Two security researchers have demonstrated a new technique to stealthily
intercept internet traffic on a scale previously presumed to be
unavailable to anyone outside of intelligence agencies like the National
Security Agency.
The tactic exploits the internet routing protocol BGP (Border Gateway
Protocol) to let an attacker surreptitiously monitor unencrypted
internet traffic anywhere in the world, and even modify it before it
reaches its destination.
The demonstration is only the latest attack to highlight fundamental
security weaknesses in some of the internet’s core protocols. Those
protocols were largely developed in the 1970s with the assumption that
every node on the then-nascent network would be trustworthy. The world
was reminded of the quaintness of that assumption in July, when
researcher
Dan Kaminsky disclosed a serious vulnerability in the DNS system. Experts say the new demonstration targets a potentially larger weakness.
"It’s a huge issue. It’s at least as big an issue as the DNS issue,
if not bigger," said Peiter "Mudge" Zatko, noted computer security
expert and former member of the L0pht hacking group, who testified to
Congress in 1998 that he could bring down the internet in 30 minutes
using a similar BGP attack, and disclosed privately to government agents
how BGP could also be exploited to eavesdrop. "I went around screaming
my head about this about ten or twelve years ago…. We described this to
intelligence agencies and to the National Security Council, in detail."
The man-in-the-middle attack exploits BGP to fool routers into re-directing data to an eavesdropper’s network.
Anyone with a BGP router (ISPs, large corporations or
anyone with space at a carrier hotel) could intercept data headed to a target IP address or group of addresses. The attack intercepts only traffic headed
to
target addresses, not from them, and it can’t always vacuum in traffic
within a network — say, from one AT&T customer to another.
The method conceivably could be used for corporate espionage,
nation-state spying or even by intelligence agencies looking to mine
internet data without needing the cooperation of ISPs.
BGP eavesdropping has long been a theoretical weakness, but no one is
known to have publicly demonstrated it until Anton "Tony" Kapela, data
center and network director at
5Nines Data, and Alex Pilosov, CEO of
Pilosoft,
showed their technique at the recent DefCon hacker conference. The pair
successfully intercepted traffic bound for the conference network and
redirected it to a system they controlled in New York before routing it
back to DefCon in Las Vegas.
The technique, devised by Pilosov, doesn’t exploit a bug or flaw in BGP. It simply exploits the natural way BGP works.
"We’re not doing anything out of the ordinary," Kapela told
Wired.com. "There’s no vulnerabilities, no protocol errors, there are no
software problems. The problem arises (from) the level of
interconnectivity that’s needed to maintain this mess, to keep it all
working."
The issue exists because BGP’s architecture is based on trust. To
make it easy, say, for e-mail from Sprint customers in California to
reach Telefonica customers in Spain, networks for these companies and
others communicate through BGP routers to indicate when they’re the
quickest, most efficient route for the data to reach its destination.
But BGP assumes that when a router says it’s the best path, it’s telling
the truth. That gullibility makes it easy for eavesdroppers to fool
routers into sending them traffic.
Here’s how it works. When a user types a website name into his
browser or clicks "send" to launch an e-mail, a Domain Name System
server produces an IP address for the destination. A router belonging to
the user’s ISP then consults a BGP table for the best route. That table
is built from announcements, or "advertisements," issued by ISPs and
other networks — also known as Autonomous Systems, or ASes — declaring
the range of IP addresses, or IP prefixes, to which they’ll deliver
traffic.
The routing table searches for the destination IP address among those
prefixes. If two ASes deliver to the address, the one with the more
specific prefix "wins" the traffic. For example, one AS may advertise
that it delivers to a group of 90,000 IP addresses, while another
delivers to a subset of 24,000 of those addresses. If the destination IP
address falls within both announcements, BGP will send data to the
narrower, more specific one.
To intercept data, an eavesdropper would advertise a range of IP
addresses he wished to target that was narrower than the chunk
advertised by other networks. The advertisement would take just minutes
to propagate worldwide, before data headed to those addresses would
begin arriving to his network.
The attack is called an IP hijack and, on its face, isn’t new.
But in the past, known IP hijacks have created outages, which,
because they were so obvious, were quickly noticed and fixed. That’s
what occurred earlier this year when
Pakistan Telecom inadvertently hijacked YouTube traffic from around the world. The traffic hit a
dead-end in Pakistan, so it was apparent to everyone trying to visit YouTube that something was amiss.
