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.

How to fix CVE-2021-29492

To remediate CVE-2021-29492, upgrade the affected package to a fixed version below.

• —upgrade to 1.15.5 or later

Is CVE-2021-29492 being exploited?

Moderate — EPSS is 10.5%. Track this CVE but it's not at the top of the prioritisation list.

Affected packages (1)

• from 0, < 1.15.5, >= 1.16.0, < 1.16.4, >= 1.17.0, < 1.17.3, >= 1.18.0, < 1.18.3

CVSS scores

References (2)

• WEBgithub.com/envoyproxy/envoy/security/advisories/GHSA-4987-27fx-x6cf
• WEBnvd.nist.gov/vuln/detail/CVE-2021-29492