CVE-2016-10033: PHPMailer Command Injection Vulnerability

Q: How do I fix CVE-2016-10033?

phpmailer: upgrade to 5.2.18; wordpress: upgrade to newer than 4.7; joomla\!: upgrade to newer than 3.6.5. Exact commands for each OS are on this page.

Q: Is CVE-2016-10033 being exploited?

Yes. CVE-2016-10033 is on the CISA Known Exploited Vulnerabilities list, so treat it as patch-now.

Q: What does CVE-2016-10033 affect?

CVE-2016-10033 affects phpmailer, wordpress, joomla\!. Severity is critical (CVSS 9.8). 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

Q: How urgent is CVE-2016-10033?

Priority 97/100. Critical severity; EPSS top 1%: very likely to be exploited; Exploited in the wild (CISA KEV); Public exploit reference; CISA SSVC: automatable with total technical impact; Remotely exploitable, no login, no user action

Patch now

CRITICAL 9.8EXPLOITEDREMOTEUPGRADEUPGRADEUPGRADE

CVE-2016-10033 is a critical-severity flaw (CVSS 9.8) affecting phpmailer, wordpress, joomla\!, reported as exploited in the wild. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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.

Why this priority

Critical severity
EPSS top 1%: very likely to be exploited
Exploited in the wild (CISA KEV)
Public exploit reference
CISA SSVC: automatable with total technical impact
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	9.8 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	99.7% (top 1%)
CISA exploited list	Yes, fix due 2025-07-28
Weakness	CWE-88
Published	2016-12-30
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: joomla · phpmailer project · wordpress

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2016-12-30 19:59 UTCPublished CVE record published
2025-07-07Exploited Added to the CISA Known Exploited Vulnerabilities list
2025-07-28Deadline CISA due date for US federal agencies to patch
2026-06-17 00:38 UTCUpdated Record last modified

phpmailer project phpmailer UPGRADE

Affected: < 5.2.18

Fixed in: 5.2.18

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy phpmailer || rpm -q phpmailer || phpmailer --version

2. UPGRADE to 5.2.18 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade phpmailer

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade phpmailer

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

wordpress wordpress UPGRADE

Affected: <= 4.7

Fixed in: newer than 4.7

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy wordpress || rpm -q wordpress || wordpress --version

2. UPGRADE to newer than 4.7 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade wordpress

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade wordpress

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

joomla joomla\! UPGRADE

Affected: >= 1.5.0 and <= 3.6.5

Fixed in: newer than 3.6.5

Safe to downgrade to: a release before 1.5.0

1. Check installed version

apt-cache policy joomla || rpm -q joomla || joomla --version

2. UPGRADE to newer than 3.6.5 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade joomla

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade joomla

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

3. If no update is available yet, DOWNGRADE to a release before 1.5.0 (Debian / Ubuntu)

apt-cache madison joomla sudo apt install joomla=<VERSION_BEFORE_1.5.0> sudo apt-mark hold joomla

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list joomla sudo dnf downgrade joomla-<VERSION_BEFORE_1.5.0> sudo dnf versionlock add joomla

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Exact fixes by distribution

Composer (PHP) · phpmailer/phpmailer · FIXED · 5.2.18 · vulnerable: >= 5.0.0, < 5.2.18 · source

composer require "phpmailer/phpmailer:>=5.2.18"

Fedora 46 · root · FIXED · 6.40.04-7.fc46 · FEDORA-2026-7329868400 · source

sudo dnf upgrade --advisory=FEDORA-2026-7329868400

Ubuntu 20.04 · libphp-phpmailer · NOT AFFECTED

Ubuntu 22.04 · libphp-phpmailer · NOT AFFECTED

Debian 12 · libphp-phpmailer · FIXED · 5.2.14+dfsg-2.1

sudo apt update && sudo apt install --only-upgrade libphp-phpmailer dpkg --compare-versions "$(dpkg-query -W -f='${Version}' libphp-phpmailer)" ge "5.2.14+dfsg-2.1" && echo PATCHED || echo STILL-VULNERABLE

Debian 13 · libphp-phpmailer · FIXED · 5.2.14+dfsg-2.1

Public exploits and detection

Public code exists for this CVE. Treat unpatched systems as at risk, and only run PoCs in a lab.

Exploit-DB: WordPress Core 4.6 - Remote Code Execution
Exploit-DB: Vanilla Forums < 2.3 - Remote Code Execution
Exploit-DB: WordPress Plugin PHPMailer 4.6 - Host Header Command Injection (Metasploit)
Exploit-DB: PHPMailer < 5.2.18 - Remote Code Execution
Exploit-DB: PHPMailer < 5.2.18 - Remote Code Execution
Exploit-DB: PHPMailer < 5.2.18 - Remote Code Execution
Exploit-DB: PHPMailer < 5.2.20 - Remote Code Execution
Exploit-DB: PHPMailer < 5.2.20 / SwiftMailer < 5.4.5-DEV / Zend Framework / zend-mail < 2.4.11 - 'AIO' 'PwnScriptum' Remote Code Exe

Verify at the official source NVD · CVE Program · CISA KEV catalog · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2016-10033?

phpmailer: upgrade to 5.2.18; wordpress: upgrade to newer than 4.7; joomla\!: upgrade to newer than 3.6.5. Exact commands for each OS are on this page.

Is CVE-2016-10033 being exploited?

Yes. CVE-2016-10033 is on the CISA Known Exploited Vulnerabilities list, so treat it as patch-now.

What does CVE-2016-10033 affect?

CVE-2016-10033 affects phpmailer, wordpress, joomla\!. Severity is critical (CVSS 9.8). 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

How urgent is CVE-2016-10033?

Priority 97/100. Critical severity; EPSS top 1%: very likely to be exploited; Exploited in the wild (CISA KEV); Public exploit reference; CISA SSVC: automatable with total technical impact; Remotely exploitable, no login, no user action

Software pages

WordPress vulnerabilities · Joomla vulnerabilities

Related CVEs

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CVE-2020-36326 CRITICAL 9.8 UPGRADE UPGRADE PHPMailer 6.1.8 through 6.4.0 allows object injection through Phar Deserialization via addAttachment with a UN
CVE-2020-13625 HIGH 7.5 UPGRADE MITIGATE PHPMailer before 6.1.6 contains an output escaping bug when the name of a file attachment contains a double qu
CVE-2018-19296 HIGH 8.8 UPGRADE MITIGATE PHPMailer before 5.2.27 and 6.x before 6.0.6 is vulnerable to an object injection attack.

References

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