CVE-2021-47616 – This CVE describes a use-after-free vulnerabili... (How to Fix)

Q: What is the severity of CVE-2021-47616?

CVE-2021-47616 has a CVSS score of 7.8 (HIGH). This CVE describes a use-after-free vulnerability in the Linux kernel's RDMA subsystem. An attacker could exploit this to cause a kernel crash or potentially execute arbitrary code with kernel privileges. Systems using RDMA (Remote Direct Memory Access) features in affected Linux kernel versions are vulnerable.

📋 TL;DR

This CVE describes a use-after-free vulnerability in the Linux kernel's RDMA subsystem. An attacker could exploit this to cause a kernel crash or potentially execute arbitrary code with kernel privileges. Systems using RDMA (Remote Direct Memory Access) features in affected Linux kernel versions are vulnerable.

💻 Affected Systems

Products:

Linux kernel

Versions: Specific affected versions not explicitly stated in CVE description, but patches were applied to stable kernel trees. Likely affects multiple kernel versions before the fix.

Operating Systems: Linux distributions using affected kernel versions

Default Config Vulnerable: ✅ No

Notes: Only vulnerable if RDMA subsystem is enabled and in use. Many standard Linux installations don't enable RDMA by default.

📦 What is this software?

Linux Kernel by Linux

The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...

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⚠️ Risk & Real-World Impact

🔴

Worst Case

Kernel panic leading to system crash, or potential privilege escalation to kernel-level code execution allowing complete system compromise.

🟠

Likely Case

Kernel crash causing denial of service, system instability, or potential information disclosure from kernel memory.

🟢

If Mitigated

Limited to denial of service if exploit fails or system has additional protections like kernel address space layout randomization (KASLR).

🌐 Internet-Facing: LOW - RDMA is typically used in high-performance computing clusters and data centers, not directly internet-facing services.

🏢 Internal Only: MEDIUM - Exploitation requires local access or network access to RDMA services, which are common in internal high-performance computing environments.

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: UNKNOWN

Unauthenticated Exploit: ✅ No

Complexity: MEDIUM

Exploitation requires triggering the specific error path in rxe_qp_from_init() function, which may require specific RDMA operations or error conditions.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Patches available in stable kernel trees via the provided git commits

Vendor Advisory: https://git.kernel.org/stable/c/84b01721e8042cdd1e8ffeb648844a09cd4213e0

Restart Required: Yes

Instructions:

1. Update Linux kernel to version containing the fix. 2. Check with your distribution vendor for specific patched kernel versions. 3. Reboot system after kernel update.

🔧 Temporary Workarounds

Disable RDMA subsystem

linux

Prevent exploitation by disabling the RDMA subsystem if not required

modprobe -r rdma_rxe
echo 'blacklist rdma_rxe' >> /etc/modprobe.d/blacklist.conf

Restrict RDMA access

linux

Limit which users or processes can access RDMA devices

chmod 600 /dev/infiniband/*
setfacl -m u:root:rw /dev/infiniband/*

🧯 If You Can't Patch

Disable RDMA subsystem entirely if not needed
Implement strict access controls to limit which users can trigger RDMA operations

🔍 How to Verify

Check if Vulnerable:

Check kernel version and if RDMA modules are loaded: 'uname -r' and 'lsmod | grep rdma'

Check Version:

uname -r

Verify Fix Applied:

Verify kernel version is updated and check if the specific git commit is included in your kernel source

📡 Detection & Monitoring

Log Indicators:

Kernel panic messages
OOM killer activity related to RDMA
System crashes or instability when RDMA operations fail

Network Indicators:

Unusual RDMA traffic patterns
Failed RDMA connection attempts

SIEM Query:

source="kernel" AND ("panic" OR "Oops" OR "BUG") AND "rdma"

📊 Metadata

CVE ID: CVE-2021-47616

CVSS v3 Score: 7.8 (HIGH)

CVSS Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

CWE: CWE-416

Published: June 19, 2024

Last Updated: November 21, 2024

🔗 References

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