Patch

CVE-2016-6210

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Vulnerability Overview

CVE Name

CVE-2016-6210

Severity

5.9

Medium

CVE Description

sshd in OpenSSH before 7.3, when SHA256 or SHA512 are used for user password hashing, uses BLOWFISH hashing on a static password when the username does not exist, which allows remote attackers to enumerate users by leveraging the timing difference between ...

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Latest Patch info

There is no patch available at the moment, but you can use our script.

Patch Name

https://cert-portal.siemens.com/productcert/pdf/ssa-412672.pdf

Date

15.12.2022

Script

Script Type

Remediation script

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🔒 SSH Configuration Hardening to Mitigate CVE-2016-6210 This script mitigates CVE-2016-6210, a vulnerability in OpenSSH that can allow remote attackers to infer valid usernames through timing differences. The script disables password-based authentication and restricts SSH access to specific users, reducing the attack surface and enhancing the overall security of your SSH server. 🔍 How it works: Disables password authentication: The script modifies the SSH configuration to disable password-based authentication, enforcing the use of more secure methods like key-based authentication. Restricts SSH access: It allows SSH access only to a predefined list of users by adding the AllowUsers directive to the SSH configuration file. Backup and restart: A backup of the SSH configuration file is created before making changes, and the SSH service is restarted to apply the new settings. ⚠️ Why it matters: CVE-2016-6210 can be exploited to gather information about valid usernames on a system by measuring the response time differences during authentication attempts. By disabling password authentication and restricting SSH access to specific users, this script mitigates the risk of attackers exploiting this vulnerability, enhancing the security of the SSH service.

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#!/bin/bash

SSHD_CONFIG="/usr/local/etc/sshd_config"
SSHD_BINARY="/usr/local/sbin/sshd"

disable_password_auth() {

if [ ! -f "$SSHD_CONFIG.bak" ]; then
        cp $SSHD_CONFIG "$SSHD_CONFIG.bak"
        echo "Backup of the SSH configuration created at $SSHD_CONFIG.bak"
    fi

sed -i 's/#PasswordAuthentication yes/PasswordAuthentication no/' $SSHD_CONFIG
    sed -i 's/PasswordAuthentication yes/PasswordAuthentication no/' $SSHD_CONFIG
    sed -i 's/#PasswordAuthentication no/PasswordAuthentication no/' $SSHD_CONFIG

echo "Password authentication has been disabled."
}

restrict_ssh_access() {
    ALLOWED_USERS=("osboxes@192.168.1.100" "lauti@mydomain.com")  # Replace with your specific users and hosts

if ! grep -q "AllowUsers" $SSHD_CONFIG; then
        echo -n "AllowUsers " >> $SSHD_CONFIG
        for user in "${ALLOWED_USERS[@]}"; do
            echo -n "$user " >> $SSHD_CONFIG
        done
        echo ""

echo "SSH access restricted to: ${ALLOWED_USERS[*]}"
    else
        echo "AllowUsers directive already present in $SSHD_CONFIG"
    fi
}

disable_password_auth
restrict_ssh_access

sudo kill $(pgrep -f "$SSHD_BINARY")
$SSHD_BINARY -f $SSHD_CONFIG

echo "SSH configuration updated and service restarted."

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Affected OS & Apps

Openssh

Openbsd

4.8

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