That's not the same as finding a bytestring which hashes to a given SHA1, which is still easier than to find a bytestring with, together with a given ASCII pre- and postamble, will match that given SHA1.
I don't think there's a feasible attack for the latter. But as SHA1 is considered "broken enough" that it should be phased out, AFAIK current efforts on one-way hashes are more focused on trying to break the several candidates for SHA's replacement, than to break SHA1 'even more'.
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