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 5.2.18 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2016-10033 is resolved across your whole dependency graph.

How do I detect CVE-2016-10033 in my Packagist dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for phpmailer/phpmailer, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2016-10033 if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

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 99.7%, 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 October 24, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐘

🐘 Packagist

CISA KEV · ACTIVELY EXPLOITED

CRITICAL severity

CVE-2016-10033 — phpmailer

CRITICAL

CVE-2016-10033 is a critical-severity (CVSS 9.8) CWE-88 vulnerability in phpmailer/phpmailer. It is in CISA's Known Exploited Vulnerabilities catalog (added 2025-07-07) — treat it as actively exploited and patch now. A fix is available for phpmailer/phpmailer — see the affected versions and patch details below.

Remote code execution in PHPMailer

Also known asGHSA-5f37-gxvh-23v6

Published

Dec 30, 2016

Updated

Oct 24, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

37 known

Exploitation data as of Oct 26, 2026 · OSV.dev, NVD, CISA KEV, FIRST.org (EPSS)

Exploitation Status

Actively exploited in the wild

Confirmed by CISA's Known Exploited Vulnerabilities catalog on 2025-07-07. Federal agencies were required to remediate by 2025-07-28.
CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
A successful exploit gives an attacker total control of the affected component, not partial access.

Exploitation and automatability from CISA (KEV catalog and SSVC triage) for CVE-2016-10033.

EPSS Exploitation Probability

via FIRST.org ↗

99.7%probability of exploitation in next 30 days

Very High Risk0.00%

Lower risk than most CVEs100th percentile — riskier than 100% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

CVE-2016-10033 by exploitation likelihood (EPSS) against impact (CVSS). In the shaded patch-first corner (EPSS 50%+, CVSS 7.0+).

Where this sits among everything scored

Of 396,966 CVEs with a current EPSS score, this one falls in the ≥ 90% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

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

Impact

The mailSend function in the default 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.

Patches

Fixed in 5.2.18

Workarounds

Filter and validate user input before passing it to internal functions.

References

https://nvd.nist.gov/vuln/detail/CVE-2016-10033 Related to a follow-on issue in https://nvd.nist.gov/vuln/detail/CVE-2016-10045

For more information

If you have any questions or comments about this advisory:

Open a private issue in the PHPMailer project

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐘Packagist	`phpmailer/phpmailer`	≥ 5.0.0&&< 5.2.18	5.2.18`composer require phpmailer/phpmailer:^5.2.18`

Affected Products

3 products · 3 configurations

Application

joomla\!joomla

≥ 1.5.0 && ≤ 3.6.5

range

Application

phpmailerphpmailer_project

< 5.2.18

range

Application

wordpresswordpress

≤ 4.7

range

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-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-42024remotephp✓ Verified

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

by Metasploit · May 17, 2017

Exploit-DB Source

EDB-40970webappsphp

PHPMailer < 5.2.18 - Remote Code Execution

by Dawid Golunski · Dec 25, 2016

Exploit-DB Source

EDB-41996remotephp

Vanilla Forums < 2.3 - Remote Code Execution

by Dawid Golunski · May 11, 2017

Exploit-DB Source

EDB-40974webappsphp

PHPMailer < 5.2.18 - Remote Code Execution

by anarc0der · Dec 29, 2016

Exploit-DB Source

EDB-40969webappsphp

PHPMailer < 5.2.20 - Remote Code Execution

by Dawid Golunski · Dec 27, 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-41962webappslinux

WordPress Core 4.6 - Remote Code Execution

by Dawid Golunski · May 3, 2017

Exploit-DB Source

EDB-40968webappsphp✓ Verified

PHPMailer < 5.2.18 - Remote Code Execution

by Dawid Golunski · Dec 26, 2016

Exploit-DB Source

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for phpmailer/phpmailer, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update phpmailer/phpmailer to 5.2.18 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2016-10033 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

How to detect CVE-2016-10033

A community-maintained Nuclei template exists for this CVE. You can scan for it directly:

nuclei -id cve-2016-10033 -u https://target

Template: WordPress PHPMailer < 5.2.18 - Remote Code Execution
Severity: critical
Impact: Successful exploitation of this vulnerability can lead to unauthorized remote code execution on the affected WordPress website.
Remediation: Upgrade PHPMailer to version 5.2.18 or higher to mitigate this vulnerability.

Template by ProjectDiscovery nuclei-templates (princechaddha), MIT licensed. View the full template. Scan only systems you are authorised to test.

Frequently Asked Questions

### Impact The `mailSend` function in the default `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. ### Patches Fixed in 5.2.18 ### Workarounds Filter and validate user input before passing it to internal functions. ### References https://nvd.nist.gov/vuln/detail/CVE-2016-10033 Related to a follow-on issue in https://nvd.nist.gov/vuln/detail/CVE-2016-10045 ### For more information If you have any questions or co

O3 Security · Impact-Aware SCA

Is CVE-2016-10033 in your dependencies?

Find it across Packagist, including transitive dependencies.

Scan my dependencies How O3 SCA works

CVSS Score

9.8/10CVSS v3 base

Vector breakdown

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

High

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-Review3/10

Maintained10/10

Vulnerabilities10/10

Branch-Protection3/10

Dependency-Update-Tool10/10

Assessed Oct 26, 2026

Timeline

Disclosed

Dec 30, 2016

First exploit

Jan 2, 2017

2 days after disclosure — rapid exploitation

KEV added

Jul 7, 2025

Last updated

Oct 24, 2026

Identifiers

CVE-2016-10033

GHSA-5f37-gxvh-23v6

Related vulnerabilities

This CVE is critical severity; 1 of 8 other CVEs affecting phpmailer/phpmailer is rated as high or higher (top: critical).

CVE-2007-3215CVE-2006-5734CVE-2012-0796CVE-2008-5619CVE-2021-3603CVE-2021-34551CVE-2020-36326CVE-2020-13625

Provenance

Sources

OSV.devNVDCISA KEVFIRST.org (EPSS)

Last verifiedOct 24, 2026