CVE-2026-90057 in Linux
Summary
by MITRE • 09/17/2026
In the Linux kernel, the following vulnerability has been resolved:
slip: remove slip_hangup() to fix use-after-free in slip_receive_buf()
Jaeyoung Chung and Eulgyu Kim reported a slab-use-after-free read in slip_receive_buf() when racing against tty hangup.
tty_ldisc_hangup() calls ld->ops->hangup() while holding only a read lock on tty->ldisc_sem (via tty_ldisc_ref()). Because slip_hangup() simply called slip_close(), it ran concurrently with reader functions such as slip_receive_buf().
slip_close() unregisters and frees the net device and its private struct slip, causing concurrent reader threads in slip_receive_buf() to dereference freed memory.
Line discipline close() is already guaranteed to be called under the write lock of tty->ldisc_sem during hangup processing (in tty_ldisc_reinit() or tty_ldisc_kill()).
Remove slip_hangup() so teardown is serialized cleanly by slip_close().
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Analysis
by VulDB Data Team • 09/17/2026
The Linux kernel contains a critical concurrency flaw within the Serial Line Internet Protocol driver, specifically affecting the interaction between terminal line discipline hangups and data reception routines. This vulnerability manifests as a slab-use-after-free condition in the slip_receive_buf function when it races against tty hangup operations. The root cause lies in an improper locking mechanism during the teardown phase of the network device associated with the serial line interface. When a user space process closes or resets the terminal, the kernel initiates a hangup sequence that invokes the line discipline's hangup callback. In this specific implementation, the slip_hangup function was designed to call slip_close, which is responsible for unregistering and freeing the network device structure along with its private data structures. However, the invocation of slip_hangup occurred while holding only a read lock on the tty->ldisc_sem semaphore via tty_ldisc_ref. This insufficient locking allowed concurrent execution paths to proceed simultaneously, creating a race condition where reader threads could still be actively processing incoming serial data in slip_receive_buf at the exact moment that slip_close was freeing the underlying memory structures.
The operational impact of this vulnerability is severe, as it allows for arbitrary code execution or system crashes through use-after-free exploitation. When slip_hangup triggers the deallocation of the net device and its private struct slip, any concurrent invocation of slip_receive_buf will attempt to dereference pointers that have already been returned to the slab allocator. This leads to undefined behavior, potentially resulting in kernel panics due to invalid memory access or, more dangerously, enabling an attacker with local user privileges to exploit the freed memory region. By overwriting the freed data before it is reallocated for another purpose, a malicious actor could hijack control flow within the kernel space. The vulnerability highlights a fundamental misunderstanding of synchronization primitives in the tty layer, where read locks were incorrectly used to protect operations that modify shared state and trigger resource deallocation, violating the principle that write-heavy or destructive operations must be serialized with exclusive access rights.
From a standards perspective, this flaw aligns closely with CWE-416, Use After Free, which describes situations where software continues to use memory after it has been freed, leading to unexpected behavior. Furthermore, in the context of attack patterns and detection methodologies, this vulnerability relates to ATT&CK technique T1059, Command and Scripting Interpreter, as an attacker could leverage such a kernel-level privilege escalation or denial-of-service condition to maintain persistence or disrupt services. The specific mechanism involves exploiting race conditions during resource cleanup, which is often categorized under CWE-362, Concurrent Execution using Shared Resource with Improper Synchronization. The failure to properly serialize the teardown process against active data processing threads represents a classic synchronization error that undermines the integrity of kernel memory management subsystems.
The resolution implemented by the Linux kernel maintainers involves removing the slip_hangup function entirely and ensuring that all teardown operations are serialized through slip_close under appropriate locking mechanisms. It is already guaranteed within the tty layer architecture that line discipline close callbacks, such as those invoked during hangup processing in functions like tty_ldisc_reinit or tty_ldisc_kill, must be executed while holding the write lock on tty->ldisc_sem. By eliminating the intermediate slip_hangup step and relying directly on the properly synchronized slip_close routine, the kernel ensures that no reader threads can access the network device structures after they have been marked for deallocation. This change enforces strict mutual exclusion between the hangup sequence and data reception paths, thereby preventing the race condition entirely. System administrators should ensure their kernels are updated to include this patch to mitigate the risk of local privilege escalation or denial-of-service attacks stemming from this concurrency flaw in serial line protocol handling.