Hack The Sec-Leading Resource Of Linux Tutorial: Linux_ssh

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<span style="color: #990000;"><u><i>Deny/Allow Access for Users & Groups in OpenSSH</i></u></span></h2>
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<span style="font-family: Georgia, Times New Roman, serif;">For security purposes many times we required to restrict or allow for SSH access for specific Users or Groups. To make any changes edit <b>OpenSSH </b>configuration file <span style="color: red;">/etc/ssh/sshd_config</span> and do required changes for allowing or denying any user or group.</span></div>
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<span style="color: #0b5394;">Allow/Deny Users and Groups:</span></h2>
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<span style="font-family: Georgia, Times New Roman, serif;">To allow or deny any user or group on OpenSSH, first edit configuration file<span style="border-image-outset: initial; border-image-repeat: initial; border-image-slice: initial; border-image-source: initial; border-image-width: initial; border: 0px; font-size: inherit; font-weight: 700; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"><span style="color: red;">/etc/ssh/sshd_config</span></span> in your favorite editor and do changes as following examples.</span></div>
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<span style="font-family: Georgia, Times New Roman, serif;"><u><span style="border-image-outset: initial; border-image-repeat: initial; border-image-slice: initial; border-image-source: initial; border-image-width: initial; border: 0px; font-size: inherit; font-weight: 700; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"><span style="color: #0b5394;">1. Deny Users:</span></span> </u>To restrict for block specific user for SSH on server add the following rules. For example to restrict users raj, john and sarah.</span></div>
<pre class="pretty" style="background: none 0px 0px repeat scroll rgb(240, 240, 240); border-left-color: rgb(116, 183, 63); border-left-width: 3px; border-radius: 5px; border-style: none none none solid; line-height: 1.5em; margin-bottom: 20px; outline: 0px; overflow: auto; padding: 8px 20px 8px 18px; vertical-align: baseline;"><span style="font-family: Courier New, Courier, monospace; font-size: large;"><orange><span style="color: #990000;">DenyUsers</span></orange>  raj  john  sarah
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<span style="font-family: Georgia, Times New Roman, serif;"><span style="border-image-outset: initial; border-image-repeat: initial; border-image-slice: initial; border-image-source: initial; border-image-width: initial; border: 0px; font-size: inherit; font-weight: 700; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"><span style="color: #0b5394;"><u>2. Deny Groups:</u></span></span> In place of restricting specific users we can also restrict groups in OpenSSH. For example to restrict support and marketing groups from ssh add following rules.</span></div>
<pre class="pretty" style="background: none 0px 0px repeat scroll rgb(240, 240, 240); border-left-color: rgb(116, 183, 63); border-left-width: 3px; border-radius: 5px; border-style: none none none solid; line-height: 1.5em; margin-bottom: 20px; outline: 0px; overflow: auto; padding: 8px 20px 8px 18px; vertical-align: baseline;"><span style="font-family: Courier New, Courier, monospace; font-size: large;"><span style="color: #990000;"><orange>DenyGroups</orange>  </span>support  marketing</span><span style="font-size: 0.9em;">
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<span style="font-family: Georgia, Times New Roman, serif;"><span style="border-image-outset: initial; border-image-repeat: initial; border-image-slice: initial; border-image-source: initial; border-image-width: initial; border: 0px; font-size: inherit; font-weight: 700; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"><span style="color: #0b5394;"><u>3. Allow Users:</u></span></span> By default all users are allowed to login to OpenSSH server. But we can specifically allow any user, For example hackthesec and linuxos belongs to support group and we already have restricted that group members. So we can specify that users in Allow users to allow them specifically.</span></div>
<pre class="pretty" style="background: none 0px 0px repeat scroll rgb(240, 240, 240); border-left-color: rgb(116, 183, 63); border-left-width: 3px; border-radius: 5px; border-style: none none none solid; line-height: 1.5em; margin-bottom: 20px; outline: 0px; overflow: auto; padding: 8px 20px 8px 18px; vertical-align: baseline;"><span style="font-family: Courier New, Courier, monospace; font-size: large;"><span style="color: #990000;"><orange>AllowUsers</orange>  </span>hackthesec  linuxos
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<span style="font-family: Georgia, Times New Roman, serif;"><span style="border-image-outset: initial; border-image-repeat: initial; border-image-slice: initial; border-image-source: initial; border-image-width: initial; border: 0px; font-size: inherit; font-weight: 700; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"><span style="color: #0b5394;"><u>4. Allow Groups:</u></span></span> Similarly we can allow all the members of specific group which may be denied in any other group. For example user andrew and peter belongs to marketing group as well as admin group. So we can allow access to both users by allowing admin group.</span></div>
<pre class="pretty" style="background: none 0px 0px repeat scroll rgb(240, 240, 240); border-left-color: rgb(116, 183, 63); border-left-width: 3px; border-radius: 5px; border-style: none none none solid; line-height: 1.5em; margin-bottom: 20px; outline: 0px; overflow: auto; padding: 8px 20px 8px 18px; vertical-align: baseline;"><span style="font-family: Courier New, Courier, monospace; font-size: large;"><span style="color: #990000;"><orange>AllowGroups</orange>  </span>admin
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<span style="color: #0b5394;"><u>Restart OpenSSH:</u></span></h2>
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<span style="font-family: Georgia, Times New Roman, serif;">After doing any changes in configuration file, make sure to restart <b>OpenSSH </b>service as following.</span></div>
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</span><span style="color: lime;"># systemd restart sshd</span></span></pre>
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How to Deny/Allow Access for Users & Groups in OpenSSH

Deny/Allow Access for Users & Groups in OpenSSH For security purposes many times we required to restrict or allow for SSH access fo...