CVE-2021-29492 : Vulnerability Insights and Analysis

This article provides detailed insights into CVE-2021-29492, a vulnerability in Envoy that allows attackers to bypass access control rules using escaped slash characters.

Understanding CVE-2021-29492

CVE-2021-29492 is a security vulnerability in Envoy proxy versions 1.18.2 and earlier that enables attackers to escalate privileges by manipulating URL paths.

What is CVE-2021-29492?

Envoy, a cloud-native service proxy, fails to decode escaped slash sequences in HTTP URL paths, allowing attackers to bypass access controls.

The Impact of CVE-2021-29492

The vulnerability poses a high risk as attackers can exploit it for privilege escalation when using RBAC or JWT filters based on URL paths.

Technical Details of CVE-2021-29492

This section delves into the specifics of the vulnerability, including the affected systems, exploitation mechanism, and mitigation strategies.

Vulnerability Description

Envoy's inability to decode escaped slash characters in URL paths could lead to unauthorized access beyond established policies.

Affected Systems and Versions

Envoy versions up to 1.18.2 are affected by this vulnerability, impacting users with back end servers interpreting slash sequences interchangeably.

Exploitation Mechanism

Attackers can exploit this flaw by crafting URL paths with escaped slash characters, delivering them via untrusted clients to circumvent access controls.

Mitigation and Prevention

To safeguard systems from CVE-2021-29492, immediate steps, long-term security practices, and the importance of patching and updates are crucial.

Immediate Steps to Take

Implement the patches released in versions 1.18.3, 1.17.3, 1.16.4, and 1.15.5 to enable path normalization and decode escaped slash characters.

Long-Term Security Practices

Reconfigure back end servers not to treat

%2F

and

%5C

interchangeably if relying on URL path-based access control to prevent unauthorized access.

Patching and Updates

Regularly apply updates and patches provided by Envoy to mitigate the risks associated with CVE-2021-29492.