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Actively exploited in the wild. This CVE is on the CISA Known Exploited Vulnerabilities list — treat remediation as urgent. Federal remediation due by 28 Jul 2025.
WordPressCMS

CVE-2016-10033

CRITICAL · 9.8 CVSS v3.1 Published 2016-12-30
Fix available
A fix is available. Upgrade to 5.2.18 or later.
See remediation →
100/100
Remediation priority · Urgent
In the wild High EPSS Public exploit Remotely reachable No privileges Zero-click Patch available

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
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.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

Command injection vulnerability in PHPMailer before 5.2.18 allows remote attackers to execute arbitrary code by injecting additional parameters into the mail() function through a backslash double quote in the Sender property, bypassing intended parameter sanitization.

MitigationUpgrade PHPMailer to version 5.2.18 or later which contains the fix. If immediate upgrade is not feasible, validate and sanitize all user-supplied email properties before passing them to PHPMailer.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
WordPressCMS
Affected:<= 4.7
Joomla\!Application
Affected:>= 1.5.0, <= 3.6.5
PhpmailerApplication
Affected:< 5.2.18

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

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

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Locate PHPMailer library version
    Find the class.phpmailer.php file in your application (check vendor directories, wp-includes for WordPress, libraries/src/Mail for Joomla, or vendor/phpmailer for standalone). Open the file and look for a version constant or check the file header comment for version information.
    Affected if The version is below 5.2.18 (e.g., 5.2.17 or earlier)
  2. Confirm the isMail transport is in use
    Search your codebase for PHPMailer initialization that uses the 'isMail' property or the mail() function. In WordPress, this is the default transport used by wp_mail(). In Joomla, check configuration for mail settings. Look for code setting $mailer->isMail() or confirm the mail system is set to PHP mail.
    Affected if The application uses the default PHP mail() function transport (isMail) rather than SMTP
  3. Check WordPress bundled PHPMailer version
    If running WordPress, locate wp-includes/class-phpmailer.php and check the version number in the file header or version constant. WordPress 4.7 and earlier shipped with vulnerable PHPMailer versions.
    Affected if WordPress version is 4.7 or lower and the bundled class-phpmailer.php shows a version below 5.2.18
  4. Check Joomla bundled PHPMailer version
    If running Joomla, locate libraries/src/Mail/Mail.php or libraries/phpmailer/phpmailer.php and check the PHPMailer version it loads. Joomla bundles PHPMailer in its libraries folder.
    Affected if Joomla version is between 1.5.0 and 3.6.5 inclusive, and the bundled PHPMailer is below 5.2.18

You are affected if your application uses PHPMailer version below 5.2.18 with the default PHP mail() transport (isMail), which is the default for WordPress <= 4.7 and Joomla <= 3.6.5.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 5.2.18 or later
Fixed in 5.2.18
Vendor patch seclists.org →
Interim mitigation

Upgrade PHPMailer to version 5.2.18 or later which contains the fix. If immediate upgrade is not feasible, validate and sanitize all user-supplied email properties before passing them to PHPMailer.

Recommended fix High confidence

PHPMailer 5.2.18 or later

  1. Identify the PHPMailer version in use by examining the codebase or vendor dependencies
  2. For direct PHPMailer installations: download and install PHPMailer version 5.2.18 or later from the official GitHub repository
  3. For WordPress: upgrade to WordPress 4.7.1 or later which includes the patched PHPMailer library
  4. For Joomla: upgrade to Joomla 3.6.6 or later which includes the patched PHPMailer library
  5. After upgrading, verify the Sender property input is properly validated and escaped before being passed to the mail() function

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in WordPress Exploited in the wild — priority engagement
  • Consultation3.0 h
  • Implementation4.0 h
  • Testing2.0 h
  • Review / QA2.0 h
11.0 hours of engineering $1,980
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An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $3,168.

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2016-10033 in production — separate from our analysis above.

No notes yet

Be the first to add a field note for this CVE — a mitigation you’ve verified, a version caveat, or a link to a working fix. Sign in above to contribute.

What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data