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BBR is a new congestion control algorithm proposed by Google that builds a model of the network path consisting of its bottleneck bandwidth and RTT to govern its sending rate rather than packet loss (like CUBIC and many other popular congestion control algorithms). Loss-based congestion control has been shown to be vulnerable to acknowledgment manipulation attacks. However, no prior work has investigated how to design such attacks for BBR, nor how effective they are in practice. In this paper we systematically analyze the vulnerability of BBR to acknowledgement manipulation attacks. We create the first detailed BBR finite state machine and a novel algorithm for inferring its current BBR state at runtime by passively observing network traffic.We then adapt and apply a TCP fuzzer to the Linux TCP BBR v1.0 implementation. Our approach generated 30,297 attack strategies, of which 8,859 misled BBR about actual network conditions. From these, we identify 5 classes of attacks causing BBR to send faster, slower or stall. We also found that BBR is immune to acknowledgment burst, division and duplication attacks that were previously shown to be effective against loss-based congestion control such as TCP New Reno.
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This content will become publicly available on July 8, 2026
Internet Connection Splitting: What’s Old is New Again
In the 1990s, many networks deployed performance-enhancing proxies (PEPs) that transparently split TCP connections to aid performance, especially over lossy, long-delay paths. Two recent developments have cast doubts on their relevance: the BBR congestion-control algorithm, which de-emphasizes loss as a congestion signal, and the QUIC transport protocol, which prevents transparent connection-splitting yet empirically matches or exceeds TCP’s performance in wide deployment, using the same congestion control. In light of this, are PEPs obsolete? This paper presents a range of emulation measurements indicating: “probably not.” While BBR’s original 2016 version didn’t benefit markedly from connection-splitting, more recent versions of BBR do and, in some cases, even more so than earlier “loss-based” congestion-control algorithms. We also find that QUIC implementations of the “same” congestion-control algorithms vary dramatically and further differ from those of Linux TCP—frustrating head-to-head comparisons. Notwithstanding their controversial nature, our results suggest that PEPs remain relevant to Internet performance for the foreseeable future.
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- PAR ID:
- 10617781
- Editor(s):
- Altınbüken, Deniz; Stutsman, Ryan
- Publisher / Repository:
- USENIX Association
- Date Published:
- ISBN:
- 978-1-939133-48-9
- Page Range / eLocation ID:
- 867-887
- Format(s):
- Medium: X Other: pdf
- Location:
- Boston, MA
- Sponsoring Org:
- National Science Foundation
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