CVE-2021-29492: Bypass of path matching rules using escaped slash characters
First published: Fri May 28 2021(Updated: )
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.
Credit: security-advisories@github.com
| Affected Software | Affected Version | How to fix |
|---|---|---|
| Envoy Proxy | <1.15.5 | |
| Envoy Proxy | >=1.16.0<1.16.4 | |
| Envoy Proxy | >=1.17.0<1.17.3 | |
| Envoy Proxy | >=1.18.0<1.18.3 |
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Frequently Asked Questions
What is CVE-2021-29492?
CVE-2021-29492 is a vulnerability in Envoy proxy that allows an attacker to bypass access control by crafting a path with escaped slashes in HTTP URL paths.
What is the severity of CVE-2021-29492?
The severity of CVE-2021-29492 is high, with a CVSS score of 8.3.
How does CVE-2021-29492 impact Envoy proxy?
CVE-2021-29492 impacts Envoy proxy versions 1.18.2 and before, allowing a remote attacker to bypass access control.
How can an attacker exploit CVE-2021-29492?
An attacker can exploit CVE-2021-29492 by crafting a path with escaped slashes, such as '/something%2F..%2Fadmin', to bypass access control.
Is there a fix available for CVE-2021-29492?
Yes, a fix is available for CVE-2021-29492. Users should update to Envoy proxy version 1.18.3 or later.
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