UDP targeted as DDoS-as-a-service boosts attack frequency by 58 per cent: Prolexic

Distributed denial of service (DDoS) attacks surged in in the last week of August and perpetrators favoured UDP-based attacks over previous-favourite HTTP and SYN attacks as use of DDoS-as-a-service offerings exploded during the third quarter, research from DDoS analysis firm Prolexic has shown.

Figures in the company's latest Quarterly Global DDoS Attack Report (registration required), compiled quarterly by the company's PLXsert security research arm, found that the overall number of DDoS attacks increased 58 per cent compared with the same period a year earlier. Most significant was the 265 per cent increase in 'reflection attacks', in which target servers are tricked into flooding a victim system with unwanted data chunks.

Attacks were 44 per cent shorter overall than in the previous quarter – lasting for an average of 21.33 hours versus 38 hours in Q2 – but 12.3 per cent longer than the 19-hour average a year earlier.

The figures suggested that the proportion of DDoS attacks utilising UDP fragments – in which a target system is bombarded with incomplete UDP packets that bog down victim systems in error-checking – jumped to 14.66 per cent during the quarter, compared with 8.7 per cent in the previous quarter.

By contrast, use of SYN floods – in which attackers flood a target system with unanswered TCP/IP synchronisation requests – dropped from 31.22 per cent of observed attacks in Q2 to just 18.16 per cent of attacks in the latest quarter. That put SYN attacks just a hair ahead of HTTP GET attacks, which were used in 18.0 per cent of DDoS incidents that Prolexic observed.

Prolexic attributed the rise in UDP-based DDoS attacks to global campaigns being waged using PHP booter Web shells that favoured the Layer 3 UDP attacks.

"Although PHP booter shells are capable of launching application layer attacks, the coding and customisation is slightly more complex than the average DDoS attack script, and therefore UDP floods were frequently chosen," the report notes, adding that "a significant portion" of the floods were reflected amplification attacks using DNS and CHARGEN servers to inundate targets with data traffic.

Such amplification attacks – whose increasing prevalence Prolexic attributed to a rise in the use of DDoS-as-a-service cloud offerings – work by tricking a target server into responding with a large volume of information, which is redirected at the target organisation when the attacker spoofs their IP address so it appears that the request came from the victim's computer.

For example, during the quarter WordPress blogs were targeted by an attack that used XML-RPC 'pingback' capabilities that prompted the site to respond with a large chunk of XML text. DNS servers are also frequently targeted as part of reflection attacks.

Infrastructure-layer attacks were by far the most common method of DDoS, accounting for 76.52 per cent of DDoS attacks during the quarter, with UDP, SYN, DNS and ICMP based attacks comprising the lion's share. Application-layer attacks, predominantly based on HTTP methods but also using SSL POST and SSL GET, were used in just 23.48% of attacks.

One significant change in the DDoS profile was the declining prevalence of the itsoknoproblembro (BroDoS) botnet, which Prolexic said "has been ineffective as a DDoS attack and propaganda tool due to Internet cleanup efforts and widespread knowledge about its attack methods and tools".

China retained its title as the primary source country for DDoS attacks, with 62.26 per cent of DDoS attacks coming from the country. Australia did not rank in the top 10 countries, which also included the US (9.06 per cent), South Korea (7.09 per cent), Brazil (4.46 per cent), and Russian Federation (4.45 per cent).

Interestingly, Indonesia – which bumped China out of first place as the origin of the most security attacks in Akamai Technologies' recent State of the Internet report – did not place in the Prolexic report, suggesting strong regional preferences for different types of attacks.

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