CVE-2020-36326: PHPMailer 6.1.8 through 6.4.0 allows object injection through Phar Deserialization via addAttachment with a UN

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CRITICAL 9.8REMOTEUPGRADEUPGRADE

CVE-2020-36326 is a critical-severity flaw (CVSS 9.8) affecting phpmailer, wordpress. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

PHPMailer 6.1.8 through 6.4.0 allows object injection through Phar Deserialization via addAttachment with a UNC pathname. NOTE: this is similar to CVE-2018-19296, but arose because 6.1.8 fixed a functionality problem in which UNC pathnames were always considered unreadable by PHPMailer, even in safe contexts. As an unintended side effect, this fix eliminated the code that blocked addAttachment exploitation.

Why this priority

Critical severity
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	3.1% (top 12%)
CISA exploited list	No
Weakness	CWE-502
Published	2021-04-28
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: 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

2021-04-28 03:15 UTCPublished CVE record published
2026-06-17 03:15 UTCUpdated Record last modified

phpmailer project phpmailer UPGRADE

Affected: >= 6.1.8 and <= 6.4.0

Fixed in: newer than 6.4.0

Safe to downgrade to: a release before 6.1.8

1. Check installed version

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

2. UPGRADE to newer than 6.4.0 (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.

3. If no update is available yet, DOWNGRADE to a release before 6.1.8 (Debian / Ubuntu)

apt-cache madison phpmailer sudo apt install phpmailer=<VERSION_BEFORE_6.1.8> sudo apt-mark hold phpmailer

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

dnf --showduplicates list phpmailer sudo dnf downgrade phpmailer-<VERSION_BEFORE_6.1.8> sudo dnf versionlock add phpmailer

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.

wordpress wordpress UPGRADE

Affected: >= 3.7 and < 3.7.36 · >= 3.8 and < 3.8.36 · >= 3.9 and < 3.9.34 · >= 4.0 and < 4.0.33 · >= 4.1 and < 4.1.33 · >= 4.2 and < 4.2.30 · >= 4.3 and < 4.3.26 · >= 4.4 and < 4.4.25

Fixed in: 3.7.36, 3.8.36, 3.9.34, 4.0.33, 4.1.33, 4.2.30, 4.3.26, 4.4.25, 4.5.24, 4.6.21, 4.7.21, 4.8.17, 4.9.18, 5.0.13, 5.1.10, 5.2.11, 5.3.8, 5.4.6, 5.5.5, 5.6.4, 5.7.2

Safe to downgrade to: a release before 3.7

1. Check installed version

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

2. UPGRADE to 3.7.36 (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.

3. If no update is available yet, DOWNGRADE to a release before 3.7 (Debian / Ubuntu)

apt-cache madison wordpress sudo apt install wordpress=<VERSION_BEFORE_3.7> sudo apt-mark hold wordpress

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

dnf --showduplicates list wordpress sudo dnf downgrade wordpress-<VERSION_BEFORE_3.7> sudo dnf versionlock add wordpress

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.

Verify at the official source NVD · CVE Program · 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-2020-36326?

phpmailer: upgrade to newer than 6.4.0; wordpress: upgrade to 3.7.36, 3.8.36, 3.9.34, 4.0.33, 4.1.33, 4.2.30, 4.3.26, 4.4.25, 4.5.24, 4.6.21, 4.7.21, 4.8.17, 4.9.18, 5.0.13, 5.1.10, 5.2.11, 5.3.8, 5.4.6, 5.5.5, 5.6.4, 5.7.2. Exact commands for each OS are on this page.

Is CVE-2020-36326 being exploited?

CVE-2020-36326 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2020-36326 affect?

CVE-2020-36326 affects phpmailer, wordpress. Severity is critical (CVSS 9.8). PHPMailer 6.1.8 through 6.4.0 allows object injection through Phar Deserialization via addAttachment with a UNC pathname. NOTE: this is similar to CVE-2018-19296, but arose because 6.1.8 fixed a functionality problem in which UNC pathnames

How urgent is CVE-2020-36326?

Priority 61/100. Critical severity; Remotely exploitable, no login, no user action

Software pages

WordPress vulnerabilities

Related CVEs

CVE-2021-3603 HIGH 8.1 UPGRADE MITIGATE PHPMailer 6.4.1 and earlier contain a vulnerability that can result in untrusted code being called (if such co
CVE-2021-34551 HIGH 8.1 UPGRADE MITIGATE PHPMailer before 6.5.0 on Windows allows remote code execution if lang_path is untrusted data and has a UNC pa
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.
CVE-2017-5223 MEDIUM 5.5 UPGRADE An issue was discovered in PHPMailer before 5.2.22

References

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