CVE-2019-15226 Explained : Impact and Mitigation

Envoy, upon receipt of every incoming request header data, goes through the existing request headers to ensure that the combined size of the headers remains within a prescribed limit. However, in versions 1.10.0 through 1.11.1 for HTTP/1.x traffic, as well as all versions of Envoy for HTTP/2 traffic, the implementation had performance characteristics of O(n^2). This means that a malicious attacker could potentially create a request that remains under the maximum request header size but contains numerous small headers, ultimately leading to excessive CPU consumption and resulting in a denial-of-service attack.

Understanding CVE-2019-15226

This CVE involves a vulnerability in Envoy that could be exploited by a remote attacker to launch a denial-of-service attack by crafting a specific type of request.

What is CVE-2019-15226?

CVE-2019-15226 is a vulnerability in Envoy that allows an attacker to consume excessive CPU resources by sending a specially crafted request with numerous small headers, potentially leading to a denial-of-service condition.

The Impact of CVE-2019-15226

The impact of this vulnerability is the potential for a denial-of-service attack, causing excessive CPU consumption and disrupting the normal operation of the affected system.

Technical Details of CVE-2019-15226

This section provides more technical insights into the vulnerability.

Vulnerability Description

Upon receiving each incoming request header data, Envoy will iterate over existing request headers to verify that the total size of the headers stays below a maximum limit. The implementation in affected versions had O(n^2) performance characteristics, allowing attackers to exploit this behavior.

Affected Systems and Versions

Versions 1.10.0 through 1.11.1 for HTTP/1.x traffic
All versions of Envoy for HTTP/2 traffic

Exploitation Mechanism

A remote attacker can craft a request that stays below the maximum request header size but consists of many thousands of small headers to consume CPU and result in a denial-of-service attack.

Mitigation and Prevention

To address CVE-2019-15226, the following steps can be taken:

Immediate Steps to Take

Update Envoy to a patched version that addresses the vulnerability.
Monitor system resources for any unusual spikes in CPU consumption.

Long-Term Security Practices

Implement network-level protections to mitigate denial-of-service attacks.
Regularly update and patch software to prevent known vulnerabilities.

Patching and Updates

Ensure that Envoy is regularly updated to the latest version to mitigate the risk of exploitation.