CVE-2026-76403: Splunk Connect for Kafka Disclosure Flaw

CVE-2026-76403 Overview

CVE-2026-76403 affects Splunk Connect for Kafka versions below 2.2.7. The connector fails to apply configured certificate validation options when it builds the Hypertext Transfer Protocol (HTTP) client for the Kerberos authentication path. An unauthenticated attacker positioned in the network path can read or alter data sent from the connector to the Splunk HTTP Event Collector (HEC) in Splunk Enterprise. The flaw maps to Improper Certificate Validation [CWE-295] and enables man-in-the-middle (MITM) attacks against telemetry pipelines using Kerberos authentication.

Critical Impact
A network-positioned attacker can intercept or modify Kafka-to-Splunk event traffic, breaking confidentiality and integrity of ingested security and operational data.

Affected Products

Splunk Connect for Kafka versions below 2.2.7
Deployments using Kerberos authentication with the Splunk HTTP Event Collector
Splunk Enterprise environments receiving data from vulnerable connector versions

Discovery Timeline

2026-08-19 - CVE-2026-76403 published to the National Vulnerability Database (NVD)
2026-08-20 - Last updated in NVD database

Technical Details for CVE-2026-76403

Vulnerability Analysis

Splunk Connect for Kafka forwards events from Apache Kafka topics into Splunk Enterprise through the HTTP Event Collector. When operators configure Kerberos authentication for the outbound HEC connection, the connector constructs a new HTTP client dedicated to that authentication flow. This code path does not read or apply the certificate validation options defined in the connector configuration.

Because the resulting client skips proper Transport Layer Security (TLS) trust validation, it accepts arbitrary or attacker-controlled certificates. An attacker with network positioning between the Kafka connector and the HEC endpoint can present a rogue certificate, terminate the TLS session, and act as an active MITM. This exposes the full stream of events, including security-sensitive log data, to reading and tampering before it reaches the Splunk indexer.

Root Cause

The root cause is Improper Certificate Validation [CWE-295] in the Kerberos authentication code path. The HTTP client builder does not propagate the connector's TLS trust store, hostname verification, or certificate pinning settings. Non-Kerberos paths apply these controls, but the Kerberos branch bypasses them entirely, creating an inconsistent trust model within the same product.

Attack Vector

Exploitation requires a network-adjacent position between the Kafka connector host and the Splunk HEC endpoint, such as a compromised upstream router, ARP spoofing on a shared segment, or DNS manipulation. The attacker terminates TLS with a self-signed or unrelated certificate that the connector accepts without validation. Once positioned, the attacker can silently record every event forwarded by the connector or inject fabricated events into the Splunk index, corrupting downstream detections and audit records.

No verified public exploit code is available. See the Splunk Security Advisory SVD-2026-0808 for vendor technical details.

Detection Methods for CVE-2026-76403

Indicators of Compromise

Unexpected TLS certificates presented on the HEC endpoint that do not match the issued Splunk server certificate.
Gaps, duplicates, or anomalous event counts in Splunk indexes fed by Kafka Connect pipelines.
HEC ingestion traffic traversing unexpected intermediate hosts, proxies, or IP ranges.

Detection Strategies

Inventory all Splunk Connect for Kafka deployments and flag any instance running a version below 2.2.7 with Kerberos authentication enabled.
Compare TLS certificate fingerprints observed on the wire against the known-good HEC server certificate fingerprint.
Correlate Kafka connector send counts against Splunk HEC receive counts to identify silent drops or injections.

Monitoring Recommendations

Enable full TLS session logging on network sensors covering the Kafka-to-HEC path and alert on certificate changes.
Monitor for new ARP, DNS, or BGP anomalies on network segments carrying connector traffic.
Track configuration changes to kafka-connect-splunk connector properties, especially TLS and Kerberos settings.

How to Mitigate CVE-2026-76403

Immediate Actions Required

Upgrade Splunk Connect for Kafka to version 2.2.7 or later on all connector nodes.
Rotate any HEC tokens that traversed a vulnerable connector using Kerberos authentication.
Review recent Splunk ingest for anomalous or missing events that may indicate tampering.

Patch Information

Splunk has released a fixed version in Splunk Connect for Kafka 2.2.7, which applies the configured certificate validation options within the Kerberos authentication HTTP client. Refer to Splunk Security Advisory SVD-2026-0808 for official remediation guidance and version details.

Workarounds

Disable Kerberos authentication for the HEC output and use a non-Kerberos authentication path that correctly enforces TLS validation until patching is complete.
Restrict network paths between connector hosts and HEC endpoints using segmentation, IPsec, or mutual TLS enforced at a network appliance.
Deploy strict egress controls on connector hosts so that HEC traffic can only reach the intended Splunk indexer IP and port.

bash

# Verify the installed Splunk Connect for Kafka version
grep -i version /opt/kafka/connectors/splunk-kafka-connect/manifest.json

# Example connector properties to review for TLS enforcement
# splunk.hec.ssl.validate.certs=true
# splunk.hec.uri=https://hec.example.internal:8088