CVE-2023-25165: Helm Information Disclosure Vulnerability

CVE-2023-25165 Overview

CVE-2023-25165 is an information disclosure vulnerability in Helm, the popular package manager for Kubernetes applications. The vulnerability exists in the getHostByName template function, which was introduced in Helm v3. This function accepts a hostname and performs a DNS lookup to return the corresponding IP address. The security issue arises because information passed into the chart can be disclosed to DNS servers during the lookup process, potentially exposing sensitive configuration data to unauthorized parties.

Critical Impact
Malicious Helm charts can leverage the getHostByName function to exfiltrate sensitive values and configuration data to attacker-controlled DNS servers during chart rendering operations.

Affected Products

Helm versions prior to 3.11.1
Helm SDK implementations that render charts using vulnerable versions
Kubernetes deployments utilizing affected Helm versions

Discovery Timeline

2023-02-08 - CVE-2023-25165 published to NVD
2024-11-21 - Last updated in NVD database

Technical Details for CVE-2023-25165

Vulnerability Analysis

This vulnerability is classified as an Information Exposure issue (CWE-200). The getHostByName template function in Helm performs DNS lookups when charts are rendered using helm install, helm upgrade, or helm template commands. The core security problem is that any data passed to this function as a hostname parameter will be transmitted to DNS servers as part of the DNS query, creating an unintended data exfiltration channel.

The vulnerability is particularly concerning in scenarios where Helm charts from untrusted sources are processed, as a malicious chart author could craft templates that embed sensitive values (such as secrets, credentials, or configuration data) into the hostname parameter. When the chart is rendered, this sensitive information would be sent to DNS servers controlled by the attacker.

Root Cause

The root cause of this vulnerability lies in the design of the getHostByName function, which directly uses user-controlled input as DNS query parameters without adequate consideration for the information disclosure implications. The function was designed for legitimate use cases of resolving hostnames during chart templating but lacked safeguards against malicious abuse where sensitive chart values could be encoded into DNS queries.

Attack Vector

The attack requires an adversary to create or modify a Helm chart that uses the getHostByName function with sensitive values as input parameters. When an unsuspecting user renders this chart using Helm commands or the Helm SDK, the sensitive information is transmitted via DNS queries. The attacker can capture this data by monitoring DNS traffic to their controlled DNS servers. This is a network-based attack that requires low privileges (the user must have permission to render Helm charts) and no user interaction beyond normal chart operations.

The exploitation mechanism works by embedding sensitive template values into DNS lookups. For example, a malicious chart could concatenate secret values with an attacker-controlled domain, causing the secrets to appear in DNS query logs when the chart is processed.

Detection Methods for CVE-2023-25165

Indicators of Compromise

Unusual DNS queries containing encoded data or secrets in hostnames
DNS traffic to unexpected or suspicious external domains during Helm operations
Chart templates containing getHostByName function calls with dynamic values
Abnormal outbound DNS activity during helm install, helm upgrade, or helm template operations

Detection Strategies

Audit all Helm charts for usage of the getHostByName function before deployment
Implement DNS monitoring to detect queries with suspicious hostname patterns during Helm operations
Review third-party and community Helm charts for potential malicious template functions
Deploy network security tools to monitor and log DNS queries originating from Kubernetes infrastructure

Monitoring Recommendations

Enable logging for all Helm operations in your CI/CD pipelines and production environments
Configure DNS query logging on internal DNS servers to detect data exfiltration attempts
Implement network segmentation to restrict DNS traffic from Helm-related workloads
Set up alerts for DNS queries containing unusually long hostnames or encoded data patterns

How to Mitigate CVE-2023-25165

Immediate Actions Required

Upgrade Helm to version 3.11.1 or later immediately
Audit all existing Helm charts in your environment for getHostByName function usage
Review and validate any third-party or community charts before deployment
Implement chart validation policies in your CI/CD pipelines to detect usage of the vulnerable function

Patch Information

The Helm project has addressed this vulnerability in version 3.11.1. The fix is available in the GitHub commit 5abcf74227bfe8e5a3dbf105fe62e7b12deb58d2. Users should upgrade to Helm 3.11.1 or later to receive the security fix. Additional details about the vulnerability and remediation are available in the GitHub Security Advisory GHSA-pwcw-6f5g-gxf8.

Workarounds

Manually review all Helm chart templates for getHostByName function usage before rendering
Implement network policies to restrict DNS traffic during Helm operations
Use chart validation tools to scan for potentially dangerous template functions
Consider blocking untrusted charts from being deployed until they can be audited

bash

# Verify Helm version and upgrade if necessary
helm version
# Expected: version.BuildInfo{Version:"v3.11.1"} or higher

# Search for getHostByName usage in chart templates
grep -r "getHostByName" ./charts/

# Upgrade Helm to patched version
# For Linux/macOS using script
curl https://raw.githubusercontent.com/helm/helm/main/scripts/get-helm-3 | bash