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UPDATE:  CERT Advisory CA-2002-19 Buffer Overflows in Multiple DNS
Resolver Libraries


August 27, 2002


An important change has been made to CERT Advisory CA-2002-19.


The workaround of using a local caching DNS server is not completely
effective.  Specifically, some malicious DNS responses can be cached,
reconstructed, and passed on to systems that may have vulnerable DNS
resolver libraries.

For the most current information, including which systems are affected
and vendor statements, please see the documents listed at the end of
this message.


The following change was made to section III. of CA-2002-19:

======================================================================

III. Solution

Upgrade to a corrected version of the DNS resolver libraries

    [no change]

Use of a local caching DNS server is not an effective workaround

    When this advisory was initially published, it was thought that a
    caching DNS server that reconstructs DNS responses would prevent
    malicious code from reaching systems with vulnerable resolver
    libraries.

    This workaround is not sufficient. It does not prevent some DNS
    responses that contain malicious code from reaching clients,
    whether or not the responses are reconstructed by a local caching
    DNS server. DNS responses containing code that is capable of
    exploiting the vulnerabilities described in VU#803539 and
    VU#542971 can be cached and reconstructed before being transmitted
    to clients. Since the server may cache the responses, the
    malicious code could persist until the server's cache is purged or
    the entries expire.

    The only complete solution to this problem is to upgrade to a
    corrected version of the DNS resolver libraries as noted above.

======================================================================


The following documents have been revised:

    CERT Advisory CA-2002-19
    http://www.cert.org/advisories/CA-2002-19.html

    Vulnerability Note VU#803539
    http://www.kb.cert.org/vuls/id/803539

    Vulnerability Note VU#542971
    http://www.kb.cert.org/vuls/id/542971



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