I've found, by complete accident a very strange curl segfault produced by the following code:

    $ch = curl_init ("ftp://localhost/itworked.txt");
    curl_setopt($ch, CURLOPT_USERPWD, "php:foobar");
    $fr = fopen("curl_ex6.php");
    curl_setopt($ch, CURLOPT_INFILE, $fr);
    curl_setopt($ch, CURLOPT_UPLOAD, true);
    curl_exec($ch);
    fclose($fr);
    curl_close($ch);

Two important parts to this segfault:

   1) fopen() cannot actually be correctly formatted. It must fail to specify the mode. 

   2) The username, password set by curl_setopt must actually be a real username/password that works. If you provide a fake password, everything is fine.. but if you actually used a real password you segfault.


here's the BT:

#0  0x40259a85 in _IO_fread (buf=0x821ca25, size=1, count=16384, fp=0x0)
    at iofread.c:42
#1  0x08069893 in curl_read (data=0x821ca25 "", size=1, nmemb=16384,
    ctx=0x8217aac) at /usr/local/src/php-4.3.1/ext/curl/curl.c:394
#2  0x400f0842 in fillbuffer (conn=0x82130b0, bytes=16384) at transfer.c:137
#3  0x400f1c7e in Curl_readwrite (conn=0x82130b0, done=0xbfffccff "")
    at transfer.c:948
#4  0x400f24d2 in Transfer (conn=0x82130b0) at transfer.c:1247
#5  0x400f2a4e in Curl_perform (data=0x82183a8) at transfer.c:1586
#6  0x400f2dfc in curl_easy_perform (curl=0x82183a8) at easy.c:247
#7  0x0806b03d in zif_curl_exec (ht=1, return_value=0x820e73c, this_ptr=0x0,
    return_value_used=0) at /usr/local/src/php-4.3.1/ext/curl/curl.c:994
#8  0x0814c928 in execute (op_array=0x8213024)
    at /usr/local/src/php-4.3.1/Zend/zend_execute.c:1596
#9  0x0813a538 in zend_execute_scripts (type=8, retval=0x0, file_count=3)
    at /usr/local/src/php-4.3.1/Zend/zend.c:864
#10 0x081143f5 in php_execute_script (primary_file=0xbffffa40)
    at /usr/local/src/php-4.3.1/main/main.c:1573
#11 0x08154e9c in main (argc=2, argv=0xbffffae4)
    at /usr/local/src/php-4.3.1/sapi/cli/php_cli.c:746
#12 0x40207306 in __libc_start_main (main=0x815451c <main>, argc=2,
    ubp_av=0xbffffae4, init=0x806461c <_init>, fini=0x815d280 <_fini>,
    rtld_fini=0x4000d2dc <_dl_fini>, stack_end=0xbffffadc)