Overly permissive SPF configurations refer to settings that are set so loosely and broadly that anyone on the Internet can send emails from your domain. These configurations weaken your email infrastructure, ultimately exposing your brand name to phishing, spoofing, ransomware attacks, and other security risks.
If unauthorized, malicious people send emails from your domain and such emails aren’t flagged, don’t you think your domain’s reputation will be questioned? Your domain can also be subjected to blocklisting, disrupting genuine communication exchanges. Not only this, but overly permissive SPF configurations create issues in the working of DKIM and DMARC.
And we don’t need to mention how organizations falling under regulations like GDPR, HIPAA, or PCI-DSS can have legal and financial consequences awaiting them because of weak email security.
To keep such problems away, ensure your SPF record does not have the following configurations.
Common overly permissive SPF settings
Here’s a comprehensive list of overly permissive SPF configurations, along with detailed explanations of why each poses a risk to a company’s domain reputation and operations:
1. +all mechanism
Using the ‘+all’ mechanism allows any server to send emails on behalf of your domain. Threat actors are on the lookout for such vulnerable settings to launch spam and phishing campaigns. What’s worse, this can impact the delivery of legitimate emails, and they can get flagged as spam because the broad permission negates the authenticity provided by SPF.
2. Use of wide IP ranges
Including wide IP ranges in your SPF record is problematic because thousands of IPs will be authorized. Many of these will not belong to your company or trusted users. This way, threat actors within the allowed range will get the opportunity to exploit your reputed domain for spam or phishing.
Also, filtering the illegitimate IPs would be very challenging or sometimes impossible. When you broadly and loosely authorize senders, your ability to detect malicious IPs dilutes.
3. Not specifying the ‘all’ mechanism
The ‘all’ mechanism has to be paired with either ‘~’ or ‘-’ otherwise, it remains ambiguous, which leaves room for interpretation. Since no action is specified, there will be major inconsistencies in the way emails are handled by different receiving servers. This will open a backdoor for spammers, as there is no clear rejection policy for senders who aren’t officially authorized by you to send emails from your domain.
4. Excessive wildcarding
Let’s understand this through an example-
v=spf1 a:*.example.com ~all
This is considered a misconfiguration because the above example matches all subdomains of example.com, including the ones that won’t be used for sending emails. This way, unauthorized domains can be used for sending emails, creating ambiguity in email routing.
5. Mixing too many mechanisms
When you mix multiple mechanisms, like ‘ip4,’ ‘ip6,’ ‘include,’ ‘mx,’ and ‘ptr,’ the SPF record becomes complex and erupts inefficiencies in operations. This complexity increases the likelihood of misconfigurations, making it easier to inadvertently authorize untrusted sources.
Additionally, SPF has a strict limit of 10 DNS lookups during validation; combining multiple mechanisms often risks exceeding this limit. When the limit is breached, mail servers may disregard the entire SPF record, effectively leaving the domain unprotected and vulnerable to spoofing. This not only undermines the domain’s email security but also risks damaging its reputation due to unauthorized or malicious email activities.
6. Not removing deprecated or unused entries
If any entries are no longer used for sending emails, you must remove them from your SPF record. Including obsolete or unused entries increases the attack surface unnecessarily. Moreover, it’s hard to manage so many entries; the shorter the SPF record, the easier it is to understand the legitimate email flow and fix issues.
7. Overuse of the ‘include’ mechanism
Example- v=spf1 include:example1.com include:example2.com include:example3.com ~all
Using too many ‘include’ statements, as shown in the example, makes an SPF record complex and increases the chances of errors because multiple third parties get involved. If any of the domains is misconfigured or gets compromised, your domain can also take a toll and be implicated in malicious cyber activities.
You can also expect that your SPF record may exceed the DNS lookup limit of 10, which crashes the entire SPF protocol. If your SPF record is facing this issue, use our automatic SPF flattener or contact us for assistance.
