CVE-2026-53188

What it actually does

This is a Linux kernel RDMA core input-validation flaw in the handling of file descriptors passed to ib_get_ucaps(). The vulnerable logic relied on a device number check, but character and block devices can alias the same dev_t value. A local user could potentially pass a file descriptor for a non-authentic device that appears to match the expected RDMA user-capability character device, causing the kernel to treat the wrong file object as trusted RDMA-related input. Depending on reachable code paths and kernel configuration, this may result in incorrect authorization decisions, kernel memory misuse, denial of service through a crash, or other local privilege-impacting behavior. The fix adds validation of the file operations structure so only genuine RDMA capability character devices are accepted.

Why it matters to the business

Systems using affected Linux kernels, especially hosts with RDMA-capable hardware, InfiniBand, RoCE, high-performance networking, storage, virtualization, or HPC workloads, may be exposed to a local kernel attack surface. Successful exploitation could disrupt critical workloads through kernel instability or potentially let an already-local attacker increase their control over the host. The vulnerability is not currently listed in CISA KEV, has no reported ransomware association, and has a low EPSS score, so broad active exploitation is not indicated; however, kernel flaws should still be prioritized where untrusted local users, containers, shared compute, or RDMA devices are present.

How an attack unfolds

An attacker first needs local code execution or the ability to run a process on a vulnerable Linux host. They identify whether RDMA-related kernel interfaces are present and whether they can open relevant device files. Instead of supplying a legitimate RDMA user-capability character device file descriptor, the attacker attempts to find or create a condition where another device, such as a block device, has a matching dev_t value and can be passed to the vulnerable RDMA path. Because the vulnerable kernel logic trusts the device number alone, the attacker-controlled or unrelated file descriptor may be accepted as if it were an authentic RDMA capability device. The attacker then drives the affected ioctl or syscall path to trigger incorrect kernel behavior. Practical impact depends on kernel version, configuration, device availability, and reachable RDMA code paths; likely outcomes include denial of service and, in more severe cases, local privilege escalation or kernel information exposure.

How to fix it

Upgrade to a Linux kernel version that includes the RDMA/core fix validating file operations for ib_get_ucaps(). Because no product-specific fixed versions were provided, obtain the corrected kernel from the relevant Linux distribution, appliance vendor, cloud image provider, or upstream stable kernel stream. Prioritize updates on systems with RDMA, InfiniBand, RoCE, high-performance storage/networking, virtualization hosts, shared compute, and environments where untrusted users or containers can run local code. If immediate patching is not possible, reduce exposure by disabling unused RDMA/InfiniBand modules, restricting access to RDMA device nodes, limiting local shell access, enforcing least privilege for users and containers, and applying device cgroup, SELinux, AppArmor, or udev rules to prevent untrusted workloads from opening sensitive device files. Reboot or live-patch as required for the kernel fix to take effect.

How to confirm the fix worked

Confirm that the running kernel, not just the installed kernel package, includes the vendor fix for the RDMA/core ib_get_ucaps() file-operations validation. Validate with the distribution advisory, kernel changelog, package version, or source commit history. Check the active kernel using uname -r and compare it to the vendor-fixed release. On hosts where RDMA is not required, verify that RDMA modules are not loaded and RDMA device nodes are absent or inaccessible to untrusted users. Review permissions on /dev/infiniband and related device nodes, and confirm container/device policies do not expose RDMA devices unnecessarily. After patching, reboot into the fixed kernel or confirm live-patch coverage if using kernel live patching.

Typical attack path

1. Gain local execution on a vulnerable Linux system, such as through a shell, compromised user account, container escape precondition, or workload execution path.
2. Check for RDMA-related kernel support and accessible device nodes, commonly under RDMA or InfiniBand device interfaces.
3. Identify a non-authentic character or block device file descriptor that can satisfy the vulnerable dev_t-based check.
4. Invoke the RDMA capability retrieval path using the masquerading file descriptor instead of a legitimate RDMA capability character device.
5. Trigger kernel confusion or unsafe handling caused by accepting the wrong file object.
6. Use the resulting condition to crash the kernel, gather sensitive information, or attempt further local privilege escalation, depending on exploitability in the deployed kernel.

How to detect it

There is no reliable single log entry that proves exploitation. Focus on local host telemetry and kernel evidence. Review kernel logs from dmesg, journald, syslog, crash dumps, and kdump for oops, panic, general protection fault, use-after-free, NULL pointer dereference, or warning traces involving RDMA, uverbs, ib_core, or ib_get_ucaps(). Review auditd, eBPF, EDR, or syscall telemetry for untrusted processes opening RDMA device nodes under /dev/infiniband or related RDMA interfaces and then interacting with block devices or issuing unusual ioctl calls. Investigate unexpected kernel crashes on RDMA-capable systems, especially when preceded by activity from non-administrative users or containers. If threat hunting, compare normal workload access to RDMA devices against anomalous processes, recently dropped binaries, temporary-directory execution, and privilege escalation attempts. Because this CVE is not known to be exploited in the wild and has no public exploit maturity indicated, absence of these artifacts does not prove safety; patch validation remains the primary control.

• ib_get_ucaps
• /dev/infiniband/
• ib_core
• uverbs
• RDMA/core

What your security team should do

• Inventory Linux systems with RDMA, InfiniBand, RoCE, or high-performance networking/storage kernel modules enabled.
• Prioritize remediation for shared-user systems, HPC clusters, virtualization hosts, Kubernetes/container hosts, and any system where untrusted local code can execute.
• Apply vendor kernel updates that include the RDMA/core ib_get_ucaps() validation fix, then reboot or confirm live-patch activation.
• If RDMA is not required, disable or unload RDMA-related modules and remove unnecessary device exposure from containers and user sessions.
• Restrict access to RDMA and block device nodes using udev permissions, Linux groups, cgroups device policies, SELinux, or AppArmor.
• Monitor for kernel crashes, oops messages, and unusual local processes accessing both RDMA device nodes and block devices.
• Treat any suspected exploitation as a local kernel compromise investigation, including memory capture where feasible and full review of privileged account activity.