CVE-2023-41039

Format string allows information disclosure in RestrictedPython

• CVSS 7.7
• CWE-74 Improper Neutralization of Special Elements in Output Used by a Downstream Component ('Injection')
• Information Leakage
• Remote

RestrictedPython is a restricted execution environment for Python to run untrusted code. Python's "format" functionality allows someone controlling the format string to "read" all objects accessible through recursive attribute lookup and subscription from objects he can access. This can lead to critical information disclosure. With `RestrictedPython`, the format functionality is available via the `format` and `format_map` methods of `str` (and `unicode`) (accessed either via the class or its instances) and via `string.Formatter`. All known versions of `RestrictedPython` are vulnerable. This issue has been addressed in commit `4134aedcff1` which has been included in the 5.4 and 6.2 releases. Users are advised to upgrade. There are no known workarounds for this vulnerability.

CVE

CVE-2023-41039

CWE

CWE-74 Improper Neutralization of Special Elements in Output Used by a Downstream Component ('Injection')

CVSS base score

7.7

Published

2023-08-30

OWASP

A05 Security Misconfiguration

Orthogonal defect classification

Function

Code defect classification

Incorrect Functionality

Category

Information Leakage

Subcategory

Information Disclosure

Accessibility scope

Remote

Impact

Information Disclosure

Fixed by upgrading

Yes

Solution

Update to RestrictedPython version 5.4 or 6.2 or higher.

def format_string(format_string, user):
    return format_string.format(user=user)

user_data = {'name': 'Alice', 'secret': 'This is a secret!'}
format_string = "Hello, {user.name}. Your secret is: {user.secret}"
result = format_string(format_string, user_data)
print(result)

def format_string(format_string, user):
    allowed_fields = {
        'name': user.get('name')
    }
    return format_string.format(user=allowed_fields)

user_data = {'name': 'Alice', 'secret': 'This is a secret!'}
format_string_input = "Hello, {user[name]}."
result = format_string(format_string_input, user_data)
print(result)

@misc{vaitp:cve202341039,
  title        = {{Format string allows information disclosure in RestrictedPython}},
  author       = {Bogaerts, Fr\'ed\'eric and Ivaki, Naghmeh and Fonseca, Jos\'e},
  year         = {2023},
  note         = {VAITP Python Vulnerability Dataset, entry CVE-2023-41039},
  howpublished = {\url{https://netpack.pt/vaitp/vulnerability/CVE-2023-41039/}}
}