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NVD / CVE Program· CNA GitHub_M

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

HighCVSS 8.8 · v3.1—No exploit Fix available

Noroxi assessment

Priority: Monitor (action score 36/100)

  • The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
  • Probability of exploitation in the next 30 days: 2.1% (FIRST EPSS); higher than 82.3% of all records.
  • Anyone who can reach it over the internet can trigger it. A low-privileged account is enough. No user action is required. No special conditions are required; it is repeatable.
  • Fixed version: smarty-php smarty 3.1.43.

Low priority for now. Upgrade to smarty-php smarty 3.1.43 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

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
Jan 10, 2022
Updated
Jun 16, 2026
EPSS
2.1% · 82th percentile

Report tools

JSON

Action score

36

Monitor

Low priority for now.

CVSS
35 / 40 · 8.8 / 10
CISA KEV
0 / 30 · Not listed
EPSS
1 / 30 · 2.1%

CISA SSVC decision

Exploitation
none
Automatable
no
Technical impact
total

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD
8.8
CNA · GitHub_M
8.8
agree

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Get told when this record changes

  • Not in KEV: no record of exploitation in the wild
  • No public exploit code on record
  • A fix has been released

If any of these changes, we'll tell you in the daily email digest.

Follow CVE-2021-21408

When you'll hear from us

  • when it enters CISA KEV
  • when exploit code appears or is weaponized
  • when the record is updated (including a fixed version)
  • when EPSS rises 20 points in a week

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

VendorProduct
smartysmarty
debiandebian linux
fedoraprojectfedora

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

  • debian debian linux10.0
  • debian debian linux11.0
  • debian debian linux9.0
  • fedoraproject fedora36
  • fedoraproject fedora37
  • smarty smarty4.0.0 and later · before 4.0.3
  • smarty smartybefore 3.1.43

Versions reported by the vendor

Affected version ranges reported by the assigning authority (GitHub_M). Independent of NVD's CPE analysis and usually ahead of it.

  • smarty-php smarty

    • < 3.1.43, >= 4.0.0, < 4.0.3affected

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
Debian:10smarty3before 3.1.33+20180830.1.3a78a21f+selfpack1-1+deb10u13.1.33+20180830.1.3a78a21f+selfpack1-1+deb10u1
Debian:11smarty3before 3.1.39-2+deb11u13.1.39-2+deb11u1
Debian:12smarty3before 3.1.45-13.1.45-1
Debian:12smarty4before 4.1.1-14.1.1-1
Debian:9smarty3before 3.1.31+20161214.1.c7d42e4+selfpack1-2+deb9u53.1.31+20161214.1.c7d42e4+selfpack1-2+deb9u5
Packagistsmarty/smartyfrom 4.0.0 · before 4.0.34.0.3
Packagistsmarty/smartybefore 3.1.433.1.43

Same product

smarty: all records

Other highest-scoring records for the same primary product.

  • CVE-2021-26120Smarty before 3.1.39 allows code injection via an unexpected function name after a {function name= substring.
    64This week
  • CVE-2009-1669The smarty_function_math function in libs/plugins/function.math.php in Smarty 2.6.22 allows context-dependent attackers to execute…
    44Plan
  • CVE-2010-4727Smarty before 3.0.0 beta 7 does not properly handle the <?php and ?> tags, which has unspecified impact and remote attack vectors.
    41Plan

Published before and after this one in the same product

  • ← EarlierCVE-2011-1028Nov 20, 2019 · The $smarty.template variable in Smarty3 allows attackers to possibly execute arbitrary PHP code via the…
    39Monitor
  • ← EarlierCVE-2021-26119Feb 21, 2021 · Smarty before 3.1.39 allows a Sandbox Escape because $smarty.template_object can be accessed in sandbox mode.
    33Monitor
  • Later →CVE-2021-29454Jan 10, 2022 · Sandbox Escape by math function in smarty
    36Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
smarty-php smarty3.1.43 · descriptionVendor (CNA)
debian:smarty33.1.45-1 · Debian:12Package registry (OSV)
debian:smarty44.1.1-1 · Debian:12Package registry (OSV)
Packagist:smarty/smarty3.1.43Package registry (OSV)
Packagist:smarty/smarty4.0.3Package registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

No history yet (it accumulates with the daily EPSS job).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

No credits in the CNA record.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

No nightly-computed relations.

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

Technical details

Attack conditions

  • Anyone who can reach it over the internet can trigger it.
  • A low-privileged account is enough.
  • No user action is required.
  • No special conditions are required; it is repeatable.

If successful

Confidentiality
high · data can be read
Integrity
high · data or configuration can be modified
Availability
high · the service can be disrupted
Attack vector
Network
Attack complexity
Low
Privileges required
Low
User interaction
None
Scope
Unchanged
Confidentiality impact
High
Integrity impact
High
Availability impact
High

Weakness class (CWE)

CWE-20 · Improper Input Validation

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

nvd-primary

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

Change log

  1. Fix✗ → ✓

For records you follow, these changes also arrive as notifications. →

References

Show all references (8 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records