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Bug #72053 Multipart request is parsed differently for nearly equal "Content-Disposition"
Submitted: 2016-04-18 21:17 UTC Modified: 2021-03-10 13:05 UTC
Avg. Score:3.0 ± 0.0
Reproduced:1 of 1 (100.0%)
Same Version:0 (0.0%)
Same OS:0 (0.0%)
From: mail at michael-kaufmann dot ch Assigned:
Status: Verified Package: *General Issues
PHP Version: 7.4 OS: Linux
Private report: No CVE-ID: None
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 [2016-04-18 21:17 UTC] mail at michael-kaufmann dot ch
Fuzz testing revealed that this multipart request is parsed differently, depending on the number of 'a' characters:

Content-Disposition: form-data; name="test"; aaaaaaaaa...aaaaaaaaaa:; filename="test.txt"

This is a test

For up to 5074 'a' characters, PHP parses this as a file upload: _FILES["test"] contains an array.

For 5075 'a' characters and more, PHP parses this as a POST parameter: _POST["test"] contains the string "This is a test".

This is very strange behavior. I expect that PHP parses these requests the same way, regardless of the number of 'a' characters.

Test script:
	printf -- "--BOUNDARY\r\n"
	printf -- "Content-Disposition: form-data; name=\"test\"; "
	printf -- "a%.0s" {1..5074}
	printf -- ":; filename=\"test.txt\"\r\n"
	printf -- "\r\n"
	printf -- "This is a test\r\n"
	printf -- "--BOUNDARY--"
) > /tmp/test.dat

curl -H "Content-Type: multipart/form-data; boundary=BOUNDARY" --data-binary @/tmp/test.dat http://.../phpinfo.php


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 [2016-06-12 18:19 UTC] mail at michael-kaufmann dot ch
-PHP Version: 5.6.20 +PHP Version: 7.0.7
 [2016-06-12 18:19 UTC] mail at michael-kaufmann dot ch
This is what happens:

next_line() in rfc1867.c returns a partial (truncated) header line for very long headers. multipart_buffer_headers() processes this partial header line like a complete header line if it contains a colon (":"). The remaining part of the header line is then processed as a separate header.

In the example, the "Content-Disposition" header is split like this:

First header:
- name: Content-Disposition
- value: form-data; name="test"; aaaaaaaaa...aaaaaaaaaa

Second header:
- name: (empty)
- value: ; filename="test.txt"
 [2021-03-10 13:05 UTC]
-Status: Open +Status: Verified -PHP Version: 7.0.7 +PHP Version: 7.4
 [2021-03-10 13:05 UTC]
Thanks, you're analysis looks right.  A possible solution might be
to add a flag to multipart_buffer which signals the partial line,
and to catch that like we already catch lines beginning with
whitespace (to support line folding)[1].

[1] <>
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