CVE-2021-29492 Information

Description

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.

CVSS Vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:L

Reference

https://github.com/envoyproxy/envoy/security/advisories/GHSA-4987-27fx-x6cf

Attack Complexity

LOW

Privileges Required

NONE

User Interaction Required

NONE

Scope

NONE

Confidentiality Impact

CHANGED

Integrity Impact

LOW

Availability Impact

LOW

Base Score

LOW

Base Severity

8.3