CVE-2026-99249 in Linux
Summary
by MITRE • 11/03/2026
In the Linux kernel, the following vulnerability has been resolved:
pid_namespace: make zap_pid_ns_processes() freezable
When the init of a pid namespace exits, zap_pid_ns_processes() waits until all other pids in the namespace are freed. A tracer outside the namespace that does not reap its traced zombies keeps those pids allocated, so this wait has no upper bound, and while it lasts every suspend attempt fails:
Freezing user space processes failed after 20.006 seconds (2 tasks refusing to freeze, wq_busy=0):
Neither wait is freezable. The first loop sleeps in do_wait(), which returns -ERESTARTSYS on the freezer's fake signal; the loop then clears TIF_SIGPENDING and waits again without ever freezing. The final loop sleeps in TASK_INTERRUPTIBLE, and since nothing clears TIF_SIGPENDING there, schedule() returns immediately after the first freeze attempt and the task spins until the wait ends.
Sleep in TASK_INTERRUPTIBLE | TASK_FREEZABLE in do_wait(), so that the freezer can freeze tasks waiting there directly, and in TASK_IDLE | TASK_FREEZABLE in the final loop, like coredump_task_exit() does.
This was hit with Chromium-based browsers: crashpad ptrace-attaches the threads of a crashed renderer, which is a pid namespace init, and does not reap those killed during the dump.
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Analysis
by VulDB Data Team • 11/03/2026
The Linux kernel contains a critical flaw within the process identifier namespace management logic that prevents system suspension when specific tracing conditions are met in user space applications. This vulnerability centers on the zap_pid_ns_processes function, which is responsible for cleaning up processes upon the exit of the init process within a pid namespace. Under normal circumstances, this function waits until all other processes in the namespace have been freed before completing its cleanup routine. However, if an external tracer attached to these processes fails to reap zombie children created during that period, those processes remain allocated indefinitely. Consequently, the wait condition inside zap_pid_ns_processes has no upper bound and never completes, effectively blocking any subsequent attempt by the operating system to suspend or hibernate.
The operational impact of this flaw is severe for systems relying on power management features such as sleep states. When a user attempts to freeze user space processes, the kernel encounters tasks that refuse to enter a frozen state due to their internal waiting loops. Specifically, one loop sleeps in do_wait and returns with an error code indicating it should restart upon receiving a signal from the freezer subsystem. Instead of freezing, this task clears its pending signal flag and waits again without ever entering a suspended state. A second loop within the same routine sleeps in an interruptible state but fails to clear the pending signal flag properly during freeze attempts. This causes schedule calls to return immediately after each freeze attempt, resulting in a tight spin that prevents the freezer from successfully suspending the task until the underlying wait condition resolves.
This issue was notably triggered by Chromium-based browsers utilizing crashpad for handling renderer crashes. When a renderer process within its own pid namespace crashes, crashpad uses ptrace to attach to and trace the threads of that crashed process. During this debugging session, if the browser does not reap the killed processes generated during the dump creation, those zombies persist in memory. Because these traced zombie tasks are held by an external tracer outside their native pid namespace, they prevent zap_pid_ns_processes from completing its cleanup. This blockage directly interferes with the kernel's ability to freeze user space processes, leading to timeouts and failed suspension attempts as observed in system logs reporting refused freezes after twenty seconds.
From a technical classification perspective, this vulnerability aligns with CWE-400 Uncontrolled Resource Consumption because the unbounded wait leads to resource holding that blocks critical system operations. It also relates to CWE-835 Loop Without Necessary Exit Condition regarding the logic within do_wait and the final cleanup loop where signal handling prevents proper state transitions. In terms of adversary behavior, this scenario reflects ATT&CK technique T1055 Process Injection via ptrace, as external tracing is used to attach to processes in a way that inadvertently creates a denial-of-service condition for system power management features rather than malicious exploitation.
Mitigation strategies should focus on ensuring proper reaping of traced zombie processes by applications utilizing ptrace attachments. Developers using crashpad or similar debugging tools must ensure that all child processes created during the tracing session are properly waited upon and cleaned up before detaching from the target process. On the kernel side, while patching is required to make these specific wait loops freezable by adjusting task states to include TASK_FREEZABLE flags, system administrators can temporarily mitigate the impact by avoiding suspension attempts while such debugging sessions are active or ensuring that browser crash handlers correctly reap all associated threads and processes immediately upon dump completion.