CVE-2016-10033
PHPMailer Command Injection Vulnerability
PHP PHPMailer
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.
Exploitation status
CISA Known Exploited Vulnerabilities
Listed by CISA on 7 July 2025. US federal agencies were required to remediate it by 28 July 2025.
EPSS — exploitation probability
FIRST puts the probability of exploitation activity in the next 30 days at 99.7%, which is higher than 99.9% of all scored vulnerabilities. EPSS is a forecast of activity, not a measure of severity, and it is rescored daily.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Frequently asked questions
Is CVE-2016-10033 being exploited by ransomware groups?
No ransomware group in this database is currently recorded as exploiting CVE-2016-10033.
What does CVE-2016-10033 affect?
CVE-2016-10033 affects PHP PHPMailer. 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.
How severe is CVE-2016-10033?
CVE-2016-10033 is rated CRITICAL with a CVSS base score of 9.8. EPSS puts the probability of exploitation in the next 30 days at 99.7%, higher than 99.9% of all scored vulnerabilities. It is listed in the CISA Known Exploited Vulnerabilities catalog, with a federal remediation deadline of 28 July 2025.
How should organisations respond to CVE-2016-10033?
Apply the vendor patch for PHP PHPMailer as the first priority, and treat any internet-facing instance as the most urgent. Because this vulnerability is associated with ransomware activity, also review whether the affected systems were reachable before patching, rather than assuming that patching alone closes the incident.