[GH-ISSUE #3996] validateDomain() is too strict #8211

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saavagebueno · 2026-08-05T01:16:51-04:00

saavagebueno commented

2026-08-05 01:16:51 -04:00

Originally created by @zvpunry on GitHub (Jun 17, 2025).
Original GitHub issue: https://github.com/netbirdio/netbird/issues/3996

The domainPattern regex in management/server/nameserver.go is too strict, it doesn't allow labels that are completely valid according to rfc1035. As an example, it forbids labels like "x", "x1, "x--x" as tld and possibly some more.

The validateDomain() function must allow rfc1035 labels. The easiest fix is to remove the regex and just depend on dns.IsDomainName() which is not very strict.

If some additional validation is needed, it must allow rfc1035 labels. But maybe even rfc1035 is too strict: See https://www.rfc-editor.org/rfc/rfc2181#section-11

Originally created by @zvpunry on GitHub (Jun 17, 2025). Original GitHub issue: https://github.com/netbirdio/netbird/issues/3996 The domainPattern regex in management/server/nameserver.go is too strict, it doesn't allow labels that are completely valid according to rfc1035. As an example, it forbids labels like "x", "x1, "x--x" as tld and possibly some more. The validateDomain() function must allow rfc1035 labels. The easiest fix is to remove the regex and just depend on dns.IsDomainName() which is not very strict. If some additional validation is needed, it must allow rfc1035 labels. But maybe even rfc1035 is too strict: See https://www.rfc-editor.org/rfc/rfc2181#section-11

saavagebueno added the feature-request dns labels 2026-08-05 01:16:51 -04:00

saavagebueno closed this issue

2026-08-05 01:16:52 -04:00

saavagebueno commented

2026-08-05 01:16:52 -04:00

@zvpunry commented on GitHub (Jun 17, 2025):

There is also https://www.rfc-editor.org/rfc/rfc1123#section-2 which references the syntax from rfc952 (which is the same as rfc1035) but also allows a label to start with a digit. A regex to validate such a name would be ^(([a-zA-Z0-9]|[a-zA-Z0-9][a-zA-Z0-9-]*[a-zA-Z0-9])\.?)+$ https://regex101.com/r/GXfv3m/1

I mentioned rfc2181 earlier, it basically says everything can be used as a label but it must be limited to 63 bytes and the whole domainname must fit into 255 bytes, which is enforced by dns.IsDomainName().

@zvpunry commented on GitHub (Jun 17, 2025): There is also https://www.rfc-editor.org/rfc/rfc1123#section-2 which references the syntax from rfc952 (which is the same as rfc1035) but also allows a label to start with a digit. A regex to validate such a name would be `^(([a-zA-Z0-9]|[a-zA-Z0-9][a-zA-Z0-9-]*[a-zA-Z0-9])\.?)+$` https://regex101.com/r/GXfv3m/1 I mentioned [rfc2181](https://www.rfc-editor.org/rfc/rfc2181#section-11) earlier, it basically says everything can be used as a label but it must be limited to 63 bytes and the whole domainname must fit into 255 bytes, which is enforced by dns.IsDomainName().

saavagebueno commented

2026-08-05 01:16:52 -04:00

@zvpunry commented on GitHub (Jan 4, 2026):

This screenshot should make it more clear where my problem is. When adding or modifying a DNS Server, it isn't possible to add a list of Match Domains (i.e. "intranet" and "intranet2").

I use my own patch (see pull request #4000) that just removes the too strict tests without a problem.

@zvpunry commented on GitHub (Jan 4, 2026): <img width="576" height="643" alt="Image" src="https://github.com/user-attachments/assets/d5f8b382-93b2-478f-ac60-3e9a5aa5993d" /> This screenshot should make it more clear where my problem is. When adding or modifying a DNS Server, it isn't possible to add a list of Match Domains (i.e. "intranet" and "intranet2"). I use my own patch (see pull request #4000) that just removes the too strict tests without a problem.

saavagebueno commented

2026-08-05 01:16:52 -04:00

@zvpunry commented on GitHub (Jan 29, 2026):

Fixed by https://github.com/netbirdio/netbird/pull/5211

@zvpunry commented on GitHub (Jan 29, 2026): Fixed by https://github.com/netbirdio/netbird/pull/5211

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Reference: DYNR/netbird#8211