Chapter 12. Security

12.1. Why Security is So Important

Bugs are occasionally introduced to the software. Arguably, the most dangerous of them are those opening security vulnerabilities. From the technical viewpoint, such vulnerabilities are to be closed by exterminating the bugs that caused them. However, the policies for handling mere bugs and security vulnerabilities are very different.

A typical small bug affects only those users who have enabled some combination of options triggering the bug. The developer will eventually release a patch followed by a new version of the software, free of the bug, but the majority of users will not take the trouble of upgrading immediately because the bug has never vexed them. A critical bug that may cause data loss represents a graver issue. Nevertheless, prudent users know that a lot of possible accidents, besides software bugs, are likely to lead to data loss, and so they make backups of important data; in addition, a critical bug will be discovered really soon.

A security vulnerability is all different. First, it may remain unnoticed for years because often it does not cause software malfunction. Second, a malicious party can use it to gain unauthorized access to a vulnerable system, to destroy or alter sensitive data; and in the worst case the user will not even notice the harm caused. Third, exposing a vulnerable system often assists attackers to break into other systems that could not be compromised otherwise. Therefore closing a vulnerability alone is not enough: notify the audience of it in the most clear and comprehensive manner, which will allow them to evaluate the danger and take appropriate action.

12.2. Fixing Security Vulnerabilities

While on the subject of ports and packages, a security vulnerability may initially appear in the original distribution or in the port files. In the former case, the original software developer is likely to release a patch or a new version instantly. Update the port promptly with respect to the author’s fix. If the fix is delayed for some reason, either mark the port as FORBIDDEN or introduce a patch file to the port. In the case of a vulnerable port, just fix the port as soon as possible. In either case, follow the standard procedure for submitting changes unless having rights to commit it directly to the ports tree.

Being a ports committer is not enough to commit to an arbitrary port. Remember that ports usually have maintainers, must be respected.

Please make sure that the port’s revision is bumped as soon as the vulnerability has been closed. That is how the users who upgrade installed packages on a regular basis will see they need to run an update. Besides, a new package will be built and distributed over FTP and WWW mirrors, replacing the vulnerable one. Bump PORTREVISION unless DISTVERSION has changed in the course of correcting the vulnerability. That is, bump PORTREVISION if adding a patch file to the port, but do not bump it if updating the port to the latest software version and thus already touched DISTVERSION. Please refer to the corresponding section for more information.

12.3. Keeping the Community Informed

12.3.1. The VuXML Database

A very important and urgent step to take as early after a security vulnerability is discovered as possible is to notify the community of port users about the jeopardy. Such notification serves two purposes. First, if the danger is really severe it will be wise to apply an instant workaround. For example, stop the affected network service or even deinstall the port completely until the vulnerability is closed. Second, a lot of users tend to upgrade installed packages only occasionally. They will know from the notification that they must update the package without delay as soon as a corrected version is available.

Given the huge number of ports in the tree, a security advisory cannot be issued on each incident without creating a flood and losing the attention of the audience when it comes to really serious matters. Therefore security vulnerabilities found in ports are recorded in the FreeBSD VuXML database. The Security Officer Team members also monitor it for issues requiring their intervention.

Committers can update the VuXML database themselves, assisting the Security Officer Team and delivering crucial information to the community more quickly. Those who are not committers or have discovered an exceptionally severe vulnerability should not hesitate to contact the Security Officer Team directly, as described on the FreeBSD Security Information page.

The VuXML database is an XML document. Its source file vuln.xml is kept right inside the port security/vuxml. Therefore the file’s full pathname will be PORTSDIR/security/vuxml/vuln.xml. Each time a security vulnerability is discovered in a port, please add an entry for it to that file. Until familiar with VuXML, the best thing to do is to find an existing entry fitting the case at hand, then copy it and use it as a template.

12.3.2. A Short Introduction to VuXML

The full-blown XML format is complex, and far beyond the scope of this book. However, to gain basic insight on the structure of a VuXML entry only the notion of tags is needed. XML tag names are enclosed in angle brackets. Each opening <tag> must have a matching closing </tag>. Tags may be nested. If nesting, the inner tags must be closed before the outer ones. There is a hierarchy of tags, that is, more complex rules of nesting them. This is similar to HTML. The major difference is that XML is eXtensible, that is, based on defining custom tags. Due to its intrinsic structure XML puts otherwise amorphous data into shape. VuXML is particularly tailored to mark up descriptions of security vulnerabilities.

Now consider a realistic VuXML entry:

<vuln vid="f4bc80f4-da62-11d8-90ea-0004ac98a7b9"> (1)
  <topic>Several vulnerabilities found in Foo</topic> (2)
  <affects>
    <package>
      <name>foo</name> (3)
      <name>foo-devel</name>
      <name>ja-foo</name>
      <range><ge>1.6</ge><lt>1.9</lt></range> (4)
      <range><ge>2.*</ge><lt>2.4_1</lt></range>
      <range><eq>3.0b1</eq></range>
    </package>
    <package>
      <name>openfoo</name> (5)
      <range><lt>1.10_7</lt></range> (6)
      <range><ge>1.2,1</ge><lt>1.3_1,1</lt></range>
    </package>
  </affects>
  <description>
    <body xmlns="http://www.w3.org/1999/xhtml">
      <p>J. Random Hacker reports:</p> (7)
      <blockquote
        cite="http://j.r.hacker.com/advisories/1">
        <p>Several issues in the Foo software may be exploited
          via carefully crafted QUUX requests.  These requests will
          permit the injection of Bar code, mumble theft, and the
          readability of the Foo administrator account.</p>
      </blockquote>
    </body>
  </description>
  <references> (8)
    <freebsdsa>SA-10:75.foo</freebsdsa> (9)
    <freebsdpr>ports/987654</freebsdpr> (10)
    <cvename>CAN-2010-0201</cvename> (11)
    <cvename>CAN-2010-0466</cvename>
    <bid>96298</bid> (12)
    <certsa>CA-2010-99</certsa> (13)
    <certvu>740169</certvu> (14)
    <uscertsa>SA10-99A</uscertsa> (15)
    <uscertta>SA10-99A</uscertta> (16)
    <mlist msgid="201075606@hacker.com">http://marc.theaimsgroup.com/?l=bugtraq&amp;m=203886607825605</mlist> (17)
    <url>http://j.r.hacker.com/advisories/1</url> (18)
  </references>
  <dates>
    <discovery>2010-05-25</discovery> (19)
    <entry>2010-07-13</entry> (20)
    <modified>2010-09-17</modified> (21)
  </dates>
</vuln>

