Sunday, May 30, 2021



### Description Envoy does not decode escaped slash sequences `%2F` and `%5C` in HTTP URL paths in versions 1.18.2 and before. A remote attacker may craft a path with escaped slashes, e.g. `/something%2F..%2Fadmin`, to bypass access control, e.g. a block on `/admin`. A backend server could then decode slash sequences and normalize path and provide an attacker access beyond the scope provided for by the access control policy. ### Impact Escalation of Privileges when using RBAC or JWT filters with enforcement based on URL path. Users with back end servers that interpret `%2F` and `/` and `%5C` and `\` interchangeably are impacted. ### Attack Vector URL paths containing escaped slash characters delivered by untrusted client. ### Patches Envoy versions 1.18.3, 1.17.3, 1.16.4, 1.15.5 contain new path normalization option to decode escaped slash characters. ### Workarounds If back end servers treat `%2F` and `/` and `%5C` and `\` interchangeably and a URL path based access control is configured, we recommend reconfiguring back end server to not treat `%2F` and `/` and `%5C` and `\` interchangeably if feasible. ### Credit Ruilin Yang ([email protected]) ### References ### For more information If you have any questions or comments about this advisory: * Open an issue in [Envoy repo]( * Email us at [envoy-security](mailto:[email protected])

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Thanks for everything Templateism - You should have written the code a little more complicated