DNS | TXT records

The Domain Name System (DNS) is more than just a directory service that converts human-friendly domain names to IP addresses—it’s a critical infrastructure that underpins the fabric of the internet, facilitating user access and communication across the globe.

The TXT records are versatile cornerstone among the DNS record types. Originally designed for human-readable text in a DNS record, TXT records have evolved beyond their original intentions into tools supporting many other functions.

Understanding these DNS records is a requisite for experts who design, manage and secure domain name operations. Let’s discuss text records, decoding their structure, applications and underlying impact on the DNS infrastructure.

What is a TXT record?

A TXT record is a DNS record that stores text information for sources outside your domain to verify site ownership or implement email security measures such as SPF, DKIM and DMARC. The TXT record is peculiar due to its simplicity and versatility. Its structure is straightforward: It consists of a freely defined text string that can be utilized for various purposes.

According to the technical specifications outlined in RFC 1035, the text record was initially introduced to store descriptive notes about a host or associate human-readable information with a domain. Today, this type of DNS record has significantly evolved. It serves pivotal roles in security, verification and control protocols for the internet. This evolution is driven by the record’s ability to store data formatted according to different specifications, making it a versatile tool for implementing protocol validations.

What are the functions of text records?

Today, TXT records perform numerous critical roles beyond mere annotation. They are instrumental in enhancing internet security, verifying domain ownership, providing critical infrastructure information and implementing policy frameworks.

1 Email security

One of the most prominent uses is email security, where TXT records are critical for email protocols. These records verify that email messages are not forged, reducing spam and phishing attacks. For instance, major email providers like Google and Microsoft leverage these to authenticate email sources, significantly curtailing email spoofing.

2 Spam prevention

Text records in DNS support anti-spam protocols like SPF, DKIM and DMARC, verifying sender authenticity and integrity to prevent malicious email spoofing. SPF allows domain owners to define which mail servers can send emails on their behalf, while DKIM provides a way to validate a message’s digital signature. DMARC uses policies to advise email recipients on handling messages failing SPF or DKIM checks, often leading to rejecting or flagging such emails as spam.

3 Domain ownership

Additionally, TXT records are used to verify domain ownership for services like Google Search Console and SSL certificate issuers. Domain holders can prove ownership by adding a specific text record without altering visible website content, streamlining service integrations and security validations.

4 Internet policy

They are also employed in implementing site-wide policies, such as the HSTS (HTTP Strict Transport Security) policy, which enhances web security by enforcing strict HTTPS use, reducing the risk of man-in-the-middle attacks. A case in point is the adoption of HSTS policy declarations via TXT records by leading e-commerce platforms to secure customer transactions and data.

5 Infrastructure roles

Furthermore, TXT records serve in diverse infrastructure roles, including delineating server information for VPN configuration or detailing service-related records within an organization. Thus, they act as versatile tools in network management and service discovery.

These varied functions and real-world applications underscore the adaptability and essential nature of text records within today’s DNS and the broader internet ecosystem, highlighting their evolved role from simple annotations to foundational security and infrastructure components.

Best practices for TXT record management

Adhering to best practices when managing TXT records is essential for maintaining a well-organized and secure domain infrastructure.

If applicable, domain administrators should maintain clear documentation of all TXT records, including their purposes and expiry dates. Regular audits help identify outdated or unnecessary records that might compromise security or clutter the DNS configuration. It’s also wise to segment records by service or policy type and use descriptive labels for easier identification and management.

Security considerations for TXT records

While versatile in function, TXT records present certain security considerations that must be factored into their utilization to prevent vulnerabilities.

One major risk is the exposure of sensitive information. Since TXT records are publicly accessible, storing sensitive data, such as security or administrative details, presents a potential exploit vector for malicious actors who could use this information to craft targeted attacks. Another risk involves using TXT records for phishing or spamming, where attackers set up authentic-looking records to deceive users or email systems.

