CVE-2016-10033
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.
do firstApply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
Can a WAF block it? Partly. The attack involves sending a crafted HTTP request with a Sender property containing a backslash double quote to exploit the mailSend function. This unusual character sequence in the Sender field could be detected by a WAF, but it might overlap with some legitimate uses, making filtering only partly reliable. A custom WAF rule can filter Sender property containing a backslash double quote sequence, but attackers can vary the request. No tracked WAF vendor has published a rule for this CVE yet.
What a custom rule would match: Sender property containing a backslash double quote sequence
Also consider: patch · custom WAF rule
Based on an AI reading of the CVE description, and no vendor rule found yet. We check Cloudflare, AWS, Google Cloud Armor and Azure; for Akamai, Imperva, Fastly, F5, ask your vendor.
Is CVE-2016-10033 being exploited?
Yes. CVE-2016-10033 appears in CISA's Known Exploited Vulnerabilities catalog, which means exploitation in the wild has been confirmed and reported. Treat it as active rather than theoretical, and patch it ahead of higher-scoring vulnerabilities that carry no exploitation evidence.
How severe is CVE-2016-10033?
CVE-2016-10033 is rated Critical with a CVSS score of 9.8. Severity describes how bad exploitation would be, not how likely it is: pair it with exploitation evidence before deciding what to patch first.
Is there a patch for CVE-2016-10033?
Yes. A fix has been recorded for CVE-2016-10033. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2016-10033 affect?
CVE-2016-10033 affects phpmailer_project:phpmailer, wordpress:wordpress, joomla:joomla\!. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
public exploits
Public exploit code: 9 on Exploit-DB · 2 Metasploit modules · 17 GitHub proofs of concept · 1 Nuclei template
- PHPMailer < 5.2.20 with Exim MTA - Remote Code Execution · webapps · 21 Jun 2017
- WordPress Plugin PHPMailer 4.6 - Host Header Command Injection (Metasploit) · remote · 17 May 2017 · verified
- Vanilla Forums < 2.3 - Remote Code Execution · remote · 11 May 2017
- WordPress Core 4.6 - Remote Code Execution · webapps · 3 May 2017
- exploit/unix/webapp/wp_phpmailer_host_header · exploit · average
- exploit/multi/http/phpmailer_arg_injection · exploit · manual
- WordPress PHPMailer < 5.2.18 - Remote Code Execution · detection template · critical
- opsxcq/exploit-CVE-2016-10033 · 408 ★
- GeneralTesler/CVE-2016-10033 · 9 ★
- Zenexer/safeshell · 8 ★
- 0x00-0x00/CVE-2016-10033 · 6 ★
Listed so you can judge urgency, not as a recommendation to run anything. GitHub “proofs of concept” are unvetted: some are fake or carry malware. Exploit-DB marks the entries its staff verified.
cisa ssvc
- exploitation
- active
- automatable
- yes
- technical impact
- total
Assessed by CISA 17 Jul 2025 (SSVC 2.0.3).
timeline
- 25 Dec 2016First public exploit or proof of concept
- 30 Dec 2016Published · 6 days later
- 7 Jul 2025Added to CISA KEV (exploited in the wild) · 3,110 days (about 9 years) later
- 17 Jul 2025CISA SSVC assessment: exploitation active · 10 days later
- 28 Jul 2025CISA remediation due date (US federal agencies) · 11 days later
- 21 Oct 2025CVE record last updated · 86 days (about 3 months) later
- 2 Nov 2026Analysed by vulneraibility.com · 377 days (about 1 year) later
also known as
- Exploitexploit-db.com /exploits/42221/
- Exploitexploit-db.com /exploits/40969/
- Exploitexploit-db.com /exploits/41962/
- Exploitexploit-db.com /exploits/40968/
- Exploitexploit-db.com /exploits/40974/
- Exploitexploit-db.com /exploits/40986/
- Exploitexploit-db.com /exploits/40970/
- Exploitexploit-db.com /exploits/41996/
Show 14 more
- Exploitexploit-db.com /exploits/42024/
- Linkpacketstormsecurity.com /files/140350/PHPMailer-Sendmail-Argument-Injection.html
- Linkdrupal.org /psa-2016-004
- Linklegalhackers.com /advisories/PHPMailer-Exploit-Remote-Code-Exec-CVE-2016-10033-Vuln.html
- Linkgithub.com /PHPMailer/PHPMailer/releases/tag/v5.2.18
- Linksecurityfocus.com /archive/1/539963/100/0/threaded
- Linkgithub.com /PHPMailer/PHPMailer/wiki/About-the-CVE-2016-10033-and-CVE-2016-10045-vulnerabil
- Linkpacketstormsecurity.com /files/140291/PHPMailer-Remote-Code-Execution.html
- Linkrapid7.com /db/modules/exploit/multi/http/phpmailer_arg_injection
- Linkseclists.org /fulldisclosure/2016/Dec/78
- Linksecurityfocus.com /bid/95108
- Linksecuritytracker.com /id/1037533
- Linkdeveloper.joomla.org /security-centre/668-20161205-phpmailer-security-advisory.html
- Linkcisa.gov /known-exploited-vulnerabilities-catalog?field_cve=CVE-2016-10033
sources
- CVE List (CVE.org): description, affected versions, references; CVE Terms of Use
- NVD: CVSS and CPE data
- CISA KEV catalog: exploitation, date added, due date
- CISA Vulnrichment (ADP): SSVC decision points
- FIRST EPSS: exploit probability and percentile
- Exploit-DB: published exploits
- Metasploit Framework: exploit and scanner modules
- Nuclei templates: detection templates
- PoC-in-GitHub: GitHub repositories that claim a proof of concept
- OSV: advisory aliases and downstream package versions
- Summary, impact and triage tags: written by our AI analysis pipeline from the sources above. Check them against the sources.