A security regression of CVE-2019-9636 was discovered in python since commit d537ab0ff9767ef024f26246899728f0116b1ec3 affecting versions 2.7, 3.5, 3.6, 3.7 and from v3.8.0a4 through v3.8.0b1, which still allows an attacker to exploit CVE-2019-9636 by abusing the user and password parts of a URL. When an application parses user-supplied URLs to store cookies, authentication credentials, or other kind of information, it is possible for an attacker to provide specially crafted URLs to make the application locate host-related information (e.g. cookies, authentication data) and send them to a different host than where it should, unlike if the URLs had been correctly parsed. The result of an attack may vary based on the application.
Weakness
The product does not properly encode or decode the data, resulting in unexpected values.
Affected Software
| Name |
Vendor |
Start Version |
End Version |
| Python |
Python |
2.7.0 (including) |
2.7.17 (excluding) |
| Python |
Python |
3.5.0 (including) |
3.5.8 (excluding) |
| Python |
Python |
3.6.0 (including) |
3.6.9 (excluding) |
| Python |
Python |
3.7.0 (including) |
3.7.4 (excluding) |
| Python |
Python |
3.8.0-alpha4 (including) |
3.8.0-alpha4 (including) |
| Python |
Python |
3.8.0-beta1 (including) |
3.8.0-beta1 (including) |
Potential Mitigations
- Assume all input is malicious. Use an “accept known good” input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does.
- When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, “boat” may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as “red” or “blue.”
- Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code’s environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.
References