{"id":"BIT-envoy-2021-29492","summary":"Bypass of path matching rules using escaped slash characters","details":"Envoy is a cloud-native edge/middle/service proxy. 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 in versions 1.18.3, 1.17.3, 1.16.4, 1.15.5 contain new path normalization option to decode escaped slash characters. As a workaround, if back end servers treat `%2F` and `/` and `%5C` and `\\` interchangeably and a URL path based access control is configured, one may reconfigure the back end server to not treat `%2F` and `/` and `%5C` and `\\` interchangeably.","aliases":["CVE-2021-29492","GHSA-4987-27fx-x6cf"],"modified":"2026-09-08T08:47:22.070302721Z","published":"2024-03-06T10:58:39.469Z","database_specific":{"cpes":["cpe:2.3:a:envoyproxy:envoy:*:*:*:*:*:*:*:*"],"severity":"High"},"references":[{"type":"ADVISORY","url":"https://github.com/envoyproxy/envoy/security/advisories/GHSA-4987-27fx-x6cf"},{"type":"WEB","url":"https://nvd.nist.gov/vuln/detail/CVE-2021-29492"}],"affected":[{"package":{"name":"envoy","ecosystem":"Bitnami","purl":"pkg:bitnami/envoy"},"ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"1.15.5"},{"introduced":"1.16.0"},{"fixed":"1.16.4"},{"introduced":"1.17.0"},{"fixed":"1.17.3"},{"introduced":"1.18.0"},{"fixed":"1.18.3"}]}],"database_specific":{"source":"https://github.com/bitnami/vulndb/tree/main/data/envoy/BIT-envoy-2021-29492.json"},"severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:L"}]}],"schema_version":"1.9.0"}