The Shœstring Foundation Weblog, Miscellaneous Byproducts
bauerm (at) shoestringfoundation · org
Vignettes by George Herriman and a small program
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Look in the dusty corners!
A prediction (which you can help to make self-fulfilling): we will find security holes in implementations of
protocol features which are
- hardly ever used
- not really understood
Enough for now …
- HTML &
- RFC 2397 defines
a URL type which carries its own content. This could play havoc with
HTML content filters, filtering proxies, and so-called "browser
security settings". Simply base64 the exploit and put it in
<a href="data:base64...">. You can also
put iframes in
data: URLs, which in turn …
After a list of devious attacks on TCP (e.g.
Congestion Control Attack, Timestamp problems and ICMP based attacks),
it seems as if even the basic protocols are not really well understood
(or implemented). What happens in each of the thousands of
TCP/IP stack implementations if they receive
- ICMP Redirect (perhaps as part of a DDoS attack)?
- ICMP EchoReq with a multicast source address (and they joined that
- IPv6 options
- I looked over the basic IPv6 RFCs (
recently. Very impressive, they defined a lot of really
incredible stuff. For example
While there are some compliance testing efforts, there seem
to be no checks about handling of non-compliant datagrams.
What happens if a datagram carries two routing headers,
three destination option headers, undefined NextHeader
values, or a Jumbogram header indicating a payload
of 4 Gigabyte on an ordinary ether interface?
- the IPv6 Destination Options Header (RFC2460, Section 4.6)
is an optional header that allows to pad datagrams with zeros.
- the IPv6 Routing Header (RFC2460, Section 4.6) defines
up to 127 hops through which a datagram should travel.
It specifies the hops by addresses, so that the header
alone can be up to 16 * 127 + 4 = 2036 bytes
long. The routing header may not be fragmented (RFC2460, Section 4.5),
and the minimum MTU is 1280 (RFC2460, Section 5). It makes the
- to compute the UDP body checksum, an IPv6 pseudo-header
has to be constructed in memory. The UDP checksum ignores the headers
between the address part and the UDP header, except when
there's a routing header present, in which case it has to
be parsed for the final hop, which will then be included
in the pseudo-header. Simple, fast, efficient.
- Diverse pranks with Unicode are making the round (e.g.
shoestringfoundation's very own UTFbiffier), and the various
hacks to get wide-char support in standard applications,
and then there's Internationalized Domain Names
and useful character encodings in X509 (for example Teletext
and T61Sting which includes really suprising chars,
see Peter Gutmann's highly readable X.509 style guide).
All that calls for further interesting exploits on the user interface.
- ANSI terminal viruses (ok, it's viri, but tell that
to the walri)
- We terribly ε¦ïʈè
tend to use command line interfaces on terminals, consoles,
xterms or even screen.
But there's been lots of interesting attacks involving
magic escape sequences.
recent paper by H.D. Moore points out that this is a pending
- URG flags and pointers
- The TCP urgent feature implements the strange ITU-y idea
of sideband signaling. It basically tells the socket
that there's much more interesting data somewhere
later in the TCP stream. Practically no program uses this,
but who knows what shenanigans might be caused by an
URG pointer in a Jumboframe …