CVE-2021-29454 is a high-severity (CVSS 8.8) CWE-74 vulnerability in smarty/smarty. A fix is available for smarty/smarty — see the affected versions and patch details below.
Sandbox Escape by math function in smarty
Exploitation Status
No confirmed exploitation observed yet
- A successful exploit gives an attacker total control of the affected component, not partial access.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2021-29454.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2021-29454 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 385,738 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
Real-World Exposure
smarty/smarty🐘smarty/smartyReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Packagist packages — download data is not available via public APIs for these ecosystems.
Description
Impact
Template authors could run arbitrary PHP code by crafting a malicious math string. If a math string is passed through as user provided data to the math function, external users could run arbitrary PHP code by crafting a malicious math string.
Patches
Please upgrade to 4.0.2 or 3.1.42 or higher.
References
See documentation on Math function.
For more information
If you have any questions or comments about this advisory please open an issue in the Smarty repo
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐘Packagist | smarty/smarty | all versions | 3.1.42composer require smarty/smarty:^3.1.42 |
| 🐘Packagist | smarty/smarty | ≥ 4.0.0&&< 4.0.2 | 4.0.2composer require smarty/smarty:^4.0.2 |
Affected Products
debian linuxdebianfedorafedoraprojectsmartysmartyDetection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for smarty/smarty, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update smarty/smarty to 3.1.42 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-29454 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
Frequently Asked Questions
Is CVE-2021-29454 in your dependencies?
Find it across Packagist, including transitive dependencies.