I have used the rule

#disable Post scanning for upload files
SetEnvIfNoCase Content-Type "^multipart/form-data" "MODSEC_NOPOSTBUFFERING=Do not buffer file uploads"

When multipart/form-data is received, apache thread terminated with following in error_log

[Tue Oct 12 14:14:26 2004] [notice] child pid 24935 exit signal Segmentation fault (11)

I have set debug level to 4, and the log contains:

[12/Oct/2004:14:14:25 +0800] [_default_/sid#809f020][rid#82b54a0][/ittest/modules/newbb/post.php] sec_check_access, path=(null)
[12/Oct/2004:14:14:25 +0800] [_default_/sid#809f020][rid#82b54a0][/ittest/modules/newbb/post.php] Normalised REQUEST_URI: "/ittest/modules/newbb/post.php"
[12/Oct/2004:14:14:25 +0800] [_default_/sid#809f020][rid#82b54a0][/ittest/modules/newbb/post.php] Parsing arguments...
[12/Oct/2004:14:14:25 +0800] [_default_/sid#809f020][rid#82b54a0][/ittest/modules/newbb/post.php] Adding cookie "lx006app_kmbh_com_hk_9080_ittest_newbb_10_LastVisit"="1097561646"
[12/Oct/2004:14:14:25 +0800] [_default_/sid#809f020][rid#82b54a0][/ittest/modules/newbb/post.php] Adding cookie "lx006app_kmbh_com_hk_9080_ittest_newbb_10_LastVisitTemp"="1097561621"
[12/Oct/2004:14:14:25 +0800] [_default_/sid#809f020][rid#82b54a0][/ittest/modules/newbb/post.php] Adding cookie "lx006app_kmbh_com_hk_9080_ittest_newbb_10_forum_lastview"="a:1:{i:1;i:1097561638;}"
[12/Oct/2004:14:14:25 +0800] [_default_/sid#809f020][rid#82b54a0][/ittest/modules/newbb/post.php] Adding cookie "PHPSESSID"="9f1b8e18d45bc5ec6393dca955406bb4"
[12/Oct/2004:14:14:25 +0800] [_default_/sid#809f020][rid#82b54a0][/ittest/modules/newbb/post.php] content-type = "multipart/form-data; boundary=----------------
[12/Oct/2004:14:14:25 +0800] [_default_/sid#809f020][rid#82b54a0][/ittest/modules/newbb/post.php] read_post_payload: POST scanning turned off dynamically (MODSEC_NOPOSTBUFFERING=Do not buffer file uploads)

-- EOF --

After changing the rule to :
SecFilterSelective HTTP_Content-Type "^multipart/form-data" "allow"

The transaction can be completed sucessfully.

Also, following rule in the documentation seems to be incorrect :

    # Only accept request encodings we know how to handle
    # we exclude GET requests from this because some (automated)
    # clients supply "text/html" as Content-Type
    SecFilterSelective REQUEST_METHOD "!^GET$" chain
    SecFilterSelective HTTP_Content-Type "!^(|application/x-www-form-urlencoded|multipart/form-data)$"

since multipart/form-data include ";boundary ...." in Content-Type.

Version : mod_security 1.8.4
Apache : 2.0.40 (bundled in RedHat 8.0)

Thanks & Regards,

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