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Code Injection Vulnerability in Pybars3 and Pybars4

Code Injection Vulnerability in Pybars3 and Pybars4

First seen 31 Oct 2026, 06:42 UTC • •
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ThreatCluster AI
ThreatCluster •October 31, 2026 at 08:42 UTC
  • •Pybars3 and Pybars4 are vulnerable to code injection leading to RCE.
  • •No patches are available for Pybars3, and Pybars4 remains unpatched.
  • •Proof-of-concept code for exploitation is publicly available.

Pybars3 (up to version 0.9.7) and Pybars4 (up to version 0.9.13) are vulnerable to a code injection flaw that allows attackers to execute arbitrary code through specially crafted template strings. This vulnerability arises from improper escaping of data keys containing special characters, enabling an attacker to control the template string and achieve remote code execution (RCE) in the context of the Python application. The original Pybars implementation is not affected, nor are JavaScript Handlebars or other independent implementations. Currently, no fix has been provided for Pybars3, while Pybars4 remains vulnerable as well. Proof-of-concept (PoC) code demonstrating the exploit has been released. Security professionals are advised to assess their use of these libraries immediately.

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Timeline

2026-10-31
Vulnerability disclosed
Pybars3 and Pybars4 vulnerabilities allowing code injection were publicly disclosed, detailing the exploit method.
github.com

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Common questions

Which versions are affected?
Pybars3 versions up to 0.9.7 and Pybars4 versions up to 0.9.13 are affected.
Is there a patch available?
Currently, no patches have been released for Pybars3, and Pybars4 remains vulnerable.
What should I do if I use these libraries?
Assess your usage of Pybars3 and Pybars4, and consider alternative libraries or implement strict input validation.