CVE-2017-9461 in Samba
Summary
by MITRE
smbd in Samba before 4.4.10 and 4.5.x before 4.5.6 has a denial of service vulnerablity (fd_open_atomic infinite loop with high CPU usage and memory consumption) due to wrongly handling dangling symlinks.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 12/08/2022
The vulnerability identified as CVE-2017-9461 affects the smbd service within Samba software versions prior to 4.4.10 and 4.5.x versions before 4.5.6. This issue represents a denial of service condition that can be exploited to consume excessive system resources and potentially render the affected service unavailable to legitimate users. The vulnerability specifically manifests when the smbd daemon processes file operations involving dangling symbolic links, creating a scenario where the system enters an infinite loop that consumes substantial CPU cycles and memory resources.
The technical root cause of this vulnerability lies in the improper handling of dangling symbolic links within the fd_open_atomic function of the Samba file server implementation. When smbd encounters a symbolic link that points to a non-existent target file or directory, the system fails to properly validate or handle this condition, leading to a recursive or iterative process that never terminates. This flaw enables an attacker to craft specific file operations that trigger the problematic code path, causing the daemon to enter an infinite loop where it continuously processes the same symbolic link without making progress. The resulting resource exhaustion manifests as sustained high CPU utilization and memory consumption, effectively creating a denial of service condition that can impact the availability of file sharing services.
The operational impact of this vulnerability extends beyond simple service disruption to potentially affect broader network infrastructure and business operations. Organizations relying on Samba-based file sharing services may experience complete unavailability of their file servers, impacting file access for multiple users and applications simultaneously. The resource consumption characteristics make this vulnerability particularly dangerous in environments where system resources are already constrained or where multiple concurrent attacks can compound the denial of service effects. Network administrators may observe unusual system performance degradation, increased system load, and potential cascading failures if the affected service is critical to other applications or if the system lacks proper resource monitoring and protection mechanisms.
Mitigation strategies for CVE-2017-9461 primarily focus on applying the vendor-provided security patches and updates that address the specific handling of dangling symbolic links within the Samba smbd service. Organizations should immediately upgrade to Samba versions 4.4.10 or 4.5.6 and later, which contain the necessary fixes to properly handle this edge case in symbolic link processing. Additionally, implementing proper input validation and sanitization measures can help reduce the attack surface, though this approach is less effective than applying the official patches. Network segmentation and access control measures can provide additional defense in depth, limiting the potential impact of exploitation attempts. Security monitoring should include detection of unusual CPU and memory consumption patterns that may indicate exploitation attempts, with alerts configured for sustained resource utilization above normal thresholds.
This vulnerability aligns with CWE-400, which describes the weakness of "Uncontrolled Resource Consumption," and represents a classic example of how improper error handling can lead to denial of service conditions. The ATT&CK framework categorizes this vulnerability under the "Resource Exhaustion" technique, where adversaries consume system resources to prevent legitimate use of services. The vulnerability demonstrates how seemingly minor implementation flaws in system components can have significant operational impacts, particularly when these components handle user-provided input or operate in multi-user environments where malicious actors may attempt to exploit such weaknesses for disruption purposes. Organizations should maintain regular patch management processes and security monitoring to identify and remediate similar vulnerabilities before they can be exploited in operational environments.