CVE-2021-29492 Bypass of path matching rules using escaped slash characters
Attackers can bypass URL-based access controls in Envoy by using escaped slashes, potentially gaining unauthorized access to protected backend resources.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2021-29492?
CVE-2021-29492 is a high-severity path traversal vulnerability in Envoyproxy Envoy, published on 28 May 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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.
Weakness: CWE-22
Which versions are affected by CVE-2021-29492?
1 open source package ship an affected version, including envoy. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
envoy Bitnami | All versions | 1.15.5, 1.16.4, 1.17.3, 1.18.3 |
Products include Envoyproxy Envoy.
How do I fix CVE-2021-29492?
Upgrade envoy to a fixed version for your release line: 1.15.5, 1.16.4, 1.17.3 or 1.18.3.
Upgrade, and resolve every user-supplied path against an allowed base folder before opening it. More about Path traversal.
Is CVE-2021-29492 being exploited?
There is no known exploitation of CVE-2021-29492 in the wild and no public exploit code.
Other vulnerabilities in Envoyproxy Envoy
Sources
Also known as BIT-envoy-2021-29492, GHSA-4987-27fx-x6cf.