CVE-2025-37961

5.5 MEDIUM

📋 TL;DR

This CVE describes an uninitialized memory vulnerability in the Linux kernel's IPVS (IP Virtual Server) subsystem. The flaw occurs when the do_output_route4 function reads an uninitialized source address (saddr) value, which can cause routing failures and potentially lead to kernel memory disclosure or denial of service. Systems running affected Linux kernel versions with IPVS enabled are vulnerable.

💻 Affected Systems

Products:

Linux kernel

Versions: Specific affected versions not explicitly stated in CVE, but based on commit history likely affects multiple stable kernel branches before fixes were backported.

Operating Systems: Linux distributions using vulnerable kernel versions

Default Config Vulnerable: ✅ No

Notes: Only vulnerable when IPVS is enabled and configured to use tunnel modes. Most default Linux installations do not have IPVS enabled.

📦 What is this software?

Debian Linux by Debian

View all CVEs affecting Debian Linux →

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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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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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 →

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 →

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 memory disclosure leading to information leakage, potential privilege escalation if combined with other vulnerabilities, or denial of service through kernel crashes.

🟠

Likely Case

Routing failures causing network connectivity issues for IPVS-managed services, potentially leading to service disruption.

🟢

If Mitigated

Minimal impact if IPVS is not enabled or if systems are not using tunnel modes that trigger this code path.

🌐 Internet-Facing: MEDIUM - Exploitation requires specific network conditions and IPVS configuration, but could affect load balancers and proxies.

🏢 Internal Only: LOW - Requires IPVS tunnel configuration and specific traffic patterns to trigger.

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: UNKNOWN

Unauthenticated Exploit: ⚠️ Yes

Complexity: MEDIUM

Exploitation requires sending specific network traffic to trigger the vulnerable code path in IPVS tunnel handling.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Fixed in kernel commits: 0160ac84fb03a0bd8dce8a42cb25bfaeedd110f4, 7d0032112a0380d0b8d7c9005f621928a9b9fc76, a3a1b784791a3cbfc6e05c4d8a3c321ac5136e25, adbc8cc1162951cb152ed7f147d5fbd35ce3e62f, e34090d7214e0516eb8722aee295cb2507317c07

Vendor Advisory: https://git.kernel.org/stable/c/0160ac84fb03a0bd8dce8a42cb25bfaeedd110f4

Restart Required: Yes

Instructions:

1. Update Linux kernel to version containing the fix. 2. Check distribution-specific security advisories for backported patches. 3. Reboot system after kernel update.

🔧 Temporary Workarounds

Disable IPVS

linux

Disable the IPVS subsystem if not required for your infrastructure.

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

Disable tunnel modes

linux

Avoid using IPVS tunnel configurations that trigger the vulnerable code path.

🧯 If You Can't Patch

Implement network segmentation to isolate IPVS-managed services
Use alternative load balancing solutions until patching is possible

🔍 How to Verify

Check if Vulnerable:

Check if IPVS modules are loaded: lsmod | grep ip_vs. Check kernel version against patched versions.

Check Version:

uname -r

Verify Fix Applied:

Verify kernel version includes one of the fix commits. Check dmesg for related error messages after update.

📡 Detection & Monitoring

Log Indicators:

Kernel panic logs
KMSAN error messages in dmesg
IPVS routing failure logs

Network Indicators:

Unexpected routing failures for IPVS-managed services
Increased packet loss on tunnel interfaces

SIEM Query:

source="kernel" AND ("KMSAN" OR "uninit-value" OR "ip_vs_xmit")

📊 Metadata

CVE ID: CVE-2025-37961

CVSS v3 Score: 5.5 (MEDIUM)

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

CWE: CWE-908

EPSS Score: 0.04% exploit probability (11.1th percentile)

Published: May 20, 2025

Last Updated: December 16, 2025

🔗 References