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CVE-2026-64121 Linux CVE debrief

The Linux kernel was vulnerable to a slab-out-of-bounds read issue. The vulnerability was in the ifb (Intermediate Functional Block) network device driver. The ifb_dev_init() function allocated memory for tx_private based on the number of transmit queues (num_tx_queues). However, the ethtool stats callbacks used real_num_rx_queues and real_num_tx_queues, which could be different from num_tx_queues for asymmetric devices. This discrepancy could lead to indexing past the allocated tx_private memory, resulting in a slab-out-of-bounds read. The issue has been resolved by consistently using dev->num_tx_queues for stats strings, count, and data walks.

Vendor
Linux
Product
Unknown
CVSS
Unknown
CISA KEV
Not listed in stored evidence
Original CVE published
2026-07-19
Original CVE updated
2026-07-19
Advisory published
2026-07-19
Advisory updated
2026-07-19

Who should care

System administrators and users of Linux kernel versions prior to the patched version should be aware of this vulnerability. Those using asymmetric network devices with IFB, where the RX queue count exceeds the TX queue count, are particularly at risk.

Technical summary

The vulnerability was caused by inconsistent use of queue counts in the ifb network device driver. Specifically, ifb_dev_init() allocated memory for tx_private based on dev->num_tx_queues, but ethtool stats callbacks used dev->real_num_rx_queues and dev->real_num_tx_queues. This inconsistency could lead to out-of-bounds reads when accessing tx_private. The fix ensures that dev->num_tx_queues is used consistently for stats, preventing the out-of-bounds access.

Defensive priority

High priority for Linux kernel maintainers and users, especially those with asymmetric network device configurations.

Recommended defensive actions

  • Apply the patch to update the ifb driver
  • Use dev->num_tx_queues consistently for stats
  • Verify and update Linux kernel to the latest version
  • Review compensating controls for exposed systems while remediation is scheduled and verified
  • Check relevant monitoring, detection, and logs for exposed assets that need extra review
  • Track exceptions, retest remediated assets, and close the item only after evidence is documented
  • Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up

Evidence notes

The vulnerability was discovered and patched by the Linux kernel community. The patch ensures that the ifb driver correctly handles stats for asymmetric devices. Evidence is limited to public CVE details and supplied source corpus. Defenders should verify Linux kernel versions, IFB configurations, and ethtool stats for affected systems. Additional verification tasks may be needed based on specific network device setups and configurations.

Official resources

AI-assisted PatchSiren debrief based on the supplied source corpus. The CVE record was published on 2026-07-19T16:17:53.663Z and has not been modified since then.