CVE-2026-98113 in Linux
Summary
by MITRE • 09/25/2026
In the Linux kernel, the following vulnerability has been resolved:
ksmbd: rate limit unmapped SID errors
A client can include many structurally valid but unmapped SIDs in a DACL. Logging every mapping failure lets one request generate hundreds of kernel error messages.
Rate limit the message to prevent an authenticated client from flooding the kernel log.
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Analysis
by VulDB Data Team • 09/25/2026
The vulnerability identified within the Linux kernel's ksmbd component relates to insufficient rate limiting for security-related logging events, specifically concerning unmapped Security Identifiers (SIDs) in Discretionary Access Control Lists DACLs. This issue falls under the category of CWE-778 Insufficient Logging which can lead to information exposure or denial of service through log flooding when combined with excessive verbosity. The ksmbd module provides server support for SMB3 and earlier protocols allowing Linux systems to act as file servers compatible with Windows clients a critical infrastructure component in many enterprise environments where interoperability between operating systems is required.
When an authenticated client submits a request containing DACLs populated with numerous structurally valid but unmapped SIDs the kernel attempts to resolve each SID into a corresponding user or group identity for access control evaluation. Each resolution failure triggers a logging event intended to aid administrators in diagnosing permission issues however without rate limiting these events accumulate rapidly resulting in hundreds of error messages per single request this behavior creates an opportunity for denial of service attacks where malicious actors exploit the verbose logging mechanism to overwhelm system resources including disk I/O memory allocation and CPU cycles dedicated to log processing.
The operational impact of this vulnerability extends beyond mere performance degradation flooding the kernel log can obscure critical security events making incident response more difficult by burying genuine alerts among noise from legitimate but misconfigured clients or malicious probes additionally excessive logging consumes significant storage space potentially filling up disk partitions which may cause system instability or prevent further logging entirely thereby reducing visibility into actual security incidents. Furthermore in high-throughput environments the cumulative effect of such log generation can degrade overall network performance and increase latency for all connected clients affecting service availability and reliability.
Mitigation strategies primarily involve applying the upstream kernel patch that implements rate limiting mechanisms to constrain the frequency of unmapped SID error messages this ensures that only a manageable number of warnings are generated per unit time preventing resource exhaustion while still retaining visibility into persistent configuration errors administrators should also review their ksmbd configurations to ensure appropriate logging levels are set and consider implementing log rotation policies alongside monitoring solutions capable of detecting anomalous spikes in log volume which could indicate ongoing exploitation attempts. Regularly updating the kernel to include this fix is essential for maintaining a secure posture especially in environments where external clients frequently interact with SMB shares requiring strict adherence to access control best practices such as minimizing reliance on unmapped or legacy SIDs within DACLs and validating client-side permission structures before deployment.