How severe is CVE-2021-21408?

CVE-2021-21408 has a CVSS 3.x base score of 8.8, rated high severity. It is exploitable over network with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2021-21408 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (81st percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-21408?

CVE-2021-21408 primarily affects Smarty. In total, 6 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2021-21408?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

When was CVE-2021-21408 published?

CVE-2021-21408 was published on 2022-01-10 and last updated on 2026-06-17.

CVE-2021-21408

CVE-2021-21408 is a high-severity vulnerability in Smarty with a CVSS 3.x base score of 8.8. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-20.

Key facts

Severity: High (CVSS 3.x base score 8.8)
CVSS v2: 6.5
EPSS exploit prediction: 2% (81st percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-20
Affected product: Smarty
Published: 2022-01-10
Last modified: 2026-06-17

Description

Smarty is a template engine for PHP, facilitating the separation of presentation (HTML/CSS) from application logic. Prior to versions 3.1.43 and 4.0.3, template authors could run restricted static php methods. Users should upgrade to version 3.1.43 or 4.0.3 to receive a patch.

Frequently asked questions

What is CVE-2021-21408?: Smarty is a template engine for PHP, facilitating the separation of presentation (HTML/CSS) from application logic. Prior to versions 3.1.43 and 4.0.3, template authors could run restricted static php methods. Users should upgrade to version 3.1.43 or 4.0.3 to receive a patch.
How severe is CVE-2021-21408?: CVE-2021-21408 has a CVSS 3.x base score of 8.8, rated high severity. It is exploitable over network with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2021-21408 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (81st percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-21408?: CVE-2021-21408 primarily affects Smarty. In total, 6 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2021-21408?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2021-21408 published?: CVE-2021-21408 was published on 2022-01-10 and last updated on 2026-06-17.

References

Affected products (6)

cpe:2.3:a:smarty:smarty:*:*:*:*:*:*:*:*
cpe:2.3:o:debian:debian_linux:9.0:*:*:*:*:*:*:*
cpe:2.3:o:debian:debian_linux:10.0:*:*:*:*:*:*:*
cpe:2.3:o:debian:debian_linux:11.0:*:*:*:*:*:*:*
cpe:2.3:o:fedoraproject:fedora:36:*:*:*:*:*:*:*
cpe:2.3:o:fedoraproject:fedora:37:*:*:*:*:*:*:*

More vulnerabilities in Smarty

CVE-2010-4727 — Critical (CVSS 10.0): Smarty before 3.0.0 beta 7 does not properly handle the <?php and ?> tags, which has unspecified impact and remote…
CVE-2010-4726 — Critical (CVSS 10.0): Unspecified vulnerability in the math plugin in Smarty before 3.0.0 RC1 has unknown impact and remote attack vectors.…
CVE-2010-4725 — Critical (CVSS 10.0): Smarty before 3.0.0 RC3 does not properly handle an on value of the asp_tags option in the php.ini file, which has…
CVE-2010-4724 — Critical (CVSS 10.0): Multiple unspecified vulnerabilities in the parser implementation in Smarty before 3.0.0 RC3 have unknown impact and…
CVE-2010-4722 — Critical (CVSS 10.0): Unspecified vulnerability in the fetch plugin in Smarty before 3.0.2 has unknown impact and remote attack vectors.
CVE-2009-5052 — Critical (CVSS 10.0): Multiple unspecified vulnerabilities in Smarty before 3.0.0 beta 6 have unknown impact and attack vectors.

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