Exposure of sensitive information: TXT records are publicly accessible, making any sensitive information stored in them visible to anyone performing a DNS lookup. This exposure can include security tokens, verification codes, or internal network details.

Lack of access control: There is no built-in mechanism to restrict who can view TXT records. Once the information is in a TXT record, it is accessible worldwide.

Increased attack surface: By revealing sensitive information, attackers can gain insights into internal systems, configurations or operational details that could be exploited.

Mitigation measures:

-> Limit the use of sensitive information in TXT records.

-> Employ alternative methods for validation and configuration that do not expose sensitive data.

-> Regular audits of DNS records to ensure that no sensitive information is inadvertently exposed.

To mitigate these vulnerabilities, carefully considering what information is published in TXT records is crucial. Organizations should avoid using text records to store confidential or detailed operational data. Instead, referencing indirect identifiers or employing obfuscation techniques where possible could reduce the direct value of the TXT record data to an attacker.

Managing TXT records comes with inherent size limitations. The DNS protocol restricts individual TXT records to 255 characters and while an entire record can exceed this limit, it must be segmented into smaller strings concatenated during processing. Administrators may fragment the data across multiple strings within a single record or use multiple text records if appropriate to handle more extensive data requirements. Alternative verification or policy communication methods, such as CNAME records or web-based verification, might offer a viable workaround for large data sets that can’t be neatly split.

Deep dive into TXT record role in email security

TXT records play a critical role in email infrastructure. By allowing for the implementation of protocols, they serve as the foundation for securing email communication and fighting spam and phishing attacks. This deep dive into their role will explore how these TXT DNS records contribute to the integrity and trustworthiness of email exchanges.

-> SPF and email authentication

Sender Policy Framework (SPF) is a security measure that prevents email spoofing. SPF uses TXT records within the DNS to list the mail servers authorized to send emails on behalf of a domain. When an email is received, the recipient’s server checks the SPF record by looking up the text record for the sender’s domain. If the sending server is not listed in the SPF record, the email can be flagged or rejected, significantly reducing the likelihood of successful spoofing.

-> DKIM and email integrity

DomainKeys Identified Mail (DKIM) is another email authentication method that uses cryptographic signatures to verify that an email message was not altered during transmission. DKIM achieves this by allowing the sending domain to attach a digital signature to outgoing emails encoded in a TXT record in the domain’s DNS. Recipient servers can then retrieve the DKIM TXT record, use it to decode the message’s signature and confirm its authenticity and integrity.

-> DMARC and email authenticity

Domain-based Message Authentication, Reporting and Conformance (DMARC) is a protocol that uses SPF and DKIM records to assess an email’s authenticity and defines actions to take if it fails these checks. DMARC policies are published in the DNS as text records, allowing domain holders to specify how their emails should be handled by recipient servers if authentication by SPF and DKIM fails.

The future of text records

The future of TXT records appears promising, with potential for innovative applications and the evolution of new standards. As internet security and digital identity verification become increasingly pivotal, TXT records will likely evolve from their traditional roles. We may witness enhanced encryption standards for TXT records or the development of new DNS-based authentication methods that leverage TXT records for more secure communication between services.

Furthermore, as the Internet of Things (IoT) and blockchain technologies mature, TXT records could play a crucial role in decentralized networks by providing a means for verifying device identity or facilitating smart contracts without centralized control. The flexibility of text records makes them an attractive tool for various future applications, including but not limited to more nuanced and secure methods of domain verification, implementation of complex network policies and innovative approaches to digital identity management.

TXT records vital components in DNS management

TXT records play an indispensable role within the DNS ecosystem, serving various purposes beyond their original design. These DNS records have proven their versatility and importance, from facilitating email security protocols like SPF and DMARC to verifying domain ownership and implementing web security policies like HSTS.

If you need assistance setting up your DNS records or have specific inquiries about TXT records, please contact our Partner Success Managers.

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