In PHP prior to 8.1.32, 8.2.28, 8.3.19, and 8.4.5, the header parser of the http stream parser does not understand that a header line beginning with whitespace continues the previous header and instead considers every newline to be a header separator. Users of the http stream wrapper might interpret the response with an incorrect MIME type and more generally might misparse the response, for example by incorrectly determining which response headers belong to the final response if a redirect happened.