CVE-2026-74626 Overview
CVE-2026-74626 is a resource exhaustion vulnerability in the Linux kernel's Non-Transparent Bridge (NTB) network device driver (ntb_netdev). The ntb_netdev_rx_handler() function passes each received socket buffer (skb) to the network stack before allocating a replacement. When allocation fails, no buffer is reposted to the receive queue. Each failure permanently removes one buffer from the RX ring while the interface stays up. Enough failures stall reception entirely, producing a persistent denial of service on the affected interface.
Critical Impact
Repeated skb allocation failures progressively drain the ntb_netdev RX queue, causing the network interface to stop receiving traffic until the driver is reloaded.
Affected Products
- Linux kernel ntb_netdev driver (Non-Transparent Bridge network device)
- Multiple stable branches referenced by upstream fix commits 18781cc0, 272df0f, 3f2a15f, 6d7f8a2, 755fd78, a4e3409, d2121fa, and fcaf8ba
- Systems using NTB interconnects for host-to-host networking (typical in PCIe fabric and storage appliances)
Discovery Timeline
- 2026-08-22 - CVE-2026-74626 published to NVD
- 2026-08-27 - Last updated in NVD database
Technical Details for CVE-2026-74626
Vulnerability Analysis
The ntb_netdev driver bridges the kernel networking stack to an NTB transport channel. Its receive path posts a fixed pool of skbs to the transport layer. When a frame arrives, ntb_netdev_rx_handler() runs and immediately delivers the completed skb upward. Only after handoff does the handler attempt to allocate a replacement skb and repost it to the queue.
This ordering creates a lossy dependency on memory availability. If netdev_alloc_skb() returns NULL under memory pressure, the handler cannot repost, and the RX ring loses one slot. The driver includes no deferred retry path, so the slot stays empty for the interface's lifetime. Each subsequent allocation failure shrinks the queue further until the transport has no buffers to fill, at which point reception halts completely.
The fix reverses the ordering: allocate the replacement skb first. On allocation failure, drop the current packet and repost the original skb, preserving queue depth so reception resumes once memory pressure eases.
Root Cause
The root cause is improper resource management on an error path. The handler releases a buffer before securing its replacement and provides no compensating refill mechanism when allocation fails, resulting in monotonic queue depletion under sustained memory pressure.
Attack Vector
The issue is network-reachable in the sense that traffic on the NTB interface drives the affected code path. An adversary or noisy neighbor able to induce kernel memory pressure while the interface is active can accelerate queue depletion. The impact is limited to availability of the NTB network interface; there is no confidentiality or integrity impact.
No verified public exploit code is available. Refer to the upstream commits linked below for the exact patch semantics.
Detection Methods for CVE-2026-74626
Indicators of Compromise
- Kernel log messages from ntb_netdev indicating dropped receives or allocation failures
- Steady decline in RX throughput on NTB interfaces that recovers only after driver reload or reboot
- Growth in rx_dropped counters reported by ip -s link show for the NTB netdev
Detection Strategies
- Monitor kernel ring buffer output (dmesg) for ntb_netdev warnings correlated with page allocation failure events
- Track per-interface RX queue depth and drop counters via ethtool statistics and node_exporter
- Alert on interfaces whose received-packet rate falls to zero while link state remains up
Monitoring Recommendations
- Baseline NTB interface throughput and set alerts on sustained drops below expected floor
- Collect kernel version inventory from Linux hosts and flag systems running unpatched ntb_netdev builds
- Correlate memory pressure metrics (MemAvailable, slab pressure, OOM events) with NTB interface stalls
How to Mitigate CVE-2026-74626
Immediate Actions Required
- Identify hosts loading the ntb_netdev module with lsmod | grep ntb_netdev and prioritize them for patching
- Apply the stable-kernel update containing the upstream fix commits listed in the references
- Where patching is delayed, reduce memory pressure on affected hosts by tuning workloads and enabling swap or memory reservations for the kernel
Patch Information
The fix is merged upstream and backported across multiple stable branches. Rebuild or install a kernel that includes one of the following commits corresponding to your branch: Kernel Git Commit 18781cc0, Kernel Git Commit 272df0f, Kernel Git Commit 3f2a15f, Kernel Git Commit 6d7f8a2, Kernel Git Commit 755fd78, Kernel Git Commit a4e3409, Kernel Git Commit d2121fa, and Kernel Git Commit fcaf8ba.
Workarounds
- Unload ntb_netdev on systems that do not require NTB networking to eliminate exposure entirely
- Schedule periodic driver reload during maintenance windows on unpatched hosts to restore full RX queue depth
- Raise vm.min_free_kbytes to reduce the frequency of skb allocation failures under load
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
