{"action":"opened","issue":{"url":"https://api.github.com/repos/matrix-org/synapse/issues/4242","repository_url":"https://api.github.com/repos/matrix-org/synapse","labels_url":"https://api.github.com/repos/matrix-org/synapse/issues/4242/labels{/name}","comments_url":"https://api.github.com/repos/matrix-org/synapse/issues/4242/comments","events_url":"https://api.github.com/repos/matrix-org/synapse/issues/4242/events","html_url":"https://github.com/matrix-org/synapse/issues/4242","id":386170537,"node_id":"MDU6SXNzdWUzODYxNzA1Mzc=","number":4242,"title":"URL preview IP blacklist doesn't work on IPv6 and isn't bulletproof","user":{"login":"hawkowl","id":3307100,"node_id":"MDQ6VXNlcjMzMDcxMDA=","avatar_url":"https://avatars0.githubusercontent.com/u/3307100?v=4","gravatar_id":"","url":"https://api.github.com/users/hawkowl","html_url":"https://github.com/hawkowl","followers_url":"https://api.github.com/users/hawkowl/followers","following_url":"https://api.github.com/users/hawkowl/following{/other_user}","gists_url":"https://api.github.com/users/hawkowl/gists{/gist_id}","starred_url":"https://api.github.com/users/hawkowl/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/hawkowl/subscriptions","organizations_url":"https://api.github.com/users/hawkowl/orgs","repos_url":"https://api.github.com/users/hawkowl/repos","events_url":"https://api.github.com/users/hawkowl/events{/privacy}","received_events_url":"https://api.github.com/users/hawkowl/received_events","type":"User","site_admin":false},"labels":[{"id":481619152,"node_id":"MDU6TGFiZWw0ODE2MTkxNTI=","url":"https://api.github.com/repos/matrix-org/synapse/labels/security","name":"security","color":"b60205","default":false}],"state":"open","locked":false,"assignee":null,"assignees":[],"milestone":null,"comments":0,"created_at":"2018-11-30T12:36:54Z","updated_at":"2018-11-30T12:36:54Z","closed_at":null,"author_association":"CONTRIBUTOR","body":"We need to have another look at this, especially after https://github.com/matrix-org/synapse/pull/4215 , which changes where the IP blacklist check is done, and is potentially vulnerable to an attack where a super low TTL or no DNS caching can have the check pass on a non whitelisted IP and then the request be made to a refetched DNS query which has a blacklisted IP."}}
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