FERRAMENTAS LINUX: Stop Local DoS Attacks: The smc-tools /tmp Vulnerability Explained (Fix & Automation)

A predictable /tmp file in smc-tools (v1.8.6 and below) enables local DoS attacks on SUSE/openSUSE. Learn to check your vulnerability, apply the fix with an automation script, and implement iptables or AppArmor mitigations if you can't update now. Includes practical commands for Ubuntu, Rocky Linux, Fedora, RHEL and SUSE.

Historical context (April 2026): A moderate security issue was fixed in smc-tools v1.8.7 for SUSE Linux Enterprise Server and openSUSE Leap 15.6. The problem? A predictable temporary file in /tmp that allows a local, unprivileged user to crash your SMC (Shared Memory Communications) statistics tool – a classic local denial of service.

But this isn't just about one old patch. The pattern – predictable temporary file creation – repeats across dozens of Linux utilities. Learning how to spot, check, and fix this specific flaw will make you better at handling similar vulnerabilities in tmpwatch, mktemp misuse, or any script that writes to world-writable directories.

Let's make this useful for years, not just for today's update.

1. How to check if you are vulnerable

The vulnerable versions are smc-tools below 1.8.7. Here’s how to check on major distros – not only SUSE.

Ubuntu / Debian

dpkg -l | grep smc-tools
# If installed, check version. Most Ubuntu repos don't include smc-tools by default.
# If you compiled from source: smc_rnics --version

Rocky Linux / RHEL / Fedora

rpm -qa | grep smc-tools
# smc-tools is not standard in base repos. Check EPEL or custom builds.

SUSE / openSUSE (the original affected distro)

zypper info smc-tools | grep Version
# Vulnerable if Version < 1.8.7

Generic test for the vulnerability (works on any Linux)

# Simulate the unsafe behavior: Can a normal user create a file that the root-run smc tool will trust?
touch /tmp/smc_trace_workfile_$$
chmod 777 /tmp/smc_trace_workfile_$$
# If the smc tool later writes to that same predictable path without checking, you're vulnerable.
# The actual exploit: user creates a symlink pointing to /etc/passwd or a critical file, then smc tool follows it.

Real example: A local user runs ln -s /etc/crontab /tmp/smc_trace_workfile_1234. Then, when root runs smc_rnics --stats, the tool overwrites /etc/crontab with garbage → system breaks.

2. Automation script to apply the fix

Save this as fix_smc_tmp.sh and run as root. It detects your distro and updates smc-tools to the safe version (1.8.7 or higher).

#!/bin/bash
# fix_smc_tmp.sh - Update smc-tools to fix predictable /tmp DoS
# Works on SUSE, Ubuntu (if available), Rocky (if from source/EPEL)
set -e

echo "[+] Checking current smc-tools version..."
if command -v smc_rnics &> /dev/null; then
    CURRENT_VER=$(smc_rnics --version 2>&1 | head -n1 | grep -oP '\d+\.\d+\.\d+' || echo "0.0.0")
    echo "Found version: $CURRENT_VER"
else
    CURRENT_VER="0.0.0"
    echo "smc-tools not installed. Installing now."
fi

if [[ "$CURRENT_VER" > "1.8.6" ]] || [[ "$CURRENT_VER" == "1.8.7" ]]; then
    echo "Already safe. Exiting."
    exit 0
fi

echo "[+] Updating smc-tools..."
if [ -f /etc/os-release ]; then
    . /etc/os-release
    case "$ID" in
        opensuse-leap|suse|sles)
            zypper refresh && zypper update -y smc-tools
            ;;
        ubuntu|debian)
            echo "smc-tools not in default repos. Compiling from source:"
            apt update && apt install -y git make gcc
            git clone https://github.com/ibm-s390-linux/smc-tools.git /tmp/smc-tools
            cd /tmp/smc-tools && make && make install
            ;;
        rocky|rhel|centos)
            echo "Enable EPEL or compile from source:"
            dnf install -y epel-release || yum install -y epel-release
            dnf install -y smc-tools || yum install -y smc-tools
            ;;
        *)
            echo "Unsupported distro. Manually compile from https://github.com/ibm-s390-linux/smc-tools"
            exit 1
            ;;
    esac
fi

echo "[+] Fix applied. New version: $(smc_rnics --version 2>&1 | head -n1)"

Run it: chmod +x fix_smc_tmp.sh && sudo ./fix_smc_tmp.sh

3. Alternative mitigation if you can't update now

You can't always reboot or upgrade. Here are three immediate workarounds that block the attack vector.

Option A: iptables (doesn't help – this is local, not network)

Correction: iptables won't stop a local user. Instead, use filesystem restrictions:

# Make /tmp immutable to predictable patterns? Not practical. Better:
# Restrict which users can run smc tools:
chmod 700 /usr/bin/smc_rnics
# Only root and group 'smcadmin' can execute. Add trusted users to that group.

Option B: AppArmor profile (effective for SUSE/Ubuntu)

Create /etc/apparmor.d/usr.bin.smc_rnics:

/usr/bin/smc_rnics {
  # Allow read/write only in /tmp/ with random names, not predictable ones
  /tmp/smc_trace_workfile_[0-9]* rw,
  # Deny symlink following in /tmp
  deny /tmp/** l,
}

Then apparmor_parser -r /etc/apparmor.d/usr.bin.smc_rnics

Option C: Monitor and alert (if you're a managed service provider)

# Watch for attempts to create the dangerous file pattern
inotifywait -m /tmp -e create | grep --line-buffered "smc_trace_workfile" | while read line; do
    logger "ALERT: smc-tools predictable tmp file creation attempt by $(stat -c '%U' $(echo $line | cut -d' ' -f3))"
    # Optional: kill the offending user's processes
done

Suggeted reading

Linux Security Cookbook by Daniel J. Barrett - Amazon

Why this matter ?

This vulnerability is a textbook example of CWE-377: Insecure Temporary File. The Cookbook dedicates 20+ pages to patterns like mktemp, O_EXCL, and AppArmor policies. Instead of chasing every single CVE, buy the book, read Chapter 7 ("Files and Filesystems"), and you'll learn how to audit your own code and system scripts for the same flaw.

Affiliate disclosure: As an Amazon Associate, I earn from qualifying purchases. This helps me keep writing in-depth security guides – at no extra cost to you.)