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Home » Security Advisories» FreeBSD » FreeBSD-SA-02:16-GIF/JPEG comment vulnerability in Netscape

FreeBSD-SA-02:16-GIF/JPEG comment vulnerability in Netscape

The GIF89a and JPEG standards permit images to have embedded comments, in which any kind of textual data may be stored. Versions 4.76 and earlier of the Netscape browser will execute JavaScript contained in such a comment block, if execution of JavaScript is enabled in the configuration of the browser.

  • Vendor: FreeBSD
  • Vendor ID: SA-02:16
  • Date: March 12, 2002

The Netscape browser supports a non-standard URL scheme, `about:'.
Visiting `about:' URLs causes Navigator to display information which
may be sensitive. For example, `about:global' gives a listing of
recently accessed URLs; `about:cache' shows a similar listing, but
with the time each page was visited and the name of each corresponding
file in the disk cache; and `about:config' displays the full
configuration of the browser.

JavaScript executed from the comment block of a maliciously
constructed image can send information from an `about:' URL back to a
hostile Web server.

The Netscape ports are not installed by default, nor are they "part of
FreeBSD" as such: they are part of the FreeBSD ports collection, which
contains thousands of third-party applications in a ready-to-install
format. The ports collection shipped with FreeBSD 4.5 contains some
Netscape versions which are vulnerable to these problems.

FreeBSD makes no claim about the security of these third-party
applications, although an effort is underway to provide a security audit
of the most security-critical ports.

III. Impact

The browser can be caused to transmit sensitive information to a
hostile Web server, if JavaScript is enabled and a page on the server
is visited.

If you have not chosen to install a Netscape port or package, your
system is not vulnerable to this problem.

IV. Workarounds

Do one of the following:

1) Deinstall affected Netscape ports or packages, if any are installed.

2) Disable JavaScript. This can be done interactively by running
Navigator, going to the Edit menu, choosing Preferences, and changing the
setting in the Advanced section.

Alternatively, append the line:

user_pref("javascript.enabled", false);

to the $HOME/.netscape/preferences.js of every user. Users are likely
to want to re-enable JavaScript, because its use is required by some
Web sites. If they do, they could become vulnerable again.

3) Similarly, disable automatic loading of images. The corresponding
configuration line is:

user_pref("general.always_load_images", false);

Some Web sites require images. If users enable automatic loading, or
if they click the Images button, they could become vulnerable again.

4) Install a filtering proxy, and configure it to block all images
from untrusted sites. The www/adzap or www/adzapper ports may be
suitable. Doing this will make many Web sites unviewable.

V. Solution

One of the following:

1) Upgrade your entire ports collection and rebuild the relevant Netscape
port, if available. Netscape binaries for several platforms, including
FreeBSD/i386, were discontinued before the release of 4.77.

2) Deinstall the old package and install a new package, obtained from the
following directories:



3) Download a new port skeleton for the Netscape port from:

and use it to rebuild the port.

NOTE: Since there are so many variations of the Netscape ports in the
FreeBSD ports collection they are not listed separately
here. Localized versions are also available in the respective language

4) Use the portcheckout utility to automate option (3) above. The
portcheckout port is available in /usr/ports/devel/portcheckout or the
package can be obtained from:

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