CVE-2026-42316: Azure Kusto Kafka Connector Privilege Escalation

CVE-2026-42316 Overview

CVE-2026-42316 is a Kusto Query Language (KQL) injection vulnerability in the kafka-sink-azure-kusto Kafka Connect plugin, the official Microsoft sink connector for Azure Data Explorer. Versions prior to 5.2.3 fail to sanitize user-controlled values inside the kusto.tables.topics.mapping configuration. An actor with permission to submit or edit Kafka Connect connector configurations can embed KQL metacharacters to execute arbitrary management commands against the target Azure Data Explorer database. The flaw is categorized under CWE-943: Improper Neutralization of Special Elements in Data Query Logic.

Critical Impact

An attacker with privileged access to connector configuration can execute arbitrary KQL management commands in the context of the connector's service principal, enabling schema enumeration, ingestion-mapping tampering, and modification of streaming or retention policies.

Affected Products

• kafka-sink-azure-kusto Kafka Connect plugin versions prior to 5.2.3
• Azure Data Explorer (Kusto) databases targeted by vulnerable connector deployments
• Kafka Connect environments hosting the affected sink connector

Discovery Timeline

• 2026-05-11 - CVE-2026-42316 published to NVD
• 2026-05-13 - Last updated in NVD database

Technical Details for CVE-2026-42316

Vulnerability Analysis

The kafka-sink-azure-kusto connector constructs KQL management and query commands by directly interpolating configuration values into command templates using Java's String.formatted(...). The db, table, mapping, and format fields of each mapping entry in the kusto.tables.topics.mapping configuration are concatenated into KQL strings without sanitization or parameterization.

For example, FETCH_TABLE_COMMAND.formatted(table) produces <table> | count, and FETCH_TABLE_MAPPING_COMMAND.formatted(table, format, mapping) produces .show table <table> ingestion <format> mapping '<mapping>'. An attacker who supplies crafted values containing KQL metacharacters such as ;, |, or ' can break out of the intended command boundary and append arbitrary commands.

Exploitation is limited to actors with privileged access to the Kafka Connect REST API or connector configuration storage. No end-user interaction or Kafka record payload is involved, which classifies this as a tampering vulnerability rather than a remote unauthenticated attack.

Root Cause

The root cause is the absence of input neutralization on configuration-supplied identifiers before they enter KQL command strings. The connector trusts configuration values implicitly and treats them as safe identifiers rather than untrusted input requiring escaping or validation against an allowlist.

Attack Vector

An attacker with the ability to submit or edit Kafka Connect connector configurations injects KQL metacharacters into the db, table, mapping, or format fields. When the connector loads the configuration and issues management commands to Azure Data Explorer, the injected payload executes under the connector's service principal. This grants the attacker the effective KQL privileges held by that principal on the target database.

The vulnerability manifests in the command formatting logic of the connector. Refer to the GitHub Security Advisory GHSA-c9mr-mqvh-6wgj and the fix in Pull Request #155 for code-level technical details.

Detection Methods for CVE-2026-42316

Indicators of Compromise

• Kafka Connect connector configurations containing KQL metacharacters (;, |, ') in the db, table, mapping, or format fields of kusto.tables.topics.mapping
• Unexpected .show, .alter, .drop, or .set management commands in Azure Data Explorer audit logs originating from the connector's service principal
• Modifications to ingestion mappings, streaming policies, or retention policies that do not correspond to authorized change requests

Detection Strategies

• Audit existing Kafka Connect connector configurations for unusual characters in mapping fields and compare against a known-good baseline
• Enable and review Azure Data Explorer diagnostic logs (SucceededIngestion, FailedIngestion, Command) for management commands issued by Kafka Connect service principals
• Correlate connector configuration change events from the Kafka Connect REST API with subsequent ADX command activity

Monitoring Recommendations

• Forward Kafka Connect REST API access logs and Azure Data Explorer command logs to a centralized SIEM for cross-source correlation
• Alert on any KQL control commands (.alter, .drop, .set-or-append) executed by service principals associated with sink connectors
• Monitor changes to kusto.tables.topics.mapping configuration values and require review for entries containing punctuation outside expected identifier character sets

How to Mitigate CVE-2026-42316

Immediate Actions Required

• Upgrade kafka-sink-azure-kusto to version 5.2.3 or later across all Kafka Connect workers
• Restrict access to the Kafka Connect REST API and configuration storage to a minimal set of trusted operators
• Apply least-privilege permissions to the Azure Data Explorer service principal used by the connector, limiting it to required database, table, and ingestion roles
• Review historical connector configurations and ADX command logs for evidence of injected KQL metacharacters

Patch Information

The vulnerability is fixed in kafka-sink-azure-kusto version 5.2.3. The patch sanitizes configuration-supplied identifiers before they are interpolated into KQL commands. See the GitHub Release v5.2.3 and the merged Pull Request #155 for details.

Workarounds

• Where immediate upgrade is not possible, enforce strict allowlist validation on connector configuration submissions, rejecting any db, table, mapping, or format value containing characters outside [A-Za-z0-9_]
• Reduce the Azure Data Explorer permissions of the connector service principal to the minimum required for ingestion, removing rights to alter schemas, mappings, or policies
• Require code review and change-control approval for all Kafka Connect connector configuration changes referencing Azure Data Explorer targets

# Verify installed connector version on a Kafka Connect worker
curl -s http://kafka-connect:8083/connector-plugins | \
  jq '.[] | select(.class | contains("KustoSinkConnector"))'

# Example allowlist validation (reject configs with KQL metacharacters)
CONFIG_VALUE="my_table"
if [[ ! "$CONFIG_VALUE" =~ ^[A-Za-z0-9_]+$ ]]; then
  echo "Rejected: configuration value contains disallowed characters"
  exit 1
fi