Q:

How do I select multiple elements with the same name using xmlstarlet?

I have the following xml:
<a>
  <TICKET_LIST>
    <TICKET>
      <NUMBER>182820</NUMBER>
      <DETECTION>
        <IP network_id="173230">192.168.140.61</IP>
        <DNSNAME><![CDATA[local]]></DNSNAME>
        <PORT>80</PORT>
        <SERVICE>CGI</SERVICE>
        <PROTOCOL>tcp</PROTOCOL>
      </DETECTION>
      <VULNINFO>
        <TITLE><![CDATA[HTTP TRACE / TRACK Methods Enabled]]></TITLE>
        <TYPE>VULN</TYPE>
        <QID>12680</QID>
        <SEVERITY>3</SEVERITY>
        <STANDARD_SEVERITY>3</STANDARD_SEVERITY>
        <CVE_ID_LIST>
          <CVE_ID><![CDATA[CVE-2004-2320]]></CVE_ID>
          <CVE_ID><![CDATA[CVE-2010-0386]]></CVE_ID>
          <CVE_ID><![CDATA[CVE-2003-1567]]></CVE_ID>
        </CVE_ID_LIST>
      </VULNINFO>
    </TICKET>
    <TICKET>
      <NUMBER>182957</NUMBER>
      <DETECTION>
        <IP network_id="173230">192.168.200.46</IP>
        <DNSNAME><![CDATA[local]]></DNSNAME>
        <PORT>443</PORT>
        <SERVICE>Web server</SERVICE>
        <PROTOCOL>tcp</PROTOCOL>
      </DETECTION>
      <VULNINFO>
        <TITLE><![CDATA[Web Server Uses Plain-Text Form Based Authentication]]></TITLE>
        <TYPE>VULN</TYPE>
        <QID>86728</QID>
        <SEVERITY>3</SEVERITY>
        <STANDARD_SEVERITY>3</STANDARD_SEVERITY>
      </VULNINFO>
    </TICKET>
  </TICKET_LIST>
</a>

I would like to export some data to a csv format.
This code returns some the data as expected:
xmlstarlet  sel -T -t -m /a/TICKET_LIST/TICKET  -v "concat(NUMBER,',',DETECTION/IP,',',DETECTION/DNSNAME,',',DETECTION/SERVICE,',',DETECTION/PORT,',',VULNINFO/TITLE,',',VULNINFO/QID)" -n file.xml

However I am also interested in all CVE_ID data on the same line as the rest of the data.
Result I am getting now is:
182820,192.168.140.61,local,CGI,80,HTTP TRACE / TRACK Methods Enabled,12680
182957,192.168.200.46,local,Web server,443,Web Server Uses Plain-Text Form Based Authentication,86728

Expected results is:
182820,192.168.140.61,local,CGI,80,HTTP TRACE / TRACK Methods Enabled,12680,CVE-2004-2320 CVE-2010-0386 CVE-2003-1567
182957,192.168.200.46,local,Web server,443,Web Server Uses Plain-Text Form Based Authentication,86728

A:

Since there are multiple CVE_ID elements, you'll need to add another match (-m) matching VULNINFO/CVE_ID_LIST/CVE_ID. 
Also, to get the newline (-n) to output correctly you'll have to break nesting (-b).
Example... 
xmlstarlet sel -T -t -m /a/TICKET_LIST/TICKET -v "concat(NUMBER,',',DETECTION/IP,',',DETECTION/DNSNAME,',',DETECTION/SERVICE,',',DETECTION/PORT,',',VULNINFO/TITLE,',',VULNINFO/QID,',')" -m VULNINFO/CVE_ID_LIST/CVE_ID -v "concat(.,' ')" -b -n file.xml

Output...
182820,192.168.140.61,local,CGI,80,HTTP TRACE / TRACK Methods Enabled,12680,CVE-2004-2320 CVE-2010-0386 CVE-2003-1567
182957,192.168.200.46,local,Web server,443,Web Server Uses Plain-Text Form Based Authentication,86728,

The command line might make more sense if you see the XSLT that xmlstarlet uses internally (-C)...
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:exslt="http://exslt.org/common" version="1.0" extension-element-prefixes="exslt">
  <xsl:output omit-xml-declaration="yes" indent="no" method="text"/>
  <xsl:template match="/">
    <xsl:for-each select="/a/TICKET_LIST/TICKET">
      <xsl:call-template name="value-of-template">
        <xsl:with-param name="select" select="concat(NUMBER,',',DETECTION/IP,',',DETECTION/DNSNAME,',',DETECTION/SERVICE,',',DETECTION/PORT,',',VULNINFO/TITLE,',',VULNINFO/QID,',')"/>
      </xsl:call-template>
      <xsl:for-each select="VULNINFO/CVE_ID_LIST/CVE_ID">
        <xsl:call-template name="value-of-template">
          <xsl:with-param name="select" select="concat(.,' ')"/>
        </xsl:call-template>
      </xsl:for-each>
      <xsl:value-of select="'&#10;'"/>
    </xsl:for-each>
  </xsl:template>
  <xsl:template name="value-of-template">
    <xsl:param name="select"/>
    <xsl:value-of select="$select"/>
    <xsl:for-each select="exslt:node-set($select)[position()&gt;1]">
      <xsl:value-of select="'&#10;'"/>
      <xsl:value-of select="."/>
    </xsl:for-each>
  </xsl:template>
</xsl:stylesheet>

Note that the second line of the output has a trailing ,. I wouldn't think that would be an issue since the CSV rows would all have the same number of columns. 
If it is a problem, you could use an "if" (-i) and check to see if there are any CVE_ID's before processing them...
xmlstarlet sel -T -t -m /a/TICKET_LIST/TICKET -v "concat(NUMBER,',',DETECTION/IP,',',DETECTION/DNSNAME,',',DETECTION/SERVICE,',',DETECTION/PORT,',',VULNINFO/TITLE,',',VULNINFO/QID)" -i VULNINFO/CVE_ID_LIST/CVE_ID -o "," -m VULNINFO/CVE_ID_LIST/CVE_ID -v "concat(.,' ')" -b -n file.xml

Output is the same as above except the trailing , is not output on the second line...
182820,192.168.140.61,local,CGI,80,HTTP TRACE / TRACK Methods Enabled,12680,CVE-2004-2320 CVE-2010-0386 CVE-2003-1567
182957,192.168.200.46,local,Web server,443,Web Server Uses Plain-Text Form Based Authentication,86728

