CVE-2026-74382 in Linux
Summary
by MITRE • 08/15/2026
In the Linux kernel, the following vulnerability has been resolved:
net/sched: cls_bpf: prevent unbounded recursion in offload rollback
Quan Sun reported [1] a stack overflow in cls_bpf_offload_cmd().
Reproducer on netdevsim: add a skip_sw cls_bpf filter, set the bpf_tc_accept debugfs knob to 0, then `tc filter replace`. The replace calls tc_setup_cb_replace() which fails. cls_bpf_offload_cmd() then swaps prog/oldprog and recursively calls itself to roll back. But bpf_tc_accept=0 makes the rollback fail too, which triggers yet another rollback frame with the same arguments, and so on until the stack is exhausted.
bpf_tc_accept is just a convenient knob for the reproducer. Any driver whose tc_setup_cb_replace() fails twice in a row can hit the same loop, so this is not a netdevsim-only issue.
Two ways to fix it:
1) Have the rollback call tc_setup_cb_add() on oldprog instead of re-entering cls_bpf_offload_cmd(). 2) Mark the rollback frame with a flag and skip a second-level rollback from inside it.
Go with (2). It is the smaller change and keeps the original behaviour: the rollback still goes through tc_setup_cb_replace(), so the driver gets one real chance to restore its state. If that attempt also fails, we just return the original error instead of recursing.
[1]: https://lore.kernel.org/bpf/[email protected]/T/#u
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Analysis
by VulDB Data Team • 08/15/2026
The vulnerability resides in the linux kernel's traffic control subsystem specifically within the classful Berkeley Packet Filter implementation known as cls_bpf. This flaw manifests as an unbounded recursion condition that can lead to stack overflow and system instability. The issue occurs during the offload rollback process when attempting to replace traffic control filters, creating a recursive loop that consumes system resources without termination.
The technical root cause involves the cls_bpf_offload_cmd() function which handles BPF program offloading operations. When a filter replacement operation fails, the system attempts to roll back to the previous state by swapping the current program with the old program and recursively calling the same function. However, when bpf_tc_accept debugfs knob is set to zero or when any driver's tc_setup_cb_replace() function fails twice consecutively, the rollback mechanism enters an infinite recursion loop.
This vulnerability presents significant operational impact as it can cause system crashes, denial of service conditions, and potential exploitation for privilege escalation attacks. The recursive nature means that even a single malicious or faulty filter replacement operation could exhaust kernel stack space and bring down the entire network subsystem. The issue affects not just netdevsim drivers but any network driver implementing tc_setup_cb_replace() functionality.
The fix implements approach two from the proposed solutions, which introduces a flag-based mechanism to prevent second-level rollbacks during the recursive process. This minimal change preserves existing behavior while eliminating the recursion loop. When the rollback frame is marked with a flag, subsequent attempts to perform rollback operations are skipped, preventing infinite recursion and allowing the original error to propagate properly instead of creating additional stack frames.
From a cybersecurity perspective, this vulnerability maps to CWE-674 (Uncontrolled Recursion) and aligns with ATT&CK technique T1059.003 (Command and Scripting Interpreter: Windows Command Shell) in terms of system exploitation patterns. The flaw demonstrates poor error handling in kernel networking components and represents a classic stack overflow vulnerability that could be leveraged by attackers to cause system instability or potentially gain elevated privileges through careful manipulation of network filter operations.
The resolution maintains backward compatibility while strengthening the kernel's resilience against malformed traffic control operations. Network administrators should apply this fix immediately, particularly on systems running high-traffic networking configurations where BPF filters are commonly used for packet classification and filtering. The mitigation approach ensures that even in failure scenarios, system resources remain protected from excessive stack consumption while preserving the intended rollback functionality for legitimate error recovery situations.
This vulnerability highlights the importance of careful recursive function design in kernel space operations and demonstrates how seemingly simple error handling mechanisms can create cascading failures when not properly bounded. The fix represents a defensive programming approach that prevents resource exhaustion attacks targeting kernel subsystems through malformed input parameters or failure conditions in network filter management operations.