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DNS cache pollution, also known as DNS cache poisoning, occurs when attackers trick DNS resolvers into caching false information, resulting in users being directed to the wrong websites. This is possible because DNS servers use UDP instead of TCP, and because there is currently no verification for DNS information. To prevent this, DNS servers can enable the Secure Cache Against Pollution setting, which allows the DNS server to protect its cache against referrals that are potentially polluting or non-secure. When this setting is enabled, the DNS server ignores DNS resource records that come from servers that are not authoritative for them. While this may cause extra DNS queries, the security benefits are significant, making it highly recommended.
| Characteristics | Values |
|---|---|
| Definition | Secure Cache Against Pollution (SCAP) is a set of techniques used to protect a cache from becoming polluted or overloaded with outdated or invalid entries. |
| Mechanism | When the setting is enabled, the server caches only those records with a name that corresponds to the domain for which the original queried name was made. Any referrals received from another DNS server along with a query response are simply discarded. |
| Use Cases | This setting helps prevent unauthorized computers from impersonating another network server. |
| Implementation | In Server options, select the Secure cache against pollution check box, and then click OK. To open DNS Manager, click Start, point to Administrative Tools, and then click DNS. |
| Microsoft Windows | DNS cache pollution protection is enabled by default in Microsoft Windows 2003. |
| Microsoft Windows 2000 | To enable DNS cache pollution protection, start the Registry Editor (Regedt32.exe). |
| Microsoft DNS Server | The Secure Cache Against Pollution setting allows the DNS server to ignore DNS resource records that come from servers that are not authoritative for them. |
| Drawbacks | Enabling this setting can cause extra DNS queries, resulting in slower times. |
| Alternatives | A more secure DNS protocol called DNSSEC (Domain Name System Security Extensions) aims to verify DNS data integrity and origin using public key cryptography. |
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What You'll Learn
DNS cache poisoning
DNS servers translate human-readable website addresses like 'cloudflare.com' into machine-readable IP addresses. When a user attempts to navigate to a website, their operating system sends a request to a DNS resolver, which responds with the IP address. The web browser then takes this address and initiates loading the website. DNS resolvers will save responses to IP address queries for a certain amount of time, allowing them to respond to future queries more quickly.
Attackers can poison a DNS cache by impersonating DNS nameservers, making a request to a DNS resolver, and then forging the reply when the DNS resolver queries a nameserver. This is possible because there is no verification for DNS information, and DNS servers use UDP, which does not require a 'handshake' to initiate communication. Additionally, attackers must know or guess certain factors to carry out a successful attack, such as which DNS queries are not cached by the targeted DNS resolver.
To prevent DNS cache poisoning, organizations can adopt DNSSEC (Domain Name System Security Extensions), which uses public key cryptography to verify and authenticate data. DNSSEC extensions were published in 2005, but they are not yet mainstream, leaving DNS vulnerable to attacks. Other methods to prevent DNS cache poisoning include using a fast and DoS-resistant DNS resolver and regularly updating and patching DNS software.
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DNS spoofing
DNS cache poisoning, also known as DNS spoofing, is a type of cyber attack that involves manipulating DNS records to redirect users to a fraudulent website. This attack takes advantage of flaws in the DNS software and its associated protocols. By exploiting these vulnerabilities, an attacker can deceive users into accepting content from a non-authentic server, ultimately tricking them into downloading malicious content such as computer worms or viruses. This can also enable attackers to steal sensitive data from unsuspecting users.
To execute a DNS spoofing attack, an attacker must force the target DNS server to make a request for a domain controlled by one of the attacker's name servers. They can accomplish this by using methods such as social engineering or exploiting weaknesses in the DNS server software. Once the attacker has intercepted the communication channel between the client and the server computer, they can employ tools like arpspoof to deceive the client into believing that the server IP address belongs to the attacker.
The impact of DNS cache poisoning goes beyond the immediate effects of redirecting web traffic. It exposes users to further risks, including phishing, malware injections, denial of service, and website hijacking. Additionally, attackers can increase the authority and search ranking of their fraudulent websites, attracting more unsuspecting users in the future.
To defend against DNS spoofing attacks, a more secure DNS protocol called DNSSEC (Domain Name System Security Extensions) has been introduced. DNSSEC provides origin authentication, data integrity, and authenticated denial of existence for DNS data. However, despite its availability since 2005, DNSSEC has not yet gained mainstream adoption, leaving DNS vulnerable to attacks.
Another way to protect against DNS spoofing is to use trustworthy DNS servers with highly secure and regularly updated systems. Cryptographically securing communication with DNS servers using protocols like DNSCrypt ensures that responses originate from a trusted source and have not been tampered with. Additionally, keeping DNS software up-to-date with the latest security patches can help prevent many types of attacks.
