Microsoft Exchange year 2022 bug in FIP-FS breaks email delivery

Microsoft Exchange server bug

Microsoft Exchange on-premise servers cannot deliver email starting on January 1st, 2022, due to a "Year 2022" bug in the FIP-FS anti-malware scanning engine.

Starting with Exchange Server 2013, Microsoft enabled the FIP-FS anti-spam and anti-malware scanning engine by default to protect users from malicious email.

Microsoft Exchange Y2K22 bug

According to numerous reports from Microsoft Exchange admins worldwide, a bug in the FIP-FS engine is blocking email delivery with on-premise servers starting at midnight on January 1st, 2022.

Security researcher and Exchange admin Joseph Roosen said that this is caused by Microsoft using a signed int32 variable to store the value of a date, which has a maximum value of 2,147,483,647.

However, dates in 2022 have a minimum value of 2,201,010,001, which is greater than the maximum value that can be stored in the signed int32 variable, causing the scanning engine to fail and not release mail for delivery.

According to additional research on this issue, this is happening because Microsoft is using a signed int32 for the date and the new date value of 2,201,010,001 is over the max value of "long" int32 being 2,147,483,647. @MSFTExchange - Not sure why it was structured this way??
— Joseph Roosen (@JRoosen) January 1, 2022

When this bug is triggered, an 1106 error will appear in the Exchange Server's Event Log stating, "The FIP-FS Scan Process failed initialization. Error: 0x8004005. Error Details: Unspecified Error" or "Error Code: 0x80004005. Error Description: Can't convert "2201010001" to long."

Dear @msexchangeteam. The FIP-FS “Microsoft” Scan Engine Failed to Load. Can’t Convert “2201010001” to long.
— long wtf = 2201010001; (@miketheitguy) January 1, 2022

Microsoft will need to release an Exchange Server update that uses a larger variable to hold the date to officially fix this bug.

However, for on-premise Exchange Servers currently affected, admins have found that you can disable the FIP-FS scanning engine to allow email to start delivering again.

To disable the FIP-FS scanning engine, you can execute the following PowerShell commands on the Exchange Server:

Set-MalwareFilteringServer -Identity  -BypassFiltering $true
Restart-Service MSExchangeTransport

After the MSExchangeTransport service is restarted, mail will start being delivered again.

Unfortunately, with this unofficial fix, delivered mail will no longer be scanned by Microsoft's scanning engine, leading to more malicious emails and spam getting through to users.

Microsoft has confirmed that they are working on a fix and hope to have more information available later today.

We are aware of and working on an issue causing messages to be stuck in transport queues on Exchange Server 2016 and Exchange Server 2019. The problem relates to a date check failure with the change of the new year and it not a failure of the AV engine itself. This is not an issue with malware scanning or the malware engine, and it is not a security-related issue. The version checking performed against the signature file is causing the malware engine to crash, resulting in messages being stuck in transport queues.

We are actively working on resolving this issue and expect to release details on how to resolve this issue later today. In the meantime, if your organization performs malware scanning of messages outside of your on-premises Exchange servers (for example, by routing mail through Exchange Online, or by using a third-party message hygiene solution), you can bypass or disable malware scanning on your Exchange servers and clear your transport queues. You should use one of these workarounds only if you have an existing malware scanner for email other than the engine in Exchange Server.

BleepingComputer has also contacted Microsoft about the problem but has not received a response yet.

Update 1/1/22: Added information from Microsoft.

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Microsoft Exchange '2022' FIP-FS bug causes emails to get stuck

Microsoft Exchange year 2022 bug in FIP-FS breaks email delivery