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In Splunk Connect for Kafka versions prior to 2.2.7, an unauthenticated attacker with network access to the Kafka Connect REST API can manipulate responses from an HTTP Event Collector (HEC) endpoint in Splunk Enterprise. This manipulation forces the connector into an infinite retry loop for failed event batches, ultimately halting all event delivery. The root cause is an unbounded default retry limit for failed HEC batches—the connector retries indefinitely instead of stopping after a finite number of attempts.
The attack chain begins when the adversary reaches the Kafka Connect REST API, which is typically exposed for administrative functions. By influencing the responses from a configured HEC endpoint—perhaps by causing deliberate failures or spoofing error signals—the attacker triggers the connector’s retry mechanism. Because the retry logic lacks a cap, each failed batch spawns a new retry attempt, consuming connector threads and resources. Over time, the backlog of pending retries exhausts the connector’s capacity, preventing new events from being processed and causing a denial-of-service condition.
This vulnerability is classified under CWE-400: Uncontrolled Resource Consumption. It requires the attacker to have network connectivity to both the Kafka Connect REST API and the HEC endpoint, but does not require authentication. The attack complexity is high because the adversary must influence HEC responses in a specific way. There is no impact on confidentiality or integrity—only availability is affected. The CVSS base score is 5.9 (Medium). Splunk addressed this issue in version 2.2.7 by implementing a finite retry limit.
DailyCVE Form:
Platform: Splunk Connect for Kafka
Version: below 2.2.7
Vulnerability: Unbounded retry loop
Severity: Medium (5.9)
date: 2026-08-19
Prediction: Patch already released (2.2.7)
What Undercode Say:
The vulnerability stems from a missing upper bound on retry attempts for failed HEC batches. Attackers can trigger this by influencing HEC responses, causing the connector to retry indefinitely. This is a classic resource exhaustion flaw (CWE-400). The fix in version 2.2.7 introduces a finite retry limit, breaking the infinite loop. Administrators should upgrade immediately or restrict REST API access to trusted hosts.
Check current Splunk Connect for Kafka version ./bin/splunk list app-versions | grep -i "splunk-connect-for-kafka" Verify Kafka Connect REST API exposure netstat -tulpn | grep 8083 Test HEC endpoint responsiveness curl -k https://<splunk-hec-host>:8088/services/collector/event -H "Authorization: Splunk <token>"
Exploit: (Educational Purposes!)
An attacker could:
- Identify a reachable Kafka Connect REST API (default port 8083)
- Locate a configured HEC endpoint in Splunk Enterprise
- Send malformed or delayed responses from the HEC to trigger failures
- Observe the connector entering an infinite retry loop for failed batches
- Continue until connector threads are exhausted and event delivery stops
Protection:
- Upgrade to Splunk Connect for Kafka version 2.2.7 or later
- Restrict Kafka Connect REST API access to trusted administrative hosts and networks
- Enforce secure HEC endpoint configurations with proper authentication
- Monitor connector logs for excessive retry attempts
- Implement network segmentation to limit exposure of the REST API
Impact:
- Availability: Complete denial of service for event delivery through the affected connector
- Confidentiality: None
- Integrity: None
- Attack Vector: Network-accessible, unauthenticated
- Complexity: High—requires ability to influence HEC responses
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Sources:
Reported By: nvd.nist.gov
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