The tag names are supposed to be self-explanatory so we shall take a closer look only at fields which needs to be filled in:

1This is the top-level tag of a VuXML entry. It has a mandatory attribute, vid, specifying a universally unique identifier (UUID) for this entry (in quotes). Generate a UUID for each new VuXML entry (and do not forget to substitute it for the template UUID unless writing the entry from scratch). Use uuidgen(1) to generate a VuXML UUID.
2This is a one-line description of the issue found.
3The names of packages affected are listed there. Multiple names can be given since several packages may be based on a single master port or software product. This may include stable and development branches, localized versions, and slave ports featuring different choices of important build-time configuration options.
4Affected versions of the package(s) are specified there as one or more ranges using a combination of <lt>, <le>, <eq>, <ge>, and <gt> elements. Check that the version ranges given do not overlap.
In a range specification, * (asterisk) denotes the smallest version number. In particular, 2.* is less than 2.a. Therefore an asterisk may be used for a range to match all possible alpha, beta, and RC versions. For instance, <ge>2.</ge><lt>3.</lt> will selectively match every 2.x version while <ge>2.0</ge><lt>3.0</lt> will not since the latter misses 2.r3 and matches 3.b.
The above example specifies that affected are versions 1.6 and up to but not including 1.9, versions 2.x before 2.4_1, and version 3.0b1.
5Several related package groups (essentially, ports) can be listed in the <affected> section. This can be used if several software products (say FooBar, FreeBar and OpenBar) grow from the same code base and still share its bugs and vulnerabilities. Note the difference from listing multiple names within a single <package> section.
6The version ranges have to allow for PORTEPOCH and PORTREVISION if applicable. Please remember that according to the collation rules, a version with a non-zero PORTEPOCH is greater than any version without PORTEPOCH, for example, 3.0,1 is greater than 3.1 or even than 8.9.
7This is a summary of the issue. XHTML is used in this field. At least enclosing <p> and </p> has to appear. More complex mark-up may be used, but only for the sake of accuracy and clarity: No eye candy please.
8This section contains references to relevant documents. As many references as apply are encouraged.
9This is a FreeBSD security advisory.
10This is a FreeBSD problem report.
11This is a MITRE CVE identifier.
12This is a SecurityFocus Bug ID.
13This is a US-CERT security advisory.
14This is a US-CERT vulnerability note.
15This is a US-CERT Cyber Security Alert.
16This is a US-CERT Technical Cyber Security Alert.
17This is a URL to an archived posting in a mailing list. The attribute msgid is optional and may specify the message ID of the posting.
18This is a generic URL. Only it if none of the other reference categories apply.
19This is the date when the issue was disclosed (YYYY-MM-DD).
20This is the date when the entry was added (YYYY-MM-DD).
21This is the date when any information in the entry was last modified (YYYY-MM-DD). New entries must not include this field. Add it when editing an existing entry.

12.3.3. Testing Changes to the VuXML Database

This example describes a new entry for a vulnerability in the package dropbear that has been fixed in version dropbear-2013.59.

As a prerequisite, install a fresh version of security/vuxml port.

First, check whether there already is an entry for this vulnerability. If there were such an entry, it would match the previous version of the package, 2013.58:

% pkg audit dropbear-2013.58

If there is none found, add a new entry for this vulnerability.

% cd ${PORTSDIR}/security/vuxml
% make newentry

Verify its syntax and formatting:

% make validate

The previous command generates the vuln-flat.xml file. It can also be generated with:

% make vuln-flat.xml

At least one of these packages needs to be installed: textproc/libxml2, textproc/jade.

Verify that the <affected> section of the entry will match the correct packages:

% pkg audit -f ${PORTSDIR}/security/vuxml/vuln-flat.xml dropbear-2013.58

Make sure that the entry produces no spurious matches in the output.

Now check whether the right package versions are matched by the entry:

% pkg audit -f ${PORTSDIR}/security/vuxml/vuln-flat.xml dropbear-2013.58 dropbear-2013.59
dropbear-2012.58 is vulnerable:
dropbear -- exposure of sensitive information, DoS
CVE: CVE-2013-4434
CVE: CVE-2013-4421
WWW: http://portaudit.FreeBSD.org/8c9b48d1-3715-11e3-a624-00262d8b701d.html

1 problem(s) in the installed packages found.

The former version matches while the latter one does not.


All FreeBSD documents are available for download at https://download.freebsd.org/ftp/doc/

Questions that are not answered by the documentation may be sent to <freebsd-questions@FreeBSD.org>.
Send questions about this document to <freebsd-doc@FreeBSD.org>.