CVE-2021-44618: A Server-side Template Injection (SSTI) vulnerability exists in Nystudio107 Seomatic 3.4.12 in src/helpers/Url

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CRITICAL 9.8REMOTEDOWNGRADE

CVE-2021-44618 is a critical-severity flaw (CVSS 9.8) affecting seomatic. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

A Server-side Template Injection (SSTI) vulnerability exists in Nystudio107 Seomatic 3.4.12 in src/helpers/UrlHelper.php via the host header.

Why this priority

Critical severity
Remotely exploitable, no login, no user action

No fix is published yet: follow the downgrade or mitigation steps.

Risk facts

CVSS score	9.8 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	1.4% (top 28%)
CISA exploited list	No
Weakness	CWE-94
Published	2022-03-11
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: nystudio107

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

Am I affected?

Timeline

2022-03-11 16:15 UTCPublished CVE record published
2026-06-17 04:12 UTCUpdated Record last modified

nystudio107 seomatic DOWNGRADE

Affected: 3.4.12

Fixed in: no fixed release known

Safe to downgrade to: a release before 3.4.12

1. Check installed version

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

2. No fixed release: DOWNGRADE to a release before 3.4.12 (Debian / Ubuntu)

apt-cache madison seomatic sudo apt install seomatic=<VERSION_BEFORE_3.4.12> sudo apt-mark hold seomatic

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list seomatic sudo dnf downgrade seomatic-<VERSION_BEFORE_3.4.12> sudo dnf versionlock add seomatic

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-2021-44618?

seomatic: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2021-44618 being exploited?

CVE-2021-44618 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-2021-44618 affect?

CVE-2021-44618 affects seomatic. Severity is critical (CVSS 9.8). A Server-side Template Injection (SSTI) vulnerability exists in Nystudio107 Seomatic 3.4.12 in src/helpers/UrlHelper.php via the host header.

How urgent is CVE-2021-44618?

Priority 57/100. Critical severity; Remotely exploitable, no login, no user action

Software pages

PHP vulnerabilities

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References

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