CVE-2021-21408 | Access to restricted PHP code by dynamic static class access in smarty

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.

Published: 2022-01-10 Last update: 2024-11-21 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2021-21408 is rated Moderate Risk (57.8/100): CVSS High severity, with medium exploitation likelihood (EPSS 0.47%). Review affected assets and schedule remediation.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2021-21408

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-01-25 0.32% 0.47% +0.15%
2 2025-11-21 2.21% 0.32% -1.90%
3 2025-11-18 — 2.21% —

Full EPSS history (19 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-21408

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
8.8 3.1 HIGH
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:L)
A normal user session is enough; they don’t have to be admin.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 2.8 5.9 [email protected]
8.8 3.1 HIGH
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:L)
A normal user session is enough; they don’t have to be admin.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 2.8 5.9 [email protected]
6.5 2.0 MEDIUM
AV:N/AC:L/Au:S/C:P/I:P/A:P Click to expand
Access vector (AV:N)
Can be exploited remotely over network reachability.
Access complexity (AC:L)
Exploitation conditions are straightforward and predictable.
Authentication (AU:S)
A single authentication is required.
Confidentiality impact (C:P)
Partial confidentiality impact.
Integrity impact (I:P)
Partial integrity impact.
Availability impact (A:P)
Partial availability impact.
 8.0 6.4 [email protected]

Weakness enumeration for CVE-2021-21408

GitHub Security Advisory for CVE-2021-21408

GHSA-4h9c-v5vg-5m6m · Severity: high · Ecosystem: composer — Access to restricted PHP code by dynamic static class access in smarty

OS Trackers for CVE-2021-21408

vendor priority summary link
debian not yet assigned CVE-2021-21408 not yet assigned priority: Debian including 2 source packages (smarty3, smarty4), 9 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 9. https://security-tracker.debian.org/tracker/CVE-2021-21408
gentoo normal CVE-2021-21408: 1 GLSA(s) (202209-09), 1 atom(s) (dev-php/smarty); latest impact normal. https://bugs.gentoo.org/buglist.cgi?quicksearch=CVE-2021-21408
ubuntu medium CVE-2021-21408 medium priority: Ubuntu including 1 source packages (smarty3), 14 status rows across 14 suites (bionic, focal, hirsute, impish, jammy, kinetic, lunar, mantic, noble, oracular, plucky, trusty, upstream, xenial): released 12, DNE 1, ignored 1. https://ubuntu.com/security/CVE-2021-21408

Affected software / configurations for CVE-2021-21408

Vendor Product Version Raw CPE
smarty smarty < 3.1.43 cpe:2.3:a:smarty:smarty:*:*:*:*:*:*:*:*
smarty smarty >= 4.0.0, < 4.0.3 cpe:2.3:a:smarty:smarty:*:*:*:*:*:*:*:*
debian debian_linux 9.0 cpe:2.3:o:debian:debian_linux:9.0:*:*:*:*:*:*:*
debian debian_linux 10.0 cpe:2.3:o:debian:debian_linux:10.0:*:*:*:*:*:*:*
debian debian_linux 11.0 cpe:2.3:o:debian:debian_linux:11.0:*:*:*:*:*:*:*
fedoraproject fedora 36 cpe:2.3:o:fedoraproject:fedora:36:*:*:*:*:*:*:*
fedoraproject fedora 37 cpe:2.3:o:fedoraproject:fedora:37:*:*:*:*:*:*:*

References for CVE-2021-21408

URL Tags
https://github.com/smarty-php/smarty/commit/19ae410bf56007a5ef24441cdc6414619cfaf664 Patch Third Party Advisory
https://github.com/smarty-php/smarty/releases/tag/v3.1.43 Release Notes Third Party Advisory
https://github.com/smarty-php/smarty/releases/tag/v4.0.3 Release Notes Third Party Advisory
https://github.com/smarty-php/smarty/security/advisories/GHSA-4h9c-v5vg-5m6m Third Party Advisory
https://lists.debian.org/debian-lts-announce/2022/05/msg00005.html Mailing List Third Party Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/BRAJVDRGCIY5UZ2PQHKDTT7RMKG6WJQQ/
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/L777JIBIWJV34HS7LXPIDWASG7TT4LNI/
https://security.gentoo.org/glsa/202209-09 Third Party Advisory
https://www.debian.org/security/2022/dsa-5151 Third Party Advisory
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