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How does dependency-check work?
===========
Dependency-check works by collecting information about the files it scans (using Analyzers). The information collected
is called Evidence; there are three types of evidence collected: vendor, product, and version. For instance, the
JarAnalyzer will collect information from the Manifest, pom.xml, and the package names within the JAR files scanned and
it has heuristics to place the information from the various sources into one or more buckets of evidence.
Within the NVD CVE Data (schema can be found [here](http://nvd.nist.gov/schema/nvd-cve-feed_2.0.xsd)) each CVE Entry has a list of vulnerable software:
```xml
<entry id="CVE-2012-5055">
...
<vuln:vulnerable-software-list>
<vuln:product>cpe:/a:vmware:springsource_spring_security:3.1.2</vuln:product>
<vuln:product>cpe:/a:vmware:springsource_spring_security:2.0.4</vuln:product>
<vuln:product>cpe:/a:vmware:springsource_spring_security:3.0.1</vuln:product>
```
These CPE entries are read "cpe:/[Entry Type]:[Vendor]:[Product]:[Version]:[Revision]:...". The CPE data is collected
and stored in a [Lucene Index](http://lucene.apache.org/). Dependency-check then use the Evidence collected and attempt
to match an entry from the Lucene CPE Index. If found, the CPEAnalyzer will add an Identifier to the Dependency and
subsequently to the report. Once a CPE has been identified the associated CVE entries are added to the report.
One important point about the evidence is that it is rated using different confidence levels - low, medium, high, and
highest. These confidence levels are applied to each item of evidence. When the CPE is determined it is given a confidence
level that is equal to the lowest level confidence level of evidence used during identification. If only highest confidence
evidence was used in determining the CPE then the CPE would have a highest confidence level.
Because of the way dependency-check works both false positives and false negatives may exist. Please read
(How to read the report)[thereport.html] to get a better understanding of sorting through the false positives and false
negatives.
Dependency-check does not currently use file hashes for identification. If the dependency was built from source the hash
likely will not match the "published" hash. While the evidence based mechanism currently used can also be unreliable the
design decision was to avoid maintaining a hash database of known vulnerable libraries. A future enhancement may add some
hash matching for very common well known libraries (Spring, Struts, etc.).

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How To Read The Report
========
There is a lot of information contained in the HTML version of the report. When analyzing the results, the first thing one should do is determine if the CPE looks
appropriate. Due to the way dependency-check works (see above) the report may contain false positives; these false positives are primarily on the CPE values. If the CPE value
is wrong, this is usually obvious and one should use the suppression feature in the report to generate a suppression XML file that can be used on future scans. In addition
to just looking at the CPE values in comparison to the name of the dependency - one may also consider the confidence of the CPE (as discussed in (How does dependency-check
work)[internals.html]). See the (Suppression False Positives)[suppression.html] page for more information on how to generate and use the suppression file.
Once you have weeded out any obvious false positives one can then look at the remaining entries and determine if any of the identified CVE entries are actually
exploitable in your environment. Determining if a CVE is exploitable in your environment can be tricky - for this I do not currently have any tips other then
upgrade the library if you can just to be safe. Note, some CVE entries can be fixed by either upgrading the library or changing configuration options.
One item that dependency-check flags that many may think is a false positive are old database drivers. One thing to consider about an old database driver is that the
CPE/CVEs identified are usually for the server rather then the driver. However, the presence of an old driver may indicate that you have an older version of the server
running in your environment and that server may need to be patched or upgraded. However, in some cases the old database drivers are actually unused, transitive dependencies
from other dependencies.
Regarding False Negatives
=======
As stated above, due to the nature of dependency-check there may be publicly disclosed vulnerabilities in the project dependencies scanned by dependency-check that
are not identified. With the current version of dependency-check the HTML report has a table at the top that initially displays just the dependencies with identified
vulnerabilities. This can be toggled to show all dependencies. If you examine the rows that do not have identified CPE/CVE entries you will see an "evidence count".
If the evidence count is extremely low (0-5 entries) then there may not have been enough information contained in the dependency to identify a CPE and associated CVEs.
It should be noted that while the false positives described above are bad, more concerning is that there may be vulnerabilities within the project dependencies that
have yet to be publicly known. If one has the resources consider performing security assessments on the project dependencies.