CVE-2021-27918 : Security Advisory and Response

A vulnerability in encoding/xml in Go before version 1.15.9 and 1.16.x before 1.16.1 can lead to an infinite loop under specific conditions. This could be exploited by an attacker to cause a denial of service (DoS) condition.

Understanding CVE-2021-27918

This CVE refers to a flaw in the encoding/xml package of Go programming language versions prior to 1.15.9 and 1.16.1. The issue arises when a custom TokenReader returns EOF in the middle of an element, triggering an infinite loop in certain decoder methods.

What is CVE-2021-27918?

CVE-2021-27918 involves a DoS vulnerability in the Go programming language's encoding/xml package. Attackers can exploit this flaw by manipulating a custom TokenReader to induce an infinite loop when encountering EOF within an XML element during decoding.

The Impact of CVE-2021-27918

The impact of this vulnerability is the potential for a DoS condition, where an attacker could repeatedly trigger the infinite loop, consuming excessive resources and rendering the affected service unresponsive. This could lead to service disruption and availability issues.

Technical Details of CVE-2021-27918

This section outlines the specific technical aspects of the CVE, including the vulnerability description, affected systems, and exploitation mechanism.

Vulnerability Description

The vulnerability in encoding/xml could result in an infinite loop if a custom TokenReader encounters EOF within an XML element when used with certain decoder methods, such as Decode, DecodeElement, or Skip.

Affected Systems and Versions

Systems running Go programming language versions before 1.15.9 and 1.16.1 are vulnerable to CVE-2021-27918 when utilizing the encoding/xml package. It is crucial for users of these versions to apply the necessary patches.

Exploitation Mechanism

To exploit this vulnerability, an attacker would need to craft XML input that triggers the specific conditions causing the infinite loop. By sending malicious XML payloads that lead to premature EOF signals, they could disrupt the decoding process and impact service availability.

Mitigation and Prevention

Protecting systems against CVE-2021-27918 involves immediate actions and long-term security practices to minimize the risk of exploitation.

Immediate Steps to Take

Users are advised to update their Go programming language installations to version 1.15.9 or 1.16.1, which contain patches addressing the infinite loop issue in encoding/xml. It is crucial to apply these updates promptly to mitigate the vulnerability.

Long-Term Security Practices

Incorporating secure coding practices, performing regular code reviews, and staying informed about software security updates are essential long-term strategies to enhance overall system security and resilience.

Patching and Updates

Regularly monitoring for security advisories from Go and related vendors, such as Gentoo, and promptly applying patches and updates can help safeguard systems against known vulnerabilities like CVE-2021-27918.