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CVE-2016-10033: PHPMailer Command Injection Vulnerability

CVE-2016-10033 is rated critical with a CVSS v3.1 base score of 9.8 and affects PHP PHPMailer, along with 2 other products in NVD’s configuration data. Per its scoring, it can be exploited over the network, without authentication, without any user interaction. The scored impact on confidentiality, integrity and availability is the highest available. CISA added it to its Known Exploited Vulnerabilities catalog on 2025-07-07, which means exploitation in the wild has been observed.

Vulnerability 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.

Severity breakdown

CVSS v3.1 9.8: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

• Attack vector: Network. Exploitable remotely over the network, with no need for local or physical access.
• Attack complexity: Low. No special conditions; the attack can be repeated reliably.
• Privileges required: None. No account or prior access is needed.
• User interaction: None. No action from any user is needed.
• Scope: Unchanged. Impact stays within the vulnerable component.
• Confidentiality impact: High. Total loss of confidentiality; sensitive data can be fully disclosed.
• Integrity impact: High. Total loss of integrity; data or system state can be fully modified.
• Availability impact: High. Total loss of availability; the component can be shut down.

Underlying weakness

CWE-88: Improper Neutralization of Argument Delimiters in a Command

The product constructs a string for a command to be executed by a separate component in another control sphere, but it does not properly delimit the intended arguments, options, or switches within that command string.

Affected products

• Phpmailer Project: before 5.2.18
• WordPress: up to and including 4.7
• Joomla!: from 1.5.0 up to and including 3.6.5

References

• http://seclists.org/fulldisclosure/2016/Dec/78
• https://github.com/PHPMailer/PHPMailer/releases/tag/v5.2.18
• https://github.com/PHPMailer/PHPMailer/wiki/About-the-CVE-2016-10033-and-CVE-2016-10045-vulnerabilities
• https://legalhackers.com/advisories/PHPMailer-Exploit-Remote-Code-Exec-CVE-2016-10033-Vuln.html
• https://www.exploit-db.com/exploits/40968/
• https://www.exploit-db.com/exploits/40970/
• http://packetstormsecurity.com/files/140291/PHPMailer-Remote-Code-Execution.html
• http://packetstormsecurity.com/files/140350/PHPMailer-Sendmail-Argument-Injection.html
• http://www.rapid7.com/db/modules/exploit/multi/http/phpmailer_arg_injection
• http://www.securityfocus.com/archive/1/539963/100/0/threaded
• http://www.securityfocus.com/bid/95108
• http://www.securitytracker.com/id/1037533
• https://developer.joomla.org/security-centre/668-20161205-phpmailer-security-advisory.html
• https://www.drupal.org/psa-2016-004