CVE-2026-31563
Published: 24 April 2026
Summary
CVE-2026-31563 is a high-severity an unspecified weakness vulnerability in Linux Linux Kernel. Its CVSS base score is 7.5 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Application or System Exploitation (T1499.004); ranked at the 22.8th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified are NIST 800-53 SI-2 (Flaw Remediation) and SC-5 (Denial-of-service Protection).
Deeper analysis
CVE-2026-31563 is a vulnerability in the Linux kernel's macb (Media Access Controller block) network driver. Following commit 6bc8a5098bf4 ("net: macb: Fix tx_ptr_lock locking"), the driver frees transmit (TX) socket kernel buffers (SKBs) using napi_consume_skb() while interrupts (IRQs) are disabled, violating the function's intended usage outside IRQ-disabled contexts. This triggers a kernel warning and call trace in softirq handling, as observed on hardware like ZynqMP ZCU102 during ksoftirqd execution.
The vulnerability has a CVSS v3.1 base score of 7.5 (AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H), indicating network-accessible exploitation with low complexity, no privileges or user interaction required, and high availability impact. Remote attackers can trigger it by generating network traffic that exercises the macb driver's TX path under the affected conditions, potentially leading to repeated kernel warnings and softirq disruptions that degrade system stability or cause denial of service.
Kernel stable patches address the issue by replacing napi_consume_skb() with dev_consume_skb_any(), which is safe for IRQ-disabled contexts. Relevant commits include 647b8a2fe474 (for certain stable branches), 78c8b090a3d5, 92e7081f0c79, 984350b37372, and ca4d05afb468, available via kernel.org stable repository. Security practitioners should update affected Linux kernels to versions incorporating these fixes.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-25456
Vulnerability details
In the Linux kernel, the following vulnerability has been resolved: net: macb: Use dev_consume_skb_any() to free TX SKBs The napi_consume_skb() function is not intended to be called in an IRQ disabled context. However, after commit 6bc8a5098bf4 ("net: macb: Fix tx_ptr_lock…
more
locking"), the freeing of TX SKBs is performed with IRQs disabled. To resolve the following call trace, use dev_consume_skb_any() for freeing TX SKBs: WARNING: kernel/softirq.c:430 at __local_bh_enable_ip+0x174/0x188, CPU#0: ksoftirqd/0/15 Modules linked in: CPU: 0 UID: 0 PID: 15 Comm: ksoftirqd/0 Not tainted 7.0.0-rc4-next-20260319-yocto-standard-dirty #37 PREEMPT Hardware name: ZynqMP ZCU102 Rev1.1 (DT) pstate: 200000c5 (nzCv daIF -PAN -UAO -TCO -DIT -SSBS BTYPE=--) pc : __local_bh_enable_ip+0x174/0x188 lr : local_bh_enable+0x24/0x38 sp : ffff800082b3bb10 x29: ffff800082b3bb10 x28: ffff0008031f3c00 x27: 000000000011ede0 x26: ffff000800a7ff00 x25: ffff800083937ce8 x24: 0000000000017a80 x23: ffff000803243a78 x22: 0000000000000040 x21: 0000000000000000 x20: ffff000800394c80 x19: 0000000000000200 x18: 0000000000000001 x17: 0000000000000001 x16: ffff000803240000 x15: 0000000000000000 x14: ffffffffffffffff x13: 0000000000000028 x12: ffff000800395650 x11: ffff8000821d1528 x10: ffff800081c2bc08 x9 : ffff800081c1e258 x8 : 0000000100000301 x7 : ffff8000810426ec x6 : 0000000000000000 x5 : 0000000000000001 x4 : 0000000000000001 x3 : 0000000000000000 x2 : 0000000000000008 x1 : 0000000000000200 x0 : ffff8000810428dc Call trace: __local_bh_enable_ip+0x174/0x188 (P) local_bh_enable+0x24/0x38 skb_attempt_defer_free+0x190/0x1d8 napi_consume_skb+0x58/0x108 macb_tx_poll+0x1a4/0x558 __napi_poll+0x50/0x198 net_rx_action+0x1f4/0x3d8 handle_softirqs+0x16c/0x560 run_ksoftirqd+0x44/0x80 smpboot_thread_fn+0x1d8/0x338 kthread+0x120/0x150 ret_from_fork+0x10/0x20 irq event stamp: 29751 hardirqs last enabled at (29750): [<ffff8000813be184>] _raw_spin_unlock_irqrestore+0x44/0x88 hardirqs last disabled at (29751): [<ffff8000813bdf60>] _raw_spin_lock_irqsave+0x38/0x98 softirqs last enabled at (29150): [<ffff8000800f1aec>] handle_softirqs+0x504/0x560 softirqs last disabled at (29153): [<ffff8000800f2fec>] run_ksoftirqd+0x44/0x80
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
The CVE describes a remotely triggerable kernel driver flaw in the macb TX path that produces softirq warnings and availability degradation; this directly maps to exploitation of a system component to achieve endpoint DoS.
CVEs Like This One
Affected Assets
Mitigating Controls
Mitigating Controls (NIST 800-53 r5) AI
Timely remediation through kernel patches (e.g., replacing napi_consume_skb() with dev_consume_skb_any()) directly eliminates the improper TX SKB freeing in IRQ-disabled contexts.
Requires secure error handling in kernel drivers to prevent availability impacts from misuse of functions like napi_consume_skb() in IRQ-disabled contexts.
Mitigates the high-impact DoS from repeated kernel warnings and softirq disruptions triggered by remote network traffic on the macb driver.