CVE-2026-68143 in Linux
Summary
by MITRE • 08/10/2026
In the Linux kernel, the following vulnerability has been resolved:
net: slip: serialize receive against buffer reallocation
sl_realloc_bufs() replaces rbuff and updates buffsize while holding sl->lock. slip_receive_buf() reads those fields and writes through rbuff without holding the lock.
An MTU change can therefore race with receive processing. An MTU shrink can expose the new smaller rbuff with the old larger bound, causing an out-of-bounds write. A receive callback which already loaded the old rbuff can instead continue writing after that buffer has been freed.
Serialize receive processing with sl_realloc_bufs() by holding sl->lock while consuming each receive batch.
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Analysis
by VulDB Data Team • 08/10/2026
The vulnerability resides within the Linux kernel's slip network driver implementation, specifically addressing a race condition between buffer reallocation and receive processing operations. This issue manifests in the interaction between two critical functions: sl_realloc_bufs() which handles buffer resizing and slip_receive_buf() which processes incoming data packets. The core problem emerges from improper synchronization mechanisms where sl_realloc_bufs() modifies shared buffer pointers and size parameters while holding a lock, yet slip_receive_buf() accesses these same variables without maintaining the necessary locking protocol during its execution phase.
The technical flaw creates a fundamental race condition scenario where concurrent operations can lead to memory corruption and potential system instability. When the MTU (Maximum Transmission Unit) changes during active network processing, the buffer reallocation process can overwrite existing buffer references while receive operations are still in progress. This occurs because the function sl_realloc_bufs() updates the rbuff pointer and buffsize variables while holding the sl->lock, but slip_receive_buf() reads these values and performs writes to rbuff without acquiring the same lock protection. The consequence of this design flaw allows for out-of-bounds memory writes when an MTU shrink operation occurs, as the new smaller buffer may be referenced by code that was previously operating on a larger buffer with corresponding bounds checks.
The operational impact of this vulnerability extends beyond simple data corruption, potentially enabling privilege escalation and system instability. An attacker could exploit this race condition to cause arbitrary code execution within kernel space by manipulating network traffic patterns to trigger the specific timing window where buffer reallocation occurs concurrently with packet reception. The vulnerability affects systems utilizing the slip (Serial Line IP) network driver implementation, which is commonly found in embedded systems and specialized networking applications where serial line communication is required. This flaw directly violates security principles outlined in the CWE-362 category for concurrent execution issues, specifically addressing the improper synchronization of shared resources during critical operations.
The mitigation strategy requires implementing proper locking mechanisms throughout the receive processing pipeline to ensure atomicity between buffer reallocation and data consumption phases. The solution involves holding the sl->lock continuously while processing each receive batch, preventing any interleaving between buffer modification and consumption operations. This approach aligns with established security practices from the ATT&CK framework's defense evasion techniques, specifically addressing the need for proper resource management and synchronization in kernel-level code. The fix ensures that all buffer access operations maintain consistency regardless of concurrent modification attempts, thereby preventing the out-of-bounds write conditions that could lead to privilege escalation or system compromise. This remediation addresses fundamental security weaknesses in kernel memory management and reinforces proper concurrency control mechanisms essential for maintaining system integrity in network driver implementations.