Add 7.0-preview5 SHA hash algorithm known issue

[eerhardt]

No description provided.

[vcsjones]

Technical details look right to me.

[bartonjs]

It can't happen for single-page requests... do we know the upper-bound on "safe" values?

Assume all bytes are valued greater than 99. So it's something like {"digest":"SHA256","content":[]} with the middle filled in with Max(0, (4 * content.Length) - 1) on a 1024-byte page. If my identifiers and whitespace is right, then that's 32 overhead bytes, so 4L - 1 < (1024-32) => 4L - 1 < 992, 4L < 993, L < 248.25, so the hash of anything 248 bytes or smaller is immune to the race.

Is that worth mentioning (after verifying the numbers)?

[eerhardt]

I'm not sure it is worth mentioning. Could someone do something useful with that information?

If someone is affected by this - I would tell them to stay on 7.0-preview4 until 7.0-preview6 was released. That seems like the most appropriate action rather than trying to workaround it just for preview5.