Cisco Security Advisory-
The Cisco Content Service Switch (CSS) 11000 and 11500 series switches respond to certain Domain Name Service (DNS) name server record requests with an error code and no Start of Authority (SOA) records, which can be negatively cached by some DNS name servers resulting in a potential denial-of-service attack for a particular domain name hosted by a CSS. To be affected by this vulnerability, CSS devices must be configured for Global Server Load Balancing. The CERT/CC issued a vulnerability note on this issue (VU#714121). Cisco is providing repaired software, and customers are urged to upgrade to repaired code.
This vulnerability in CSS is documented as Cisco Bug IDs CSCdz62499 and CSCea36989.
This advisory will be available at https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20030430-dns.
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Vulnerable Products
The CSS 11000 and 11500 series switches (formerly known as Arrowpoint) consist of the CSS 11050, CSS 11150, CSS 11800 11501, 11503, and 11506 hardware platforms. They run the Cisco WebNS software.
CSS 11000 and 11500 series switches running any WebNS software revision are affected by this vulnerability only if they are configured for Global Server Load Balancing (also known as DNS Load Balancing).
To determine if your CSS equipment is configured for Global Server Load Balancing, please check the configuration for the dns-server command. If this command is not present, the configuration is not vulnerable to this issue.
Products Confirmed Not Vulnerable
No other Cisco products are currently known to be affected by this vulnerability.
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Commonly, the name service in use by the Internet, DNS, uses various record types for queries between DNS servers and clients. The common record types are Address records (A-records), Name Server records (NS records), Mail Exchange (MX records), Start of Authority records (SOA records), and Canonical Name records (CNAME records). Each record or query type has various rules and formats associated with it, including details about what may be cached, what may be trusted by other clients, etc.
Clients usually send queries to a local server, and that local server may send further queries to other servers on behalf of that client in order to formulate a response for the client. When the local server receives the responses, it will cache the information for future use and will respond to the client.
The CSS 11000 and 11500 series switches have the ability to act as an authoritative DNS name server and will only respond to DNS A-record requests. If a CSS configured for DNS via the Global Server Load Balancing feature receives a DNS request or query for an unsupported record type, the CSS will respond with rcode 4 "not implemented" or rcode 3 "NXDOMAIN," depending on the version of WebNS. When an NXDOMAIN response code is received, the querying server will typically stop attempting to resolve any other record type for that name. For example, an NXDOMAIN response to the AAAA query may stop the server from sending an A query, though there may indeed be an A-record in existence. Some resolvers that receive an NXDOMAIN response and support negative caching will not query for A-records for the same name until the negatively cached error response has expired, which can take an extended period of time.
When the DNS query received is for a legitimate host name but an unsupported record type, these negative responses may be cached by various proxies or caching nameservers and will lead to apparent temporary service outages when other clients query the caching nameserver or proxy for the legitimate host name. Though network services are physically unaffected, end users are dependent upon name resolution, and the lack of correct DNS information can result in effective service outages.
Cisco Bug ID CSCdz62499 was the first fix, which changed the response from rcode 3 to rcode 4. This result code is also negatively cached, so the complete fix has been correctly addressed with Cisco Bug ID CSCea36989.
The CSS will now return an RFC 2308-compliant NODATA type 3 response, which is an authoritative answer with rcode=NOERROR, answer=0, and no SOA. This response should cause the specific client to query for another A-record instead of continuing to query for the unsupported record type or using the negatively cached error message or NXDOMAIN answer.
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The workaround for this issue is to disable Global Server Load Balancing and to configure DNS records for the affected servers and domains on a separate compliant DNS server until an upgrade to repaired versions can be installed.
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The following table summarizes the CSS software releases affected by the defect described in this notice and provides scheduled dates on which the earliest corresponding fixed releases will be available. Dates are tentative and subject to change.
When selecting a release, keep in mind the following definitions.
- A maintenance release is the most heavily tested and highly recommended release.
- An interim release has much less testing than a maintenance release and should be selected only if no other suitable release fixes the defect.
In all cases, customers should exercise caution to be certain the devices to be upgraded contain sufficient memory and that current hardware and software configurations will continue to be supported properly by the new release.
Affected Version
Fixed Version
Estimated Date Available
5.00 up to and including 5.00.1.05
- 5.00 build 105 (ap0500105.adi-gz)
5.00.1.08S - Interim Build
- 5.00 build 108s (ap0500108s.adi-gz)
2003-Apr-29
5.00.2.01 - Maintenance Release
- 5.00 build 201 (ap0500201.adi-gz)
2003-May-30
5.01, 5.02, and 5.03
Upgrade to 6.10 - Maintenance Release
2003-May-15
7.10 up to and including 7.10.1.02
- 7.10 build 102 (sg0710102.adi-gz)
7.20.0.03 - Maintenance Release
- 7.20 build 003 (sg0720002.adi-gz)
Available Now
7.10.2.06 - Maintenance Release
- 7.10 build 206 (sg0710206.adi-gz)
Available Now
Note: Bullet items in the table above provide information on build identifier and file name (previous naming convention for the same build).
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This vulnerability has been published by the CERT at http://www.kb.cert.org/vuls/id/714121
. CERT notes that this
issue is not new. The Cisco PSIRT is not aware of any malicious use of the
vulnerabilities described in this advisory, but because of the nature of this
issue, it may be unlikely that exploitation would be noticed or
reported.
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To learn about Cisco security vulnerability disclosure policies and publications, see the Security Vulnerability Policy. This document also contains instructions for obtaining fixed software and receiving security vulnerability information from Cisco.
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Show LessRevision 1.0
2003-April-30
Initial public release.
Revision 1.1
2003-May-01
Alternate build identifiers added for clarification in Software Versions and Fixes.
Revision 1.2
2003-May-23
Edited Affected Version column contents in the table to clarify version numbers.
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