CVE-2025-39742
📋 TL;DR
A divide-by-zero vulnerability in the Linux kernel's RDMA hfi1 driver could cause kernel panic or system crash when the find_hw_thread_mask() function executes with zero num_core_siblings. This affects systems using RDMA hardware with the hfi1 driver, primarily in HPC and data center environments.
💻 Affected Systems
- Linux kernel with hfi1 RDMA driver
📦 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...
Learn more about Linux Kernel →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...
Learn more about Linux Kernel →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...
Learn more about Linux Kernel →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...
Learn more about Linux Kernel →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...
Learn more about Linux Kernel →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...
Learn more about Linux Kernel →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...
Learn more about Linux Kernel →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...
Learn more about Linux Kernel →⚠️ Risk & Real-World Impact
Worst Case
Kernel panic leading to system crash and denial of service, potentially affecting multiple systems in clustered environments.
Likely Case
System crash or instability when RDMA operations trigger the vulnerable code path, causing service disruption.
If Mitigated
No impact if the vulnerable code path isn't triggered or if systems don't use RDMA with hfi1 driver.
🎯 Exploit Status
Requires ability to trigger RDMA operations on affected hardware; not remotely exploitable without local access.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Kernel versions containing the fix commits (1a7cf828ed861de5be1aff99e10f114b363c19d3 and related)
Vendor Advisory: https://git.kernel.org/stable/c/1a7cf828ed861de5be1aff99e10f114b363c19d3
Restart Required: Yes
Instructions:
1. Update Linux kernel to patched version. 2. Reboot system. 3. Verify kernel version and that hfi1 module loads correctly.
🔧 Temporary Workarounds
Disable hfi1 RDMA driver
LinuxPrevent loading of vulnerable kernel module
echo 'blacklist hfi1' >> /etc/modprobe.d/blacklist-hfi1.conf
rmmod hfi1
update-initramfs -u
🧯 If You Can't Patch
- Disable RDMA functionality if not required
- Restrict access to systems using RDMA to trusted users only
🔍 How to Verify
Check if Vulnerable:
Check if hfi1 module is loaded: lsmod | grep hfi1. Check kernel version against affected ranges.Check Version:
uname -rVerify Fix Applied:
Verify kernel version includes fix commits. Test RDMA functionality remains operational.📡 Detection & Monitoring
Log Indicators:
- Kernel panic messages
- Divide error or trap messages in dmesg
- System crash/reboot logs
Network Indicators:
- Unexpected RDMA connection failures
SIEM Query:
source="kernel" AND ("divide error" OR "panic" OR "Oops") AND process="hfi1"🔗 References
- https://git.kernel.org/stable/c/1a7cf828ed861de5be1aff99e10f114b363c19d3
- https://git.kernel.org/stable/c/31d0599a23efdbfe579bfbd1eb8f8c942f13744d
- https://git.kernel.org/stable/c/4b4317b0d758ff92ba96f4e448a8992a6fe607bf
- https://git.kernel.org/stable/c/59f7d2138591ef8f0e4e4ab5f1ab674e8181ad3a
- https://git.kernel.org/stable/c/89fdac333a17ed990b41565630ef4791782e02f5
- https://git.kernel.org/stable/c/9b05e91afe948ed819bf87d7ba0fccf451ed79a6
- https://git.kernel.org/stable/c/9bba1a9994c523b44db64f63b564b4719ea2b7ef
- https://git.kernel.org/stable/c/9d3211cb61a0773a2440d0a0698c1e6e7429f907
- https://git.kernel.org/stable/c/ac53f377393cc85156afdc90b636e84e544a6f96
- https://lists.debian.org/debian-lts-announce/2025/10/msg00007.html
- https://lists.debian.org/debian-lts-announce/2025/10/msg00008.html
