Description:
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This one seems to be sourced back since quite some time (at least from 5.6.30 till 8.0.8). Right now I do not have the time for posting too many details but it should be pretty clear to understand by looking at streams/filter.c, function _php_stream_filter_flush, then the loop with current = filter and then referencing filter->fops->filter() instead of current->fops->filter().



Test script:
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class some_user_filter {
...
}
stream_filter_register("some.filter", "some_user_filter");
$f = fopen("test", "wb");
$flt1 = stream_filter_append($f, "zlib.deflate", STREAM_FILTER_WRITE);
$flt2 = stream_filter_append($f, "some.filter", STREAM_FILTER_WRITE);
fwrite($f, "test");
stream_filter_remove($flt1); // this line will fail and at the end of the script a segfault / or MS Don't send / access violation
fwrite($f, "test"1);