About

Hi everyone 👋 - I am Florian and I am a last year PhD student at the University of Vienna's Security & Privacy Research Group (SEC) and the Network & Critical Infrastructure Security Group (ERIS) at SBA-Research.

During my master studies I joined Team ERIS as a junior researcher. With my supervisor Johanna, we found an entry point for Internet-measurements in Austria (aim.sba-research.org). I am now pursuing a PhD in that field with the focus on measuring Internet standard adoption and compliance.

My research focuses on tracking protocol adoption and security, the transition to IPv6, and leveraging active measurements to detect Internet outages.

Measurement Platforms

To make my measurements accessible to everyone, I try to build open measurement platforms.

📧 Email Security

Ranks email servers.

📍 IP Endpoint

Tracks public IPs.

🌐🔌 Country Monitor

Detects Internet disruptions.

Talks

IMC ’25 🇺🇸

2025, Oct 28th, IMC
Tracking Internet Disruptions in Ukraine: Insights from Three Years of Active Full Block Scans
Madison, WI, USA.

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IMC ’25 — Madison, Wisconsin 🇺🇸

2025, Oct 28th
Tracking Internet Disruptions in Ukraine: Insights from Three Years of Active Full Block Scans

Event website: https://conferences.sigcomm.org/imc/2025/

ISMK ’25 🇩🇪

2025, Sept 17/18th, ISMK
From Ping to Blackout: Tracking Internet Disruptions in Ukraine Since 2022
Stralsund, DE.

IKT ’25 🇦🇹

2025, Jun 25/26th, IKT
Von Österreich zur Ukraine und zurück: Aktive Messungen zum Erkennen von Internetausfällen
Dornbirn, AT.

Meetup ’25 🇦🇹

2025, Feb 25th, Security Meetup
From Ping to Blackout: Active Measurements on Internet Disruptions in Ukraine Kherson
Dynatrace, Vienna, AT.

ATNOG ’25 🇦🇹

2025, Feb 24th, ATNOG 25/1
Von Österreich zur Ukraine und zurück: Aktive Messungen zum Erkennen von Internetausfällen
Linz AG, Linz, AT.

IKT ’24 🇦🇹

2024, Sept 18th, IKT
Analyse rerouting Internet in Kherson
Vienna, AT.

IMC ’24 🇪🇸

2024, Nov 05th, IMC
Destination Reachable: What ICMPv6 Error Messages Reveal About Their Sources
Madrid, ES.

ATC ’22 🇺🇸

2022, July, USENIX ATC
Not That Simple: Email Delivery in the 21st Century
Carlsbad, US.

Publications

Tracking Internet Disruptions in Ukraine: Insights from Three Years of Active Full Block Scans

Florian Holzbauer, Sebastian Strobl, Johanna Ullrich
Proceedings of the 2025 ACM Internet Measurement Conference (IMC '25), 280-294

Paper; SLIDES; DATA

BIBTEX

@inproceedings{holzbauer2025tracking,
author = {Holzbauer, Florian and Strobl, Sebastian and Ullrich, Johanna},
title = {Tracking Internet Disruptions in Ukraine: Insights from Three Years of Active Full Block Scans},
year = {2025},
isbn = {9798400718601},
publisher = {Association for Computing Machinery},
address = {New York, NY, USA},
url = {https://doi.org/10.1145/3730567.3764449},
doi = {10.1145/3730567.3764449},
abstract = {Numerous disruptions to Internet access have been reported during the war in Ukraine, including large-scale outages, damage to network infrastructure, surveillance, and censorship measures. However, most observations rely on local reports or monitoring systems within Ukraine. In this paper, we investigate whether the conflict's impact on Internet connectivity can be observed externally, from a vantage point outside Ukraine. Focusing on the Kherson region, which has remained on the frontline for over three years, we conduct an active measurement campaign probing the Ukrainian address space at two-hour intervals since March 2, 2022, the 7th day of the invasion, resulting in a country-wide dataset that spans the full duration of the conflict. Extending existing outage detection approaches, we infer three signals to detect Internet disruptions and refine the mapping of ASes and address blocks to specific regions. This allows us to assign disruptions to oblasts with greater confidence. Our results demonstrate that Internet disruptions caused by the war can be measured remotely by any host connected to the Internet. Our analysis provides new insights into the resilience of small regional providers and identifies periods when Ukraine's Internet infrastructure was under significant strain.},
booktitle = {Proceedings of the 2025 ACM Internet Measurement Conference},
pages = {474–492},
numpages = {19},
keywords = {outage detection, icmp, full block scans, ukraine, kherson},
location = {USA},
series = {IMC '25}
}

