuln/detail/CVE-2016-10045

For more information

If you have any questions or comments about this advisory:

• Open a private issue in the PHPMailer project

The mailSend function in the default 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.

Untrusted input is inserted into a command that is later executed by the application, allowing the attacker to alter the intent of that command. Typical impact: arbitrary command execution in the application's environment.

CVE-2016-10033 has a CVSS score of 9.8 (Critical). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (5.2.18); upgrading removes the vulnerable code path.

Kodem intelligence

Already deployed Kodem?

Fixed in 5.2.18

1. What is CVE-2016-10033? CVE-2016-10033 is a critical-severity command injection vulnerability in phpmailer/phpmailer (composer), affecting versions >= 5.0.0, < 5.2.18. It is fixed in 5.2.18. Untrusted input is inserted into a command that is later executed by the application, allowing the attacker to alter the intent of that command.
2. How severe is CVE-2016-10033? CVE-2016-10033 has a CVSS score of 9.8 (Critical). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of phpmailer/phpmailer are affected by CVE-2016-10033? phpmailer/phpmailer (composer) versions >= 5.0.0, < 5.2.18 is affected.
4. Is there a fix for CVE-2016-10033? Yes. CVE-2016-10033 is fixed in 5.2.18. Upgrade to this version or later.
5. Is CVE-2016-10033 exploitable, and should I be worried? Whether CVE-2016-10033 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2016-10033 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2016-10033? Upgrade phpmailer/phpmailer to 5.2.18 or later.

Other vulnerabilities in phpmailer/phpmailer