CVE-2026-76288 in Splunk
Summary
by MITRE • 10/22/2026
In Splunk Enterprise versions below 10.4.4, 10.2.8, 10.0.11, and 9.4.16, an unauthenticated user could send a single crafted request to the Splunk Web JavaScript logger endpoint and cause Splunk Web to stop responding to requests. Splunk Web remains unavailable until Splunk Enterprise is restarted. The vulnerability is possible because Splunk Web does not limit request-header parsing before processing the request.
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Analysis
by VulDB Data Team • 10/22/2026
The identified vulnerability in Splunk Enterprise versions prior to 10.4.4, 10.2.8, 10.0.11, and 9.4.16 represents a critical availability risk stemming from insufficient input validation within the web application layer. Specifically, the flaw resides in the handling of HTTP request headers by the Splunk Web JavaScript logger endpoint. An unauthenticated attacker can exploit this weakness by transmitting a single, specially crafted HTTP request that triggers an abnormal condition during header parsing. Because the system fails to enforce limits on the size or complexity of these headers before processing them, it leads to resource exhaustion or internal errors that cause the Splunk Web service to cease responding to all incoming requests. This state persists until the entire Splunk Enterprise instance is manually restarted by a system administrator, resulting in significant operational downtime and loss of access to security monitoring capabilities during the recovery period.
From a technical perspective, this vulnerability aligns with CWE-20 Improper Input Validation, as the application does not adequately sanitize or constrain incoming data structures before they are processed by internal components. The specific mechanism involves the failure to limit request-header parsing, which is a common vector for denial-of-service attacks in web applications that rely on dynamic header processing without strict bounds checking. By allowing excessively large or malformed headers, the server consumes excessive memory or CPU resources during the parsing phase, leading to a crash of the web service process. This behavior is consistent with patterns observed in various HTTP-based denial-of-service vulnerabilities where resource limits are not enforced at the ingress point of the application server.
The operational impact of this vulnerability is severe due to its unauthenticated nature and high availability implications. Since no authentication credentials are required, any external actor on the network can trigger the service outage without prior access or privilege escalation. The consequence is a complete denial of service for Splunk Web, which serves as the primary interface for security analysts and administrators to view logs, create alerts, and manage configurations. During the period where Splunk Web is unresponsive until a restart occurs, organizations lose visibility into their IT infrastructure, hindering incident response efforts and potentially masking ongoing attacks that would otherwise be detected by the SIEM platform. This creates a window of opportunity for adversaries who may exploit the distraction or lack of monitoring to perform further malicious activities undetected.
In terms of threat modeling, this vulnerability can be mapped to MITRE ATT&CK technique T1499 Endpoint Denial of Service, specifically under sub-techniques related to resource exhaustion via application layer attacks. The attack vector is classified as Network-based with no user interaction required beyond sending the crafted packet, placing it in the initial access or impact phase depending on whether the organization considers service disruption an immediate impact event. Security teams should prioritize this vulnerability due to its ease of exploitation and direct impact on business continuity.
Mitigation strategies focus primarily on applying vendor-provided patches immediately upon availability for all affected versions listed above. Organizations running Splunk Enterprise below version 10.4.4, 10.2.8, 10.0.11, or 9.4.16 must upgrade to the latest stable release where this header parsing limitation has been addressed. In environments where immediate patching is not feasible due to operational constraints, temporary mitigations should be implemented at the network perimeter level. This includes configuring web application firewalls or reverse proxies to enforce strict limits on HTTP request header size and complexity. By dropping requests that exceed defined thresholds for header length or number of headers, organizations can prevent the malformed packets from reaching the vulnerable Splunk Web service, thereby maintaining availability while preparing for a permanent software update.