[SECURITY-L] CAIS-Alerta: Falha do VBScript no Internet Explorer
Daniela Regina Barbetti
daniela em ccuec.unicamp.br
Seg Fev 25 11:49:04 -03 2002
----- Forwarded message from Centro de Atendimento a Incidentes de Seguranca <cais em cais.rnp.br> -----
From: Centro de Atendimento a Incidentes de Seguranca <cais em cais.rnp.br>
Subject: CAIS-Alerta: Falha do VBScript no Internet Explorer
To: <rnp-alerta em cais.rnp.br>, <rnp-seg em cais.rnp.br>
Date: Fri, 22 Feb 2002 16:04:10 -0300 (EST)
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Prezados,
O CAIS esta' repassando o alerta da Microsoft, Microsoft Security Bulletin
MS02-009, tratando de uma falha do VBScript no IE que permite o acesso a
arquivos locais atraves de paginas web.
Um atacante pode tentar explorar esta vulnerabilidade com a construcao de
uma pagina web com codigo HTML malicioso. Esta pagina web pode ser
disponibilizado em um servidor web controlado pelo atacante ou
simplesmente ser enviada para o usuario por email. Valem todas as tecnicas
de engenharia social para fazer o usuario visitar inocentemente dito
website ou para que ele leia o e-mail com conteudo malicioso.
. A vulnerabilidade somente permite a leitura de arquivos. Nao
pode ser utilizada para cirar, remover, modificar ou executar
arquivos.
. A vulnerabilidade somente permite que um atacante leia arquivos
que podem ser abertos por um navegador, como imagens, arquivos
html e arquivos texto. Arquivos do Word nao podem ser abertos.
. O atacante necessita especificar o nome e a localizacao dos
arquivos para que possam ser abertos.
. O ataque utilizando email sera' impedido se o usuario estiver
utilizando algum dos seguintes produtos: Outlook 98 ou 2000 com
o Outlook Email Security Update instalado; Outlook 2002; ou
Outlook Express 6.
Sistemas Afetados:
. Microsoft Internet Explorer 5.01
. Microsoft Internet Explorer 5.5
. Microsoft Internet Explorer 6.0
Correcoes disponiveis:
. http://www.microsoft.com/Windowsupdate
Identificador do CVE:
CAN-2002-0052 (http://cve.mitre.org)
Maiores informacoes:
http://www.microsoft.com/technet/security/bulletin/MS02-009.asp
O CAIS recomenda fortemente aos administradores de sistemas Windows que
atualizem seus sistemas em virtude da gravidade desta vulnerabilidade.
Atenciosamente,
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- ----------------------------------------------------------------------
Title: Incorrect VBScript Handling in IE can Allow Web Pages to
Read Local Files
Date: 21 February 2002
Software: Internet Explorer
Impact: Information Disclosure
Max Risk: Critical
Bulletin: MS02-009
Microsoft encourages customers to review the Security Bulletin at:
http://www.microsoft.com/technet/security/bulletin/MS02-009.asp.
- -
- ----------------------------------------------------------------------
Issue:
======
Frames are used in Internet Explorer to provide for a fuller
browsing experience. By design, scripts in the frame of one site or
domain should be prohibited from accessing the content of frames
in another site or domain. However, a flaw exists in how VBScript
is handled in IE relating to validating cross-domain access. This
flaw can allow scripts of one domain to access the contents of
another domain in a frame.
A malicious user could exploit this vulnerability by using
scripting to extract the contents of frames in other domains,
then sending that content back to their web site. This would
enable the attacker to view files on the user's local machine
or capture the contents of third-party web sites the user visited
after leaving the attacker's site. The latter scenario could,
in the worst case, enable the attacker to learn personal
information like user names, passwords, or credit card information.
In both cases, the user would either have to go to a site under
the attacker's control or view an HTML email sent by the attacker.
In addition, the attacker would have to know the exact name and
location of any files on the user's system. Further, the attacker
could only gain access to files that can be displayed in a browser
window, such as text files, HTML files, or image files.
Mitigating Factors:
====================
- The vulnerability could only be used to view files. It could not
be used to create, delete, modify or execute them.
- The vulnerability would only allow an attacker to read files that
can be opened in a browser window, such as image files, HTML
files and text files. Other file types, such as binary files,
executable files, Word documents, and so forth, could not be read.
- The attacker would need to specify the exact name and location of
the file in order to read it.
- The email-borne attack scenario would be blocked if the user were
using any of the following: Outlook 98 or 2000 with the Outlook
Email Security Update installed; Outlook 2002; or Outlook
Express 6.
Risk Rating:
============
- Internet systems: Moderate
- Intranet systems: Moderate
- Client systems: Critical
Patch Availability:
===================
- A patch is available to fix this vulnerability. Please read the
Security Bulletin at
http://www.microsoft.com/technet/security/bulletin/ms02-009.asp
for information on obtaining this patch.
Acknowledgment:
===============
- Zentai Peter Aron, Ivy Hungary Ltd (http://w3.ivy.hu/)
- -
- ---------------------------------------------------------------------
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