Corrupted image_captcha In Drupal
2016-04-23
I have noticed that the image_captcha Drupal module has been showing empty images on some of the websites I administer. When checking the cause of this I tried to view the image directly and got:
What baffled me was the fact there were errors in either Drupal’s or the server’s error logs.
So I downloaded the file through curl
# Save the corrupted image to disk
curl 'http://site/en/image_captcha?sid=2481564&ts=1461450252' -o /root/img.jpg
After checking the binary content of the file I noticed the following
# get the binary content of the file
hexdump -x img.jpg | head
Valid JPG file (Some spaces removed to improve appearance)
0000000 d8ff e0ff 1000 464a 4649 0100 0001 0100
0000010 0100 0000 feff 3e00 5243 4145 4f54 3a52
0000020 6720 2d64 706a 6765 7620 2e31 2030 7528
0000030 6973 676e 4920 474a 4a20 4550 2047 3876
0000040 2930 202c 6564 6166 6c75 2074 7571 6c61
0000050 7469 0a79 dbff 4300 0800 0606 0607 0805
0000060 0707 0907 0809 0c0a 0d14 0b0c 0c0b 1219
0000070 0f13 1d14 1f1a 1d1e 1c1a 201c 2e24 2027
0000080 2c22 1c23 281c 2937 302c 3431 3434 271f
0000090 3d39 3238 2e3c 3433 ff32 00db 0143 0909
Invalid JPG file (Some spaces removed to improve appearance)
0000000 ff0a ffd8 00e0 4a10 4946 0046 0101 0000
0000010 0001 0001 ff00 00fe 433e 4552 5441 524f
0000020 203a 6467 6a2d 6570 2067 3176 302e 2820
0000030 7375 6e69 2067 4a49 2047 504a 4745 7620
0000040 3038 2c29 6420 6665 7561 746c 7120 6175
0000050 696c 7974 ff0a 00db 0043 0608 0706 0506
0000060 0708 0707 0909 0a08 140c 0c0d 0b0b 190c
0000070 1312 140f 1a1d 1e1f 1a1d 1c1c 2420 272e
0000080 2220 232c 1c1c 3728 2c29 3130 3434 1f34
0000090 3927 383d 3c32 332e 3234 dbff 4300 0901
If you notice the invalid file has an extra ff0a at the beginning. This means there is an extra blank line before the <?php tag in one of the files. After digging around it was index.php for me, could be settings.php or an incorrectly edited module file.
Also, it could be a PHP file saved with UTF-8 or some other encoding.
The reason this doesn’t generate any errors if the fact that:
empty-line
<?php
Is valid PHP syntax that generates an empty line and then the output of whatever PHP come that comes after.
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