CVE-2026-99085
UnknownSummary
A Linux kernel vulnerability was fixed in the sched_ext scheduler that caused a CPU hotplug hang when a dying CPU's tasks remained in the BPF scheduler. Such tasks were still counted on the runqueue, but an inactive CPU no longer called ops.dispatch() and could not pull them back, blocking the hotplug thread and cpu_down() while holding cpu_hotplug_lock. The fix re-enqueues tasks on the offline rq to the local DSQ so balance_push() can move them off.
Risk Assessment
An organization may experience a hang of CPU offlining or the entire system during hotplug operations, leading to service unavailability and forced restarts. In scenarios with tasks affine only to the dying CPU, offlining may stall until the watchdog intervenes.
Recommendation
Update the Linux kernel to a version containing the fix for CVE-2026-99085. Until patched, avoid routine CPU hotplug operations on systems using sched_ext with a BPF scheduler.
Other vulnerabilities in Linux kernel
See all- CVE-2026-99087Unknown
In the Linux kernel, dm-integrity has a NULL pointer dereference when a device with the SB_FLAG_DIRTY_BITMAP flag is activated in 'R' mode. The dm_integrity_resume function attempts to read the journal containing the bitmap, causing a crash. The fix skips writes to the device in 'R' mode during resume.
- CVE-2026-99086Unknown
In the Linux kernel, dm-integrity does not validate the superblock on resume, allowing a user to modify the superblock on the underlying device while the dm-integrity device is suspended. This can cause a mismatch in in-memory structure sizes and an out-of-bounds write past the journal, including a 512-byte write through a NULL pointer. The fix snapshots the validated superblock in the constructor and refuses to resume if the on-disk geometry changed.
- CVE-2026-99084Unknown
In the Linux kernel, a flaw was fixed in iterate_dir() where the directory's i_rwsem lock was held during readdir even for immutable directories that are never removed. For the nullfs instance directory (shared across mount namespaces and kernel threads), a malicious reader could hold the lock indefinitely, blocking mkdir, lookups, and mounts for other users. A new FOP_IMMUTABLE flag was added to skip the lock for such directories.
- CVE-2026-99083Unknown
In the Linux kernel, the ksmbd server has a heap out-of-bounds write in krb5_authenticate(). When SMB2_SESSION_SETUP is processed as a non-first element of a compounded SMB2 request, the out_len calculation omits work->next_smb2_rsp_hdr_off, overstating available buffer space and allowing memcpy() to write the AP-REP blob past response_buf. The fix subtracts this value when computing out_len.
- CVE-2026-99082Unknown
A bug was fixed in the Linux kernel KVM on x86 regarding the per-vCPU MMIO cache. The cache was tagged with a memslot generation, but both the fill and validation paths used kvm_memslots(), which unconditionally selects address space 0 even when the vCPU runs in SMM and uses address space 1. As a result, an SMM memslot update could leave an apparently valid entry from the old SMM address space after the vCPU returns to the normal address space, letting a guest force a KVM_EXIT_MMIO for valid RAM.
- CVE-2026-99080Unknown
In the Linux kernel, clear_inode() has an xarray node leak that can be triggered, among other ways, via madvise. Rather than fixing the leaks where they occur, the fix calls xa_destroy(), which has the side effect of cycling the i_pages lock.
- CVE-2026-99079Unknown
In the Linux kernel, the net/mlx5e driver can release a stale XSK buffer during refill retry on a legacy cyclic RQ. When refill succeeds only partially, a WQE left without a replacement retains its old buffer pointer, which may be allocated to another WQE, leading to freeing a live buffer and double-publishing the same UMEM frame. The fix marks the WQE as released immediately after the driver-side free.
- CVE-2026-99078Unknown
In the Linux kernel, the net/mlx5e driver can release a stale XSK buffer during MPWQE refill retry on a striding RQ. When XSK allocation returns -ENOMEM, actual_wq_head is not advanced and a later NAPI poll may call xsk_buff_free() again through stale pointers after frames return to the XSK pool. The fix sets all skip_release_bitmap bits in the error path of mlx5e_xsk_alloc_rx_mpwqe().
- CVE-2026-99077Unknown
A vulnerability in the Linux kernel's IPv4/UDP handling allowed off-path attackers to conduct a side-channel attack on the FIB nexthop exception (FNHE) cache. Previously, an exception was only created if the UDP packet could be matched to an existing socket, enabling discovery of the ephemeral port used by a connected UDP socket. The fix always creates a FNHE before attempting socket matching.
- CVE-2026-99076Unknown
A vulnerability in the Linux kernel's IPv6/UDP handling allowed off-path attackers to conduct a side-channel attack on the exception cache to discover the ephemeral port used by a connected UDP socket. Previously, an exception was only created if the UDP packet could be matched to an existing socket. The fix always creates an exception before attempting socket matching.
Original NVD description (English source)
In the Linux kernel, the following vulnerability has been resolved: sched_ext: Fix CPU hotplug hang when a dying CPU's tasks sit in the BPF scheduler A CPU going down has to empty its own rq. Its hotplug thread waits in sched_cpu_wait_empty() until nothing else is left, and the only thing that wakes it is balance_push(), which runs from __schedule() on the dying CPU and pushes off the migratable tasks the CPU picks. sched_ext breaks this. A task sitting on a user DSQ or held by the BPF scheduler is still counted on its rq, but an inactive CPU no longer calls ops.dispatch() and can't pull the task back. The dying CPU goes idle with the task still counted, and one of two things happens: - Another CPU consumes the task. The rq empties without a __schedule() on the dying CPU, so the hotplug thread is never woken and cpu_down() hangs holding cpu_hotplug_lock. - The task is affine only to the dying CPU. Nothing can move it, and the offline stalls until the watchdog ejects the BPF scheduler. When the rq goes offline, re-enqueue every task on it that isn't already on the local DSQ. An enqueue on an offline rq lands on the local DSQ, so the dying CPU itself picks the tasks and balance_push() pushes them off, the same as for the other sched classes. From then on no sched_ext path on another CPU can pull a task off the rq. ops.dispatch() currently stops as soon as the CPU goes inactive, and CPU hotplug then waits for an RCU grace period before taking the rq offline. A BPF-held task affine only to the dying CPU and preempted inside an RCU read-side critical section would block that grace period, and the rq would never go offline. Test SCX_RQ_ONLINE directly so that ops.dispatch() keeps running until the rq goes offline. Only the dying CPU's own hotplug thread clears the flag during teardown, and task_can_run_on_remote_rq() still keeps other rqs' tasks off the CPU.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS