CVE-2026-31493

What it actually does

This is a use-after-free flaw in the Linux kernel EFA RDMA driver’s admin queue completion handling. When an EFA admin command completes with an error, the driver may reference the command completion context after that context has already been freed by the polling or interrupt completion path. Because the freed memory may contain stale data or may have been reallocated for another kernel object, subsequent reads or logging from that context can expose kernel memory, trigger kernel instability, or potentially contribute to privilege escalation or arbitrary kernel memory corruption under favorable heap-reuse conditions. The issue is local: an attacker generally needs authenticated local code execution and the ability to interact with the affected RDMA/EFA device path.

Why it matters to the business

Systems running affected Linux kernels with the EFA RDMA driver enabled may be exposed to local compromise, data leakage, or denial of service. The main operational risk is to high-performance compute, cloud, AI/ML, and low-latency workloads that rely on EFA/RDMA networking, where disabling the driver may affect application performance or connectivity. Although public exploit maturity is currently listed as none, the CVSS score is high and the impact includes confidentiality, integrity, and availability, so affected systems should be patched through normal kernel maintenance cycles or faster where untrusted users, containers, or multi-tenant workloads can access RDMA devices.

How an attack unfolds

An attacker first obtains local execution on a Linux system that has the affected EFA RDMA driver present and reachable. They then interact with RDMA/EFA interfaces in a way that causes admin queue commands to complete with errors. During error handling, the vulnerable driver path attempts to print or use fields from the completion context after that context has already been freed. If the attacker can influence timing and memory reuse, the freed context may contain stale kernel data or data from a newly allocated object, which can lead to information disclosure, kernel crash, or potentially further exploitation inside kernel memory. Practical exploitation depends heavily on EFA hardware availability, kernel build options, device permissions, allocator behavior, and whether untrusted local users or containers can reach RDMA device nodes.

How to fix it

Upgrade to a Linux kernel or vendor kernel package that includes the RDMA/efa fix for symmetric allocation and deallocation of the admin completion context. No exact fixed upstream or distribution package versions were provided in the input, so use the fixed kernel advisory from the relevant Linux distribution, cloud image provider, appliance vendor, or kernel maintainer. Reboot systems after installing the fixed kernel to ensure the vulnerable kernel and module are no longer running. Where immediate patching is not possible, reduce exposure by unloading or blacklisting the efa kernel module if EFA is not required, disabling EFA/RDMA functionality for affected workloads, and restricting access to RDMA device nodes such as /dev/infiniband/* to only trusted users and services. In containerized or multi-user environments, prevent untrusted workloads from being granted RDMA device access until patched.

How to confirm the fix worked

Confirm remediation by verifying that the running kernel is the fixed vendor build, not just that a fixed package is installed. Check the active kernel with uname -r and compare it against the vendor advisory or package changelog that references this vulnerability or the RDMA/efa admin completion context fix. Confirm whether the EFA driver is loaded with lsmod, modinfo efa, or equivalent tooling, and verify whether EFA/RDMA devices are present under /dev/infiniband. After reboot, review dmesg or journalctl -k to confirm the expected kernel version and absence of repeated EFA admin queue errors, kernel oops messages, or KASAN use-after-free reports. For systems where EFA is not required, validate that the efa module cannot be loaded and that RDMA device nodes are absent or inaccessible to untrusted users.

Typical attack path

1. Gain local authenticated code execution on a Linux system running an affected kernel.
2. Confirm that the EFA RDMA driver is loaded or that EFA/RDMA device nodes are accessible.
3. Open or interact with RDMA/EFA interfaces, commonly through /dev/infiniband device nodes or RDMA libraries/tools.
4. Trigger EFA admin queue operations that fail and enter the vulnerable error completion path.
5. Race or shape kernel heap reuse so the freed completion context contains attacker-useful or attacker-influenced data.
6. Leverage the resulting use-after-free behavior for kernel information disclosure, denial of service, or as part of a broader local privilege-escalation chain.

How to detect it

There are no known public exploit indicators and no KEV listing for this vulnerability at the time of the provided data. Detection should focus on signs of attempted local kernel exploitation or instability on systems with the EFA RDMA driver. Review kernel logs from dmesg, journalctl -k, /var/log/kern.log, /var/log/messages, and crash dumps for EFA driver errors, admin queue failures, kernel oopses, panics, general protection faults, and KASAN use-after-free reports. Correlate these events with audit, EDR, process accounting, or shell history showing local users or containers accessing /dev/infiniband/*, running RDMA utilities, or loading RDMA-related libraries shortly before the crash or warning. In multi-tenant or containerized environments, review container runtime configuration and audit logs for RDMA device passthrough or unusual access to infiniband character devices. Because the vulnerable behavior occurs in kernel memory and may only manifest as a crash or generic memory-corruption symptom, absence of logs does not prove absence of exploitation.

What your security team should do

• Inventory Linux systems using EFA/RDMA, especially HPC, AI/ML, low-latency, and cloud instance types that expose EFA devices.
• Prioritize patching systems where untrusted local users, shared compute jobs, or containers can access RDMA device nodes.
• Upgrade to the vendor-fixed kernel and reboot; confirm the running kernel version after reboot.
• If patching is delayed, restrict permissions on /dev/infiniband/* and remove RDMA device passthrough from untrusted containers or workloads.
• Disable, unload, or blacklist the efa module on systems that do not require EFA functionality.
• Enable kernel crash, audit, and EDR telemetry for local privilege-escalation attempts and kernel instability on affected systems.
• Search historical kernel logs for EFA-related errors, KASAN use-after-free reports, kernel oopses, or unexplained crashes around RDMA activity.
• Monitor vendor kernel advisories because exact fixed package versions may vary by distribution and downstream kernel branch.