CVE-2021-29492

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.

CvssV3 impact

BaseSeverity

CRITICAL

ConfidentialityImpact

HIGH

AttackComplexity

LOW

Scope

UNCHANGED

AttackVector

NETWORK

AvailabilityImpact

HIGH

IntegrityImpact

HIGH

PrivilegesRequired

NONE

BaseScore

9.8

VectorString

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

Version

3.1

UserInteraction

NONE

CvssV2 impact

AccessComplexity

LOW

ConfidentialityImpact

PARTIAL

AvailabilityImpact

PARTIAL

IntegrityImpact

PARTIAL

BaseScore

7.5

VectorString

AV:N/AC:L/Au:N/C:P/I:P/A:P

Version

2.0

AccessVector

NETWORK

Authentication

NONE