Lone packet cripples telco networks

Telecommunications infrastructure is riddled with security holes so severe that a handful of malformed packets could take down GSM communications systems, according to veteran pen tester and founder of Qualys, Philippe Langlois.

He said the security flaws persisted due to inaction by telco equipment manufacturers, the complexity of networks, and a lack of security oversight.

In January 2010, Langlois, now director of P1 Security, discovered that a single malformed packet could disable one of the Home Location Register server clusters which store GSM subscriber details as part of the global SS7 network.

This packet could be sent from within any network or even femtocells, he said.

"We were able to remotely crash HLR frontend for two minutes each by sending one malformed packet," Langlois told SC.

"That means with 20 packets a minute, you would crash the world's HLR. This means there is no communication possible for that operator in a country."

He said 83 per cent of telco operators do not apply traffic filtering over the SS7 network.

In further research to be released within weeks, Langlois will detail how similar attacks could cripple GRPS systems. The world-wide SS7 report was a product of Langlois' 15 years of telecommunications research.

Tech sandwiches

The SS7 attacks were but one example of how large holes in telecommunications infrastructure could be exploited.

Telcos the world over were running networks tantamount to "technology sandwiches" where layers of legacy kit had created such high complexity that operators were unaware of glaring holes which Langlois regularly revealed in penetration tests.

Other operators were less fortunate, and had such flaws exploited by malicious actors.

Recently in Eastern Europe, a telco had routed half of its telecommunications traffic through its rival's network, forcing the company to fund a significant bandwidth burden. It had not yet settled the case.

Such attacks were most common within Eastern Europe but the region was also home to the most security-savvy telcos who had the best understanding of their network exposures,  according to Langlois.

He said most  vulnerabilities existed because equipment providers suppressed knowledge of them to avoid what could amount to hundreds of millions of dollars in cash from network outages.

"It is troubling to see very talented, expert people [at telcos] who are shielded from the reality of their network by the vendor who has no interest in educating them about the telecom security and exposure of their own networks."

"It feels like the 1980s in terms of security."

Langlois said he often accessed telco networks using services that administrators were unaware were active.  

"We accessed [an operator's] systems through their x25 network which they never knew was running because the network vendor never disclosed it -- it was just underlying technology."

"All of these change management, configuration management and monitoring systems are specific to one kind of equipment, and you need to access several of these to get a clear vision of what is on your systems."

Langlois and MegaPay director Emmanuel Gadaix spoke at Hack In The Box Malyasia. His presentation slides are available (pdf).

Copyright © SC Magazine, Australia