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CVE-2026-13435

Improper input validation in Langflow's PythonREPL allows sandbox escape.

  • CVSS 9.9
  • 94
  • Input Validation and Sanitization
  • Remote

IBM Langflow OSS 1.0.0 through 1.10.1 contains an improper input validation vulnerability in the PythonREPL sandbox implementation.

CVE
CVE-2026-13435
CWE
94
CVSS base score
9.9
Published
2026-07-30
OWASP
A03 Injection
Orthogonal defect classification
Checking
Code defect classification
Incorrect Check
Category
Input Validation and Sanitization
Subcategory
Command Injection
Accessibility scope
Remote
Impact
Arbitrary Code Execution
Affected component
IBM Langflow
Fixed by upgrading
Yes

Solution

Upgrade to IBM Langflow OSS version 1.10.2.

Vulnerable code sample

import io
import sys


class PythonREPL:
    def __init__(self, globals=None, locals=None):
        self.globals = globals if globals is not None else {}
        self.locals = locals if locals is not None else {}

    def run(self, command: str) -> str:
        if "__" in command:
            return "Error: blacklisted token '__' in command."

        old_stdout = sys.stdout
        sys.stdout = captured_output = io.StringIO()
        try:
            # VULNERABLE: substring blacklist is not a sandbox; exec runs attacker code
            exec(command, self.globals, self.locals)
            output = captured_output.getvalue()
        except Exception as e:
            output = str(e)
        finally:
            sys.stdout = old_stdout
        return output

Patched code sample

import ast
import io
import sys


class PythonREPL:
    def __init__(self, globals=None, locals=None):
        self.globals = globals if globals is not None else {}
        self.locals = locals if locals is not None else {}

    def run(self, command: str) -> str:
        old_stdout = sys.stdout
        sys.stdout = captured_output = io.StringIO()
        try:
            # FIX: evaluate literals only; no exec/eval path remains for the input
            output = repr(ast.literal_eval(command))
        except (ValueError, SyntaxError, MemoryError, RecursionError) as e:
            output = f"Error: only literal expressions are allowed ({e})"
        finally:
            sys.stdout = old_stdout
        return output

Payload

__import__('os').system('id')

Cite this entry

@misc{vaitp:cve202613435,
  title        = {{Improper input validation in Langflow's PythonREPL allows sandbox escape.}},
  author       = {Bogaerts, Fr\'ed\'eric and Ivaki, Naghmeh and Fonseca, Jos\'e},
  year         = {2026},
  note         = {VAITP Python Vulnerability Dataset, entry CVE-2026-13435},
  howpublished = {\url{https://netpack.pt/vaitp/vulnerability/CVE-2026-13435/}}
}
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