[wp-trac] [WordPress Trac] #34222: Impossible to correctly make a REGEXP meta query's value safe from untrusted input

[WordPress Trac]

#34222: Impossible to correctly make a REGEXP meta query's value safe from
untrusted input
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 Reporter:  johnbillion   |       Owner:
     Type:  defect (bug)  |      Status:  new
 Priority:  normal        |   Milestone:  Awaiting Review
Component:  Query         |     Version:
 Severity:  normal        |  Resolution:
 Keywords:  dev-feedback  |     Focuses:
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Comment (by boonebgorges):

 In my testing, I'm seeing the same SQL as you're reporting. But the SQL is
 correctly matching posts. As far as I can see, in `WHERE meta_value REGEXP
 '^\\$100'`, MySQL inteprets the first slash as escaping the second one as
 a literal slash, and it then interprets the literal slash as escaping the
 `$`, which inside of a `REGEXP` means that it's not parsed as a regex
 special character. See attached screenshot.

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Ticket URL: <https://core.trac.wordpress.org/ticket/34222#comment:1>
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