### Impact
– Attacker providing malicious redirect uri can cause DoS to oauthlib’s web application.
– Attacker can also leverage usage of `uri_validate` functions depending where it is used.

_What kind of vulnerability is it? Who is impacted?_
Oauthlib applications using OAuth2.0 provider support or use directly `uri_validate` function.

### Patches
_Has the problem been patched? What versions should users upgrade to?_
Issue fixed in 3.2.1 release.

### Workarounds
_Is there a way for users to fix or remediate the vulnerability without upgrading?_
The `redirect_uri` can be verified in web toolkit (i.e `bottle-oauthlib`, `django-oauth-toolkit`, …) before oauthlib is called. A sample check if `:` is present to reject the request can prevent the DoS, assuming no port or IPv6 is fundamentally required.

### References
Attack Vector:
– Attacker providing malicious redirect uri:
https://github.com/oauthlib/oauthlib/blob/d4bafd9f1d0eba3766e933b1ac598cbbf37b8914/oauthlib/oauth2/rfc6749/grant_types/base.py#L232
– Vulnerable `uri_validate` functions:
https://github.com/oauthlib/oauthlib/blob/2b8a44855a51ad5a5b0c348a08c2564a2e197ea2/oauthlib/uri_validate.py

### PoC
“`python
is_absolute_uri(“https://[:::::::::::::::::::::::::::::::::::::::]/path”)
“`

### Acknowledgement
Special thanks to Sebastian Chnelik – PyUp.ioRead More