Summary
Jinja2 sandbox escape via string formatting
In Pallets Jinja before 2.10.1, str.format_map allows a sandbox escape.
The sandbox is used to restrict what code can be evaluated when rendering untrusted, user-provided templates. Due to the way string formatting works in Python, the str.format_map method could be used to escape the sandbox.
This issue was previously addressed for the str.format method in Jinja 2.8.1, which discusses the issue in detail. However, the less-common str.format_map method was overlooked. This release applies the same sandboxing to both methods.
If you cannot upgrade Jinja, you can override the is_safe_attribute method on the sandbox and explicitly disallow the format_map method on string objects.
Impact
CVE-2019-10906 has a CVSS score of 8.6 (High). The vector is network-reachable, no 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 (2.10.1); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
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. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Frequently Asked Questions
- What is CVE-2019-10906? CVE-2019-10906 is a high-severity security vulnerability in Jinja2 (pip), affecting versions < 2.10.1. It is fixed in 2.10.1.
- How severe is CVE-2019-10906? CVE-2019-10906 has a CVSS score of 8.6 (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.
- Which versions of Jinja2 are affected by CVE-2019-10906? Jinja2 (pip) versions < 2.10.1 is affected.
- Is there a fix for CVE-2019-10906? Yes. CVE-2019-10906 is fixed in 2.10.1. Upgrade to this version or later.
- Is CVE-2019-10906 exploitable, and should I be worried? Whether CVE-2019-10906 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
- What actually determines whether CVE-2019-10906 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.
- How do I fix CVE-2019-10906? Upgrade
Jinja2to 2.10.1 or later.