[no response] fail to adequately sanitize request strings

My client received the warning below from a security site scan. The site uses version v1.3.9h.

Are there any measures I can take to prevent this coming up as an issue?

Description:

The remote web server hosts cgi scripts that fail to adequately sanitize
request strings. By leveraging this issue, an attacker may be able
to execute arbitrary commands on the remote host.

See Also:

http://en.wikipedia.org/wiki/Code_injection
http://projects.webappsec.org/OS-Commanding

Risk Factor:

High / CVSS Base Score : 7.5 (CVSS2#AV:N/AC:L/Au:N/C:P/I:P/A:P)

Solution:

Restrict access to the vulnerable application. Contact the
vendor for a patch or upgrade.

Output:

Using the POST HTTP method, Site Scanner found that :

• The following resources may be vulnerable to arbitrary command execution :
  /index.php?main_page=contact_us&action=send [contactname=echo%20NeS%20%2
  0SuS]
  -------- output --------
  <label class="inputLabel" for="contactname">Full Name:</label>
  <input type="text" name="contactname" value="echo NeS SuS" size=" [...]
  <label class="inputLabel" for="email-address">Email Address:</label>

Other references : CWE:78, CWE:77, CWE:20, CWE:74, CWE:713, CWE:722, CWE:727, CWE:741, CWE:751, CWE:801

I really don't see how this can be considered a vulnerability.

The test string they are using consists only of normal alpha characters and encoded spaces.

Without more detail as to why they consider this a scan failure (apart from them pointing to wiki threads which bear no relation to the test they are doing ), not sure how we can help

and just to reiterate , even their test output shows no vulnerability

e.g.

<input type="text" name="contactname" value="echo NeS SuS" size=" [...]

the test string is contained within the value attribute as it should be.

Thank you for your prompt reply. I posted because I couldn't tell what the vulnerability was either. I shall post back here if more detail is provided to me.