CVE-2021-29454 Sandbox Escape by math function in smarty

What is CVE-2021-29454?

CVE-2021-29454 is a high-severity code injection vulnerability in Debian Debian Linux, published on 10 Jan 2022. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

Official description

Smarty is a template engine for PHP, facilitating the separation of presentation (HTML/CSS) from application logic. Prior to versions 3.1.42 and 4.0.2, template authors could run arbitrary PHP code by crafting a malicious math string. If a math string was passed through as user provided data to the math function, external users could run arbitrary PHP code by crafting a malicious math string. Users should upgrade to version 3.1.42 or 4.0.2 to receive a patch.

Weakness: CWE-74

Which versions are affected by CVE-2021-29454?

4 open source packages ship an affected version, including smarty/smarty. It affects 3 products.

Products include Debian Debian Linux, Fedoraproject Fedora, Smarty Smarty.

How do I fix CVE-2021-29454?

Upgrade smarty/smarty to a fixed version for your release line: 3.1.42 or 4.0.2.

Upgrade, and never evaluate templates, expressions or code built from user input. More about Code injection.

Is CVE-2021-29454 being exploited?

There is no known exploitation of CVE-2021-29454 in the wild and no public exploit code.

Other vulnerabilities in Debian Debian Linux

• CVE-2015-3306 ProFTPD Improper Access Control Exploited Critical 10.0
• CVE-2025-49113 RoundCube Webmail Deserialization of Untrusted Data Exploited Critical 9.9
• CVE-2026-24061 GNU InetUtils Argument Injection Exploited Critical 9.8
• CVE-2025-39682 Linux Kernel Improper Check for Unusual or Exceptional Conditions Exploited Critical 9.8
• CVE-2024-9680 Mozilla Firefox Use-After-Free Exploited Critical 9.8

All Debian Debian Linux vulnerabilities

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as DEBIAN-CVE-2021-29454, GHSA-29gp-2c3m-3j6m, UBUNTU-CVE-2021-29454.