John Bailey

Microsoft | Service Ops 2 | Exchange | MSFT Corp & O365 Dedicated

O365: CDN Change Causes OWA Client Error

O365: CDN Change Causes OWA Client Error

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Recently, we've seen a pattern of escalations wherein users are no longer able to access OWA. Specifically, the error will be similar to the following:

In the details, we'll see the error we're concerned with:

X-OQA-Error: ClientError;exMsg=’_g’ is undefined; file=

If we use Network Tracing (F12 in Internet Explorer) [or Fiddler] we'll see a failure to connect to the CDN:

The connection to '' failed. <br />Error: ConnectionRefused (0x274d). <br />System.Net.Sockets.SocketException No connection could be made because the target machine actively refused it

Using ARIN, we can check to make sure that the CDN (Content Delivery Network) we're trying to hit is owned by Akamai.

The return we're receiving, highlighted, is because the client cannot load 'boot.worldwide.0.mouse.js' from the CDN. This is evidenced by the refusal to connect to the RES server, highlighted.

The root cause of this issue is the configuration of the customer-owned firewall. This is evidenced by the client's inability to connect to specific CDN and other users are able to use OWA sans issue; notably, because they are connecting to another CDN ('', for example).

Since the CDN is controlled by a third-party and we have no way to predict which hosts will be up/in use/referred, our recommendation is to use URL-based filtering. You can read the EHLO blog post (written by our very own Tim Heeney) on the recommendation for URL-based filtering, here:

  • I think there is a java script email trojan horse being setup and it runs (boot.worldwide.3.mouse.js) and others to cause a error for further injection exploit. Does anyone know code well enough to look through an email I just got today, the source has the reference text and more. I also got a social engineering call shortly before the email, trying to convince me to open the email immediately to confirm attendance for an event.

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