Known exploited vulnerability
CVE-2016-10033
The short answer
CVE-2016-10033 affects n/a n/a and is rated critical (CVSS 9.8). CISA added it to the Known Exploited Vulnerabilities catalog on 2025-07-07: attackers are using it, so patch it first. Fixed versions are published for phpmailer/phpmailer (5.2.18).
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.
Weakness: CWE-88.
Severity
9.8 critical
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Exploited (CISA KEV)
Yes, since Jul 7, 2025
Federal due date Jul 28, 2025
EPSS, next 30 days
100%
Higher than 100% of scored CVEs
How it can be exploited
- Attack vector
- Network
- Attack complexity
- Low
- Privileges required
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality impact
- High
- Integrity impact
- High
- Availability impact
- High
What CISA says to do
Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
Affected packages and fixed versions
| Package | Ecosystem | Fixed in | Advisory |
|---|---|---|---|
| phpmailer/phpmailer | Packagist | 5.2.18 | GHSA-5f37-gxvh-23v6 |
Is it in your code? Drop your lockfile into the free vulnerability check, or let vulnerability watch check your repository every day and open the upgrade as a pull request.
Affected products
n/a. NVD's record lists the exact affected versions.
References
- developer.joomla.org/security-centre/668-20161205-phpmailer-security-advisory.html Third Party Advisory
- github.com/PHPMailer/PHPMailer/releases/tag/v5.2.18 PatchVendor Advisory
- github.com/PHPMailer/PHPMailer/wiki/About-the-CVE-2016-10033-and-CVE-2016-10045-vulnerabilities PatchVendor Advisory
- legalhackers.com/advisories/PHPMailer-Exploit-Remote-Code-Exec-CVE-2016-10033-Vuln.html ExploitPatchThird Party Advisory
- www.drupal.org/psa-2016-004 Third Party Advisory
- www.exploit-db.com/exploits/40968/ ExploitPatchThird Party AdvisoryVDB Entry
- www.exploit-db.com/exploits/40969/ ExploitThird Party AdvisoryVDB Entry
- www.exploit-db.com/exploits/40970/ ExploitPatchThird Party AdvisoryVDB Entry
- www.exploit-db.com/exploits/40974/ ExploitThird Party AdvisoryVDB Entry
- www.exploit-db.com/exploits/40986/ ExploitThird Party AdvisoryVDB Entry
- www.exploit-db.com/exploits/41962/ ExploitThird Party AdvisoryVDB Entry
- www.exploit-db.com/exploits/41996/ ExploitThird Party AdvisoryVDB Entry
Questions
Is CVE-2016-10033 being exploited?
Yes. CISA added CVE-2016-10033 to its Known Exploited Vulnerabilities catalog on 2025-07-07, with a federal remediation due date of 2025-07-28.
How do I fix CVE-2016-10033?
Upgrade to a fixed version: phpmailer/phpmailer (Packagist) 5.2.18. CISA's 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.
From NVD, CISA KEV, FIRST EPSS and OSV.dev, checked . Status on NVD: Analyzed. The description is NVD's text, quoted as published.
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