How severe is CVE-2016-10033?

CVE-2016-10033 has a CVSS score of 9.8/10, rated CRITICAL. Immediate patching is strongly recommended.

Which packages are affected by CVE-2016-10033?

CVE-2016-10033 affects the following packages: phpmailer/phpmailer (Packagist). Ecosystems affected: Packagist.

How do I fix CVE-2016-10033?

Update phpmailer/phpmailer to version 5.2.18 or later. Run your dependency manager's update command and verify no transitive dependencies pin the vulnerable version. Use O3 Security's SCA scanner to confirm the fix is applied across your entire dependency tree.

Is CVE-2016-10033 actively exploited in the wild?

Yes. There are 37 known exploit references for CVE-2016-10033, including 9 documented proof-of-concept exploits on Exploit-DB and 23 in-the-wild exploitations observed on GitHub and other sources. Treat this as actively exploitable and prioritize patching immediately. All exploit code should only be run in an isolated sandbox environment for research or authorized testing — never against production systems without explicit written authorization.

What is the EPSS score for CVE-2016-10033?

CVE-2016-10033 has an EPSS (Exploit Prediction Scoring System) score of 94.4%, placing it in the 100th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. A score above 50% indicates significantly elevated exploitation risk — immediate patching is strongly recommended.

Is CVE-2016-10033 in the CISA Known Exploited Vulnerabilities catalog?

Yes. CVE-2016-10033 (PHPMailer Command Injection Vulnerability) was added to CISA's Known Exploited Vulnerabilities (KEV) catalog on 2025-07-07. CISA required all US federal civilian agencies to remediate this vulnerability by 2025-07-28. The required action was: Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable. Being listed in the KEV catalog is the strongest possible confirmation of active exploitation — treat this as a critical priority.

What type of vulnerability is CVE-2016-10033?

CVE-2016-10033 is classified as CWE-88 (CWE-88). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

Is there exploit tooling available for CVE-2016-10033?

A Nuclei detection template exists for CVE-2016-10033, meaning automated scanners can fingerprint it. Public exploit tooling significantly increases real-world risk — prioritize patching and ensure detection coverage. Exploit tooling should only ever be used in isolated, authorized testing environments.

When was CVE-2016-10033 published, and has it been updated?

CVE-2016-10033 was published on December 30, 2016 and was last updated on April 16, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

CISA KEV·Added 2025-07-07 — agencies required to remediate by 2025-07-28

🐘 Packagist

CVE-2016-10033

CRITICAL

Remote code execution in PHPMailer

Also known asGHSA-5f37-gxvh-23v6

Published

Dec 30, 2016

Updated

Apr 16, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

37 known

EPSS Exploitation Probability

via FIRST.org ↗

94.4%probability of exploitation in next 30 days

Very High Risk100th percentile-0.02%

EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.

Blast Radius

1 pkg affected

🐘phpmailer/phpmailer

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Packagist packages — download data is not available via public APIs for these ecosystems.

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.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐘Packagist	`phpmailer/phpmailer`	≥ 5.0.0&&< 5.2.18	5.2.18

Exploits & PoCs

Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.

EDB-40968webappsphp✓ Verified

PHPMailer < 5.2.18 - Remote Code Execution

by Dawid Golunski · Dec 26, 2016

Exploit-DB Source

EDB-42221webappsphp

PHPMailer < 5.2.20 with Exim MTA - Remote Code Execution

by phackt_ul · Jun 21, 2017

Exploit-DB Source

EDB-40969webappsphp

PHPMailer < 5.2.20 - Remote Code Execution

by Dawid Golunski · Dec 27, 2016

Exploit-DB Source

EDB-40986webappsphp

PHPMailer < 5.2.20 / SwiftMailer < 5.4.5-DEV / Zend Framework / zend-mail < 2.4.11 - 'AIO' 'PwnScriptum' Remote Code Execution

by Dawid Golunski · Jan 2, 2017

Exploit-DB Source

EDB-41996remotephp

Vanilla Forums < 2.3 - Remote Code Execution

by Dawid Golunski · May 11, 2017

Exploit-DB Source

EDB-41962webappslinux

WordPress Core 4.6 - Remote Code Execution

by Dawid Golunski · May 3, 2017

Exploit-DB Source

EDB-40970webappsphp

PHPMailer < 5.2.18 - Remote Code Execution

by Dawid Golunski · Dec 25, 2016

Exploit-DB Source

EDB-42024remotephp✓ Verified

WordPress Plugin PHPMailer 4.6 - Host Header Command Injection (Metasploit)

by Metasploit · May 17, 2017

Exploit-DB Source

EDB-40974webappsphp

PHPMailer < 5.2.18 - Remote Code Execution

by anarc0der · Dec 29, 2016

Exploit-DB Source

Frequently Asked Questions

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.

O3 Security · Impact-Aware SCA

Is CVE-2016-10033 in your stack?

O3 detects CVE-2016-10033 across Packagist dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.

Scan my stack How O3 SCA works

CVSS Score

9.8/10

CVSS v3 base score

Vector breakdown

AV:Attack Vector

Network

AC:Attack Complexity

Low

PR:Privileges Required

None

UI:User Interaction

None

S:Scope

Unchanged

C:Confidentiality

High

I:Integrity

High

A:Availability

High

Raw vector

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

CWE Classification

Weaponization

OpenSSF Scorecard

Package health score

PHPMailer

6.5/10

Code-Review2/10

Maintained10/10

Vulnerabilities10/10

Dependency-Update-Tool10/10

Branch-Protection3/10

Assessed Jun 8, 2026

Timeline

First exploit

Dec 26, 2016

Disclosed

Dec 30, 2016

KEV added

Jul 7, 2025

Last updated

Apr 16, 2026

Identifiers

CVE-2016-10033

GHSA-5f37-gxvh-23v6

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