CVE-2023-27491 Explained : Impact and Mitigation

This CVE record addresses the vulnerability "Envoy forwards invalid Http2/Http3 downstream headers" in the Envoy proxy software.

Understanding CVE-2023-27491

This vulnerability affects Envoy, an open-source edge and service proxy designed for cloud-native applications. It pertains to improper handling of downstream headers, potentially leading to security policy bypass in affected versions.

What is CVE-2023-27491?

Envoy, prior to versions 1.26.0, 1.25.3, 1.24.4, 1.23.6, and 1.22.9, could allow malformed requests from non-compliant HTTP/1 services. This could result in a security policy bypass, as compliant HTTP/1 services should reject malformed request lines.

The Impact of CVE-2023-27491

The vulnerability could be exploited to bypass security policies, potentially compromising the integrity and confidentiality of the affected systems. The base severity is rated as MEDIUM with a CVSS v3.1 base score of 5.4.

Technical Details of CVE-2023-27491

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

Vulnerability Description

The vulnerability lies in how Envoy handles downstream headers in HTTP/2 and HTTP/3 protocols, allowing for the potential forwarding of invalid headers.

Affected Systems and Versions

Affected Vendor: envoyproxy
Affected Product: envoy
Vulnerable Versions:
= 1.25.0, < 1.25.3

= 1.24.0, < 1.24.4

= 1.23.0, < 1.23.6

< 1.22.9

Exploitation Mechanism

The vulnerability could be exploited by sending specially crafted invalid HTTP/2 or HTTP/3 downstream headers to the affected versions of the Envoy proxy software.

Mitigation and Prevention

To address CVE-2023-27491 and enhance system security, immediate steps, long-term security practices, and patching recommendations are crucial.

Immediate Steps to Take

Update Envoy software to the patched versions (1.26.0, 1.25.3, 1.24.4, 1.23.6, 1.22.9) to mitigate the vulnerability.
Monitor and restrict network access to potentially vulnerable services.
Implement strict input validation mechanisms to detect and block malformed requests.

Long-Term Security Practices

Regularly update and patch software to address security vulnerabilities promptly.
Conduct security assessments and audits to identify and remediate potential weaknesses in the system.

Patching and Updates

It is recommended to apply the latest patches provided by Envoyproxy to ensure the security of systems using the Envoy proxy software. Regularly check for updates and security advisories from the vendor to stay protected against known vulnerabilities.