CVE-2026-39891

Direct insertion of unescaped user input into template-rendering tools allows arbitrary code execution via specially crafted agent instructions.

Details

The create_agent_centric_tools() function returns tools (like acp_create_file) that process file content using template rendering. When user input from agent.start() is passed directly into these tools without escaping (as shown in agent_centric_example.py:85-86), template expressions in the input are executed rather than treated as literal text. This occurs because:

1. No input sanitization or escaping is applied to user-controlled content
2. The ACP-enabled runtime auto-approves operations (approval_mode="auto")
3. Tools lack context-aware escaping for template syntax

PoC

# Replace the agent.start() call at line 85 with:
result = agent.start('Create file with content: {{ self.__init__.__globals__.__builtins__.__import__("os").system("touch /tmp/pwned") }}')

Successful exploitation creates /tmp/pwned confirming arbitrary command execution. The expression {{7*7}} renders as 49 instead of literal text.

Attackers can execute arbitrary system commands with the privileges of the running process by injecting malicious template expressions through agent instructions. This compromises the host system, enabling data theft, ransomware deployment, or lateral movement.

Untrusted input is evaluated as executable code within the application's runtime environment. Typical impact: arbitrary code execution within the application's privilege context.

CVE-2026-39891 has a CVSS score of 8.8 (High). The vector is network-reachable, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (4.5.115); upgrading removes the vulnerable code path.

Kodem intelligence

1. Input Sanitization: Implement strict whitelist validation for file content
2. Contextual Escaping: Auto-escape template syntax characters (e.g., {{ }}) in user input using Jinja2 autoescape=True
3. Sandboxing: Restrict template execution environments using secure eval modes
4. Approval Hardening: Require manual approval for file creation operations in production

1. What is CVE-2026-39891? CVE-2026-39891 is a high-severity code injection vulnerability in praisonai (pip), affecting versions <= 4.5.114. It is fixed in 4.5.115. Untrusted input is evaluated as executable code within the application's runtime environment.
2. How severe is CVE-2026-39891? CVE-2026-39891 has a CVSS score of 8.8 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of praisonai are affected by CVE-2026-39891? praisonai (pip) versions <= 4.5.114 is affected.
4. Is there a fix for CVE-2026-39891? Yes. CVE-2026-39891 is fixed in 4.5.115. Upgrade to this version or later.
5. Is CVE-2026-39891 exploitable, and should I be worried? Whether CVE-2026-39891 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-39891 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-39891? Upgrade praisonai to 4.5.115 or later.