dns_diagnostics.php SPF DNS lookup loop

[ualnwe]

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Description

The problem:

When using dns diagnostics to check SPF records, a possible loop can occur. If the domain has an SPF record pointing to another domain that has an SPF record referencing the original via include:. This causes an infinite stall.

Example:

• call dns_diagnostics.php?domain=example.com
• example.com has an SPF record with include:mail.example.com
• mail.example.com has an SPF record with include:example.com

Line 50 of data/web/inc/spf.inc.php only checks for the current domain $check_domain != $domain but the function below passes in the currently checking domain without context of what originally called it, so a loop occurs in this case.

I understand in this situation, technically the SPF records may be at fault/invalid, but I found this bug while moving an existing mail system over to mailcow that had been working this way for years, and so may cause frustration to troubleshoot for others in a similar situation.

There are no logs generated (or needed) for this action as it simply keeps looping forever, stalling the current php-fpm session, at least on my system.

The fix:

I appended , $orig_domain = "" to the get_spf_allowed_hosts(.. function in data/web/inc/spf.inc.php and also set every call within spf.inc.php to pass $check_domain to this new argument. Then by adding an additional check on line 50 for this original domain && $orig_domain != $domain it correctly stops after one loop as we're back on the original domain.

~~I may open a pull request for the fix, but it's a hacky workaround and am not sure if it handles edge cases or effects anything else.~~ Opened #4716 Any better way to solve this is welcome.

Thank you!

Logs

N/A

Steps to reproduce

• example.com has an SPF record with include:mail.example.com
• mail.example.com has an SPF record with include:example.com
• call dns_diagnostics.php?domain=example.com
• It will hang indefinitely

System information

N/A