CVE-2016-10033: PHPMailer Command Injection Vulnerability

Should you act?

Exploited: patch now if you run it

CISA has confirmed exploitation in the wild. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• Yes, if you run PHP PHPMailer. CISA added this CVE to its Known Exploited Vulnerabilities catalog on 2025-07-07, which means there is reliable evidence of exploitation in the wild. US federal agencies must remediate by 2025-07-28; treat that as the outer limit, not the target.
• EPSS 99.7%, percentile 100.0: FIRST’s model estimates a 99.7% chance of exploitation activity in the next 30 days, higher than 100.0% of all scored CVEs (very high). EPSS is a probability, not a verdict.
• Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.

What it is

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.

CISA’s summary

PHPMailer contains a command injection vulnerability because it fails to sanitize user-supplied input. Specifically, this issue affects the 'mail()' function of 'class.phpmailer.php' script. An attacker can exploit this issue to execute arbitrary code within the context of the application. Failed exploit attempts will result in a denial-of-service condition.

Weakness type: CWE-88, CWE-77.

Product: PHP PHPMailer · Assigned by: mitre · Published: 2016-12-30

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Privileges required: none (no login)
• User interaction: none
• Scope: unchanged

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• CISA KEV: added 2025-07-07; federal due date 2025-07-28. Known ransomware use: Unknown.
• CISA required action: Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
• CISA SSVC assessment: exploitation active, automatable yes, technical impact total.
• FIRST EPSS (model of 2026-10-21): 99.71% probability of exploitation activity in the next 30 days; percentile 100.0.

Timeline

• 2016-12-30 — CVE record published by mitre
• 2025-07-07 — Added to CISA’s Known Exploited Vulnerabilities catalog
• 2025-07-28 — CISA remediation deadline for US federal agencies
• 2025-10-21 — CVE record last updated

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vendor and project advisories, patches

1. Listed in CISA KEV notes (github.com) github.com
2. Listed in CISA KEV notes (github.com) github.com

Vulnerability records

1. CVE.org record CVE-2016-10033 cve.org
2. NVD entry CVE-2016-10033 nvd.nist.gov

Government

1. CISA Known Exploited Vulnerabilities catalog entry cisa.gov

Other references from the CVE record and advisory

1. packetstormsecurity.com packetstormsecurity.com
2. drupal.org drupal.org
3. 42221 exploit-db.com
4. 40969 exploit-db.com
5. 41962 exploit-db.com
6. 40968 exploit-db.com
7. legalhackers.com legalhackers.com
8. 20161227 PHPMailer < 5.2.18 Remote Code Execution [updated advisory] [CVE-2016-10033] securityfocus.com
9. github.com github.com
10. packetstormsecurity.com packetstormsecurity.com
11. 40974 exploit-db.com
12. 40986 exploit-db.com
13. 40970 exploit-db.com
14. rapid7.com rapid7.com
15. 41996 exploit-db.com
16. 20161227 PHPMailer < 5.2.18 Remote Code Execution [CVE-2016-10033] seclists.org
17. 95108 securityfocus.com
18. 1037533 securitytracker.com
19. developer.joomla.org developer.joomla.org
20. 42024 exploit-db.com

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