CVE-2026-104112 in nscd
Summary
by MITRE • 10/09/2026
A missing release of resources in the illumos name service cache daemon (nscd) allows a local user to exhaust kernel memory. The nscd door server procedure, switcher() in usr/src/cmd/nscd/nscd_frontend.c, does not close file descriptors that are passed with a door call but not used by the request, and the main nscd door at /var/run/name_service_door accepts passed descriptors from any user in its zone. Because nscd also runs with an unlimited file descriptor limit, an unprivileged local user, including one in a non-global zone, can repeatedly pass a descriptor to its zone's nscd in a door_call() loop, causing the file descriptor table of nscd to grow without bound in kernel memory. This causes a denial of service of nscd and can render processes in all zones on the host unresponsive. The flaw has existed since 2006 (illumos-gate commit cb5caa98), and affects any illumos distribution prior to illumos-gate commit af810a72.
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Analysis
by VulDB Data Team • 10/09/2026
The vulnerability identified involves a critical resource management failure within the name service cache daemon, known as nscd, in illumos-based operating systems. This flaw allows an unprivileged local user to exhaust kernel memory by exploiting how file descriptors are handled during inter-process communication via door calls. The core technical issue resides in the switcher function located in usr/src/cmd/nscd/nscd_frontend.c. When a client process invokes nscd through a door call, it may pass additional file descriptors along with the request payload. However, if these passed descriptors are not utilized by the specific service being requested, the daemon fails to close them properly. This oversight results in leaked file descriptor handles that remain open within the nscd process context indefinitely.
The operational impact of this flaw is severe due to the architecture of illumos zones and the configuration of nscd. The main door endpoint for name services, located at /var/run/name_service_door, accepts passed descriptors from any user within its zone without sufficient validation or cleanup procedures. Furthermore, nscd typically operates with an unlimited file descriptor limit to ensure it can handle high volumes of concurrent requests efficiently. An attacker, including those confined to a non-global zone, can exploit this by repeatedly invoking door_call in a tight loop while passing unused file descriptors each time. Each invocation increments the open file count for nscd without releasing them, causing the kernel memory footprint associated with these descriptor tables to grow continuously and without bound.
This uncontrolled growth of resource usage leads directly to a denial of service condition. As the number of leaked file descriptors increases, system resources are consumed until they are exhausted. This can cause nscd itself to become unresponsive or crash due to resource limits being reached at the kernel level. More critically, because name services are fundamental to many system operations across all zones on an illumos host, the failure of nscd can render processes in other zones unable to resolve names or perform essential network and identity lookups. This effectively compromises the availability of the entire multi-tenant environment, impacting not just the attacking user but potentially all users sharing the same physical hardware infrastructure.
From a classification perspective, this vulnerability aligns with CWE-772: Missing Release of Resource after Effective Lifetime. The failure to release file descriptors constitutes a classic resource leak that degrades system stability over time rather than causing immediate data corruption or privilege escalation. In terms of attack vectors and tactics, this flaw is relevant to ATT&CK techniques involving local exploitation for denial of service, specifically leveraging improper input handling in privileged services. Although the vulnerability has existed since 2006, originating from commit cb5caa98 in illumos-gate, it remains a significant risk for distributions that have not incorporated the fix introduced in commit af810a72.
Mitigation strategies primarily involve applying the specific patch associated with commit af810a72 or later versions of illumos where this leak has been addressed by ensuring passed file descriptors are closed if unused. For systems unable to update immediately, administrators should consider restricting access to /var/run/name_service_door through stricter zone permissions or ACLs, although this may impact legitimate functionality. Additionally, configuring nscd with a lower maximum open files limit can mitigate the severity of memory exhaustion, though it must be balanced against performance requirements for name resolution services. Regular auditing of file descriptor usage in critical daemons and implementing automated monitoring for abnormal growth in resource consumption are also recommended defensive measures to detect such leaks early before they lead to system-wide outages.