Pilosov’s innovation is to forward the intercepted data silently to the actual destination, so that no outage occurs.
Ordinarily, this shouldn’t work — the data would boomerang back to
the eavesdropper. But Pilosov and Kapela use a method called AS path
prepending that causes a select number of BGP routers to reject their
deceptive advertisement. They then use these ASes to forward the stolen
data to its rightful recipients.
"Everyone … has assumed until now that you have to break something
for a hijack to be useful," Kapela said. "But what we showed here is
that you don’t have to break anything. And if nothing breaks, who
notices?"
Stephen Kent, chief scientist for information security at BBN
Technologies, who has been working on solutions to fix the issue, said
he demonstrated a similar BGP interception privately for the Departments
of Defense and Homeland Security a few years ago.
Kapela said network engineers might notice an interception if they
knew how to read BGP routing tables, but it would take expertise to
interpret the data.
A handful of
academic groups collect
BGP routing information
from cooperating ASes to monitor BGP updates that change traffic’s
path. But without context, it can be difficult to distinguish a
legitimate change from a malicious hijacking. There are reasons traffic
that ordinarily travels one path could suddenly switch to another — say,
if companies with separate ASes merged, or if a natural disaster put
one network out of commission and another AS adopted its traffic. On
good days, routing paths can remain fairly static. But "when the
internet has a bad hair day," Kent said, "the rate of (BGP path) updates
goes up by a factor of 200 to 400."
Kapela said eavesdropping could be thwarted if ISPs aggressively
filtered to allow only authorized peers to draw traffic from their
routers, and only for specific IP prefixes. But filtering is labor
intensive, and if just one ISP declines to participate, it "breaks it
for the rest of us," he said.
"Providers can prevent our attack absolutely 100 percent," Kapela
said. "They simply don’t because it takes work, and to do sufficient
filtering to prevent these kinds of attacks on a global scale is cost
prohibitive."
Filtering also requires ISPs to disclose the address space for all
their customers, which is not information they want to hand competitors.
Filtering isn’t the only solution, though. Kent and others are
devising processes to authenticate ownership of IP blocks, and validate
the advertisements that ASes send to routers so they don’t just send
traffic to whoever requests it.
Under the scheme, the five regional internet address registries would
issue signed certificates to ISPs attesting to their address space and
AS numbers. The ASes would then sign an authorization to initiate routes
for their address space, which would be stored with the certificates in
a repository accessible to all ISPs. If an AS advertised a new route
for an IP prefix, it would be easy to verify if it had the right to do
so.
The solution would authenticate only the first hop in a route to
prevent unintentional hijacks, like Pakistan Telecom’s, but wouldn’t
stop an eavesdropper from hijacking the second or third hop.
For this, Kent and BBN colleagues developed Secure BGP (SBGP), which
would require BGP routers to digitally sign with a private key any
prefix advertisement they propagated. An ISP would give peer routers
certificates authorizing them to route its traffic; each peer on a route
would sign a route advertisement and forward it to the next authorized
hop.
"That means that nobody could put themselves into the chain, into the
path, unless they had been authorized to do so by the preceding AS
router in the path," Kent said.
The drawback to this solution is that current routers lack the memory
and processing power to generate and validate signatures. And router
vendors have resisted upgrading them because their clients, ISPs,
haven’t demanded it, due to the cost and man hours involved in swapping
out routers.
Douglas Maughan, cybersecurity research program manager for the DHS’s
Science and Technology Directorate, has helped fund research at BBN and
elsewhere to resolve the BGP issue. But he’s had little luck convincing
ISPs and router vendors to take steps to secure BGP.
"We haven’t seen the attacks, and so a lot of times people don’t
start working on things and trying to fix them until they get attacked,"
Maughan said. "(But) the YouTube (case) is the perfect example of an
attack where somebody could have done much worse than what they did."
ISPs, he said, have been holding their breath, "hoping that people don’t discover (this) and exploit it."
"The only thing that can force them (to fix BGP) is if their customers … start to demand security solutions," Maughan said.
—
(Image: Alex Pilosov (left) and Anton "Tony" Kapela demonstrate their
technique for eavesdropping on internet traffic during the DefCon
hacker conference in Las Vegas earlier this month.
(Wired.com/Dave Bullock)
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