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Secure Cache Against Pollution (SCAP)
SCAP helps prevent this issue by allowing the DNS server to protect its cache against potentially polluting or non-secure referrals. When the setting is enabled, the server only caches records with names corresponding to the domain for which the original query was made. Any referrals received from another DNS server, along with the query response, are discarded. For example, if a query is made for example.microsoft.com, and a referral answer provides a record for a name outside the microsoft.com domain name tree (such as msn.com), that name is discarded with SCAP enabled.
SCAP can be enabled through the Server options by selecting the "'Secure cache against pollution' check box" and clicking OK. This setting is highly recommended, as the security benefits outweigh the cost of potential extra DNS queries. While SCAP helps protect against DNS cache pollution, it is important to note that DNS cache pollution protection is not enabled by default in all software versions, and authority can be easy to fake if the upstream DNS server has been compromised.
Additionally, other measures are being developed to address DNS cache pollution. A more secure DNS protocol called DNSSEC (Domain Name System Security Extensions) aims to verify DNS data integrity and origin using public-key cryptography. However, DNSSEC has not yet been widely adopted, leaving DNS vulnerable to attacks.
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DNSSEC
DNS cache pollution, or DNS cache poisoning, occurs when attackers trick DNS resolvers into caching false information, resulting in users being directed to the wrong websites. This is possible because there is typically no way for DNS resolvers to verify the data in their caches, and because DNS servers use UDP instead of TCP.
To enable DNSSEC, a zone operator creates digital signatures for each RRset using the private ZSK and stores them in their name server as RRSIG records. The zone operator also needs to make their public ZSK available by adding it to their name server in a DNSKEY record. When a DNSSEC resolver requests a particular record type, the name server returns the corresponding RRSIG. The resolver can then pull the DNSKEY record containing the public ZSK from the name server.
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DNS cache pollution protection
DNS cache pollution, also known as DNS poisoning or DNS spoofing, is a type of attack where a malicious actor corrupts the DNS cache of a server or client. This allows the attacker to redirect traffic intended for legitimate websites to fraudulent or malicious websites. When a user attempts to access a website, the compromised DNS resolver provides a fake IP address, directing the user to a malicious server. The attacker aims to trick users into providing sensitive information, downloading malware, or enabling other types of cyberattacks such as man-in-the-middle attacks.
To prevent DNS cache pollution, it is recommended to enable the "Secure Cache Against Pollution" setting. This setting causes the DNS server to ignore DNS resource records that originate from non-authoritative servers. While this may result in additional DNS queries, the enhanced security makes it worthwhile. Microsoft Windows 2003 and later versions have this setting enabled by default, which can be confirmed by accessing the DNS Management Console and checking the Advanced tab.
Another effective method to protect against DNS cache pollution is to employ DNSSEC (Domain Name System Security Extensions). DNSSEC uses public-key cryptography to verify and authenticate DNS data, ensuring its integrity and legitimacy. It applies cryptographic validations to DNS records, preventing attacks like cache pollution and spoofing. While DNSSEC extensions were published in 2005, they have not yet been widely adopted, leaving DNS vulnerable to attacks.
Additionally, it is crucial to keep DNS servers and network infrastructure updated with the latest security patches. Vendors regularly release updates that address vulnerabilities exploited in DNS cache pollution attacks. Implementing a DNS Firewall is also beneficial, as it filters and monitors DNS queries, blocking suspicious or unauthorized requests. This ensures that only legitimate DNS queries and responses are processed, providing added protection against eavesdropping or manipulation of DNS responses.
Furthermore, using a centralized, automated DNS solution like BlueCat can simplify the process of protecting against DNS cache pollution. BlueCat's platform allows for easy comparison between DNS requests and responses, helping identify potential discrepancies. Adjusting the TTL (Time to Live) of DNS caching servers can also mitigate the impact of DNS cache pollution issues by naturally decreasing the number of queries that could be led to the wrong address.
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Frequently asked questions
DNS cache pollution, also known as DNS cache poisoning, is when false information is entered into a DNS cache, causing DNS queries to return an incorrect response and users to be directed to the wrong websites.
To enable secure cache against pollution, you can go into your Server options and select the "Secure cache against pollution" check box. On Windows 2000, you can also enable this feature by starting the Registry Editor (Regedt32.exe).
Enabling secure cache against pollution helps protect your cache from becoming overloaded with outdated or invalid entries. It also helps prevent unauthorized computers from impersonating another network server.
