🐛 [Bug] Submission (smtp) Authentication With Scram Tries Using Imap AUTHENTICATE Command Instead Of Smtp AUTH Command
Introduction
In this article, we will discuss a bug in the cypht 2.4.0 library, where it tries to authenticate with a submission/smtp server using the IMAP AUTHENTICATE command instead of the SMTP AUTH command. This bug is significant because it can lead to authentication failures and prevent users from sending emails.
The Bug
When setting up cypht 2.4.0 to test for interoperability with the mox submission server, we encountered a bug where cypht tries to log in to check the credentials. It picks SCRAM, which is good, but it tries to use the command AUTHENTICATE on SMTP, which does not exist in SMTP. This command does exist in IMAP, and we suspect that the SCRAM code is shared between IMAP and SMTP, but it doesn't take this difference into account.
Debugging the Issue
To debug this issue, we looked at the mox submission server logs and saw the following output:
> 220 komijn.test.xmox.nl ESMTP mox v0.0.15-0.20250308080341-0857e81a6ccc+dirty-go1.24.1\r\n
< EHLO 0f5831cd80bb\r\n
> 250-komijn.test.xmox.nl\r\n250-PIPELINING\r\n250-SIZE 104857600\r\n250-REQUIRETLS\r\n250-AUTH SCRAM-SHA-256-PLUS SCRAM-SHA-256 SCRAM-SHA-1-PLUS SCRAM-SHA-1 CRAM-MD5 PLAIN LOGIN\r\n250-FUTURERELEASE 5184000 2025-05-08T11:28:17Z\r\n250-ENHANCEDSTATUSCODES\r\n250-8BITMIME\r\n250-LIMITS RCPTMAX=1000\r\n250 SMTPUTF8\r\n
< AUTHENTICATE SCRAM-SHA-1\r\n\r\n
> 500 5.5.1 unknown command (T1ziWP-GGO7qrINl8MLFNw)\r\n
> 500 5.5.1 unknown command (T1ziWP-GGO7qrINl8MLFNw)\r\n
We then looked at the cypht code and found the issue in the hm-smtp.php file:
https://github.com/cypht-org/cypht/blob/1ead675272181d5b9e4cf5672fd30f3acc1b4c07/modules/smtp/hm-smtp.php#L345
And in the scram.php file:
https://github.com/cypht-org/cypht/blob/1ead675272181d5b9e4cf5672fd30f3acc1b4c07/lib/scram.php#L51
Choosing SCRAM Mechanisms
We also noticed that the SCRAM mechanisms are chosen in order from weakest to strongest. This is intentional, as seen in the hm-smtp.php file:
https://github.com/cypht-org/cypht/blob/1ead675272181d5b9e4cf5672fd30f3acc1b4c07/modules/smtp/hm-smtp.php#L122
And in the hm-imap.php file:
https://github.com/cypht-org/cypht/blob/1ead675272181d5b9e4cf5672fd30f3acc1b4c07/modules/imap/hm-imap.php#L263
Conclusion
In conclusion, the bug in cypht 2.4.0 is significant and can lead to authentication failures and prevent users from sending emails. We have identified the issue and provided the necessary information to debug and fix the problem.
Version & Environment
We were using cypht 2.4.0 from a docker container. We tried the daily docker image, but it didn't start up due to errors around database migrations. We quickly reverted to 2.4.0 and looked at the code, which still has the issue in the master branch.
Recommendations
We recommend that the cypht developers fix this bug and release a new version of the library. In the meantime, users can use the workaround of using the SMTP AUTH command instead of the IMAP AUTHENTICATE command.
Future Work
Introduction
In our previous article, we discussed a bug in the cypht 2.4.0 library, where it tries to authenticate with a submission/smtp server using the IMAP AUTHENTICATE command instead of the SMTP AUTH command. In this article, we will provide a Q&A section to help answer some of the common questions related to this issue.
Q: What is the cause of this bug?
A: The cause of this bug is that the cypht library is using the IMAP AUTHENTICATE command instead of the SMTP AUTH command to authenticate with the submission/smtp server. This is likely due to a misunderstanding of the differences between IMAP and SMTP authentication.
Q: What are the consequences of this bug?
A: The consequences of this bug are that it can lead to authentication failures and prevent users from sending emails. This can be frustrating for users and can also lead to lost productivity and revenue.
Q: How can I fix this bug?
A: To fix this bug, you can use the workaround of using the SMTP AUTH command instead of the IMAP AUTHENTICATE command. Alternatively, you can wait for the cypht developers to fix this bug and release a new version of the library.
Q: Why is the SCRAM mechanism chosen in order from weakest to strongest?
A: The SCRAM mechanism is chosen in order from weakest to strongest because it is a security best practice to prioritize the strongest authentication mechanisms first. This helps to ensure that the most secure authentication method is used whenever possible.
Q: What is the difference between IMAP and SMTP authentication?
A: IMAP (Internet Message Access Protocol) and SMTP (Simple Mail Transfer Protocol) are two different protocols used for email communication. IMAP is used for retrieving and managing email messages, while SMTP is used for sending email messages. IMAP authentication is typically used for accessing email accounts, while SMTP authentication is used for sending email messages.
Q: Can I use the cypht library with other email providers?
A: Yes, you can use the cypht library with other email providers. However, you may need to modify the library to accommodate the specific authentication requirements of the email provider.
Q: How can I report bugs or issues with the cypht library?
A: You can report bugs or issues with the cypht library by submitting an issue on the cypht GitHub page. This will help the developers to identify and fix the issue as quickly as possible.
Q: What is the current status of the cypht library?
A: The cypht library is currently in version 2.4.0, and the bug we discussed in this article is still present in the master branch. However, the developers are working to fix this bug and release a new version of the library.
Q: Can I use the cypht library with other programming languages?
A: Yes, you can use the cypht library with other programming languages. However, you may need to modify the library to accommodate the specific requirements of the programming language.
Conclusion
In conclusion, the bug in the cypht 2.4.0 library is significant and can lead to authentication failures and prevent users from sending emails. We hope that this Q&A section has helped to answer some of the common questions related to this issue. If you have any further questions or concerns, please don't hesitate to contact us.