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=> [3] no error means the first byte of `hostname` is in hexdigits
$ php check-first-char-is-hex.php /etc/hostname && echo ok
ok
+-------------------------------------------------------------------------+
Once the general idea took shape, the next step was building a complete
character-mapping table and iterating through the entire file byte by
byte. This process involved even more sophisticated filter tricks - such
as swapping byte order with different endianness, or fine-tuning encoding
combinations to get more precise results. Honestly, just looking at
@hashkitten's code gives me a headache; I can't imagine how much time he
spent grinding through this!
And once that barrier fell, the entire community jumped right in, pushing
this attack even further. First, @remsio released his own tool [67]. Then
@cfreal stepped up, not only adding custom suffixes [68], but also
sprinkling some serious magic [69] to perfect the attack. With all these
efforts combined, I think we can finally say we've conquered "Blind AFR"
once and for all in PHP!
============================================
| Level Max - Filter Chain ~After Story~ |
============================================
Aside from conquering LFI and Blind AFR, filter chains had a few more fun
twists. While experimenting with encoding combinations, @cfreal somehow
discovered a new memory corruption bug in the GNU C Library. He later
published a fantastic series of articles [70], detailing how to achieve
RCE with just a limited out-of-bounds write. And all these developments
eventually led the PHP community to consider "limiting the number of
Filter Chains" [71], effectively bringing the entire issue to a close.
Looking back at this twenty-year evolution of LFI - from the early days
when the Infosec community was all about finding better ways to control
file contents, to CTF players exploring generic methods to leave temporary
files behind, and finally to @loknop and @hashkitten shifting everyone's
attention back to PHP filters - this must be a truly epic journey, shaped
by the CTF, PHP, and Infosec communities all together!
------[ 4.2 - PHAR Deserialization
As more and more people realized how dangerous deserialization could be,
developers became super cautious with `unserialize()`, causing such issues
to gradually fade away. But what if today, we could break the assumption
that "only `unserialize()` can trigger an attack." Could we make
deserialization great again?
Well, I think "PHAR Deserialization" coming up next is probably the best
showcase - it can turn practically any *file operation* straight back into
a deserialization attack! And I think I can proudly say that I was the
first person to bring this technique to the world (correct me if I'm
wrong). This technique originally appeared in my challenge at HITCON CTF
2017 [72]. However, it seems this trick stayed mostly within the CTF
community [73] and didn't really gain broader attention.
Of course, I know Sam Thomas also presented this attack surface [74] at
Black Hat USA 2018 (I was literally sitting in the audience right there!).
You wouldn't believe how shocked I was! We chatted a bit afterward and
realized we'd both independently discovered the same idea. Honestly, that
made me respect Thomas even more, because while I'd just used this trick
for fun in CTFs, he took it much further by exploring its real-world
impacts and successfully exploiting it in well-known projects like Typo3,
WordPress, and even TCPDF. It was Thomas who really put this trick on the
map, so please give him a big round of applause, too!
But anyway - please allow me to include "PHAR Deserialization" in this
section, and share the story!
=> I'd almost forgotten about this IRC log [75] XD
---------------------------------------------------------------------------
[13:14] <Beched> omg is this common knowledge? =)
[13:14] <Beched> where did you learn that PHP deserializes metadata in phars?
[13:14] <Beched> somehow no one knew that among us
[13:27] <orange_> I read the PHP source code in my free time
[13:27] <orange_> I think both tricks are not seen on the Internet
[13:27] <orange_> That's why nobody solve it ! :(
[13:38] <Beched> yeah that's cool
[13:38] <Beched> turning arbitrary read into unserialize
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=============================
| Level 0 - What is PHAR? |
=============================
Just like JAR files in Java, "PHAR" is a PHP-specific archiving format
designed for easier deployment. While designing this format, PHP also
included a dedicated field to store the file's own metadata. And to make
sure deployed applications could easily access this information later on,