Destination Reachable: What ICMPv6 Error Messages Reveal About Their Sources

F Holzbauer, Markus Maier, Johanna Ullrich
Proceedings of the 2024 ACM Internet Measurement Conference (IMC '24), 280-294

PAPER; SLIDES; CODE

BIBTEX

@inproceedings{holzbauer2024reachable,
  title     = {Destination Reachable: What ICMPv6 Error Messages Reveal About Their Sources},
  author    = {Florian Holzbauer and Markus Maier and Johanna Ullrich},
  booktitle = {Proceedings of the 2024 ACM Internet Measurement Conference (IMC '24)},
  year      = {2024},
  location  = {Madrid, Spain},
  pages     = {1--15},
  publisher = {ACM},
  doi       = {10.1145/3646547.3688420},
}

Diffie-Hellman Picture Show: Key Exchange Stories from Commercial VoWiFi Deployments

GK Gegenhuber, F Holzbauer, PÉ Frenzel, E Weippl, A Dabrowski
33rd USENIX Security Symposium (USENIX Security '24), 451-468

PAPER; SLIDES; CODE ; MBN Parser

BIBTEX

@inproceedings{gegenhuber2024diffie,
  title={Diffie-Hellman Picture Show: Key Exchange Stories from Commercial VoWiFi Deployments},
  author={Gegenhuber, Gabriel K and Holzbauer, Florian and Frenzel, Philipp {\'E} and Weippl, Edgar and Dabrowski, Adrian},
  booktitle={33rd USENIX Security Symposium (USENIX Security 24)},
  year={2024}
}

Careless Whisper: Exploiting Stealthy End-to-End Leakage in Mobile Instant Messengers

GK Gegenhuber, M Günther, M Maier, A Judmayer, F Holzbauer, PÉ Frenzel, J Ullrich
arXiv preprint arXiv:2411.11194 (2024)

BIBTEX

@article{gegenhuber2024careless,
  title={Careless Whisper: Exploiting Stealthy End-to-End Leakage in Mobile Instant Messengers},
  author={Gegenhuber, Gabriel K and Guenther, Maximilian and Maier, Markus and Judmayer, Aljosha and Holzbauer, Florian and Frenzel, Philipp {\'E} and Ullrich, Johanna},
  journal={arXiv preprint arXiv:2411.11194},
  year={2024}
}

An Extended View on Measuring Tor AS-Level Adversaries

GK Gegenhuber, M Maier, F Holzbauer, W Mayer, G Merzdovnik
Computers & Security 132, 103302 (2023)

BIBTEX

@article{gegenhuber2023extended,
  title={An extended view on measuring tor as-level adversaries},
  author={Gegenhuber, Gabriel K and Maier, Markus and Holzbauer, Florian and Mayer, Wilfried and Merzdovnik, Georg and Weippl, Edgar and Ullrich, Johanna},
  journal={Computers \& Security},
  volume={132},
  pages={103302},
  year={2023},
  publisher={Elsevier}
}

Not That Simple: Email Delivery in the 21st Century

F Holzbauer, J Ullrich, M Lindorfer, T Fiebig
USENIX Annual Technical Conference (USENIX ATC '22), 295-308 (2022)

PAPER; SLIDES; APNIC-Blog; CODE

BIBTEX

@inproceedings {holzbauer2022email,
author = {Florian Holzbauer and Johanna Ullrich and Martina Lindorfer and Tobias Fiebig},
title = {Not that Simple: Email Delivery in the 21st Century},
booktitle = {2022 USENIX Annual Technical Conference (USENIX ATC 22)},
year = {2022},
isbn = {978-1-939133-29-18},
address = {Carlsbad, CA},
pages = {295--308},
url = {https://www.usenix.org/conference/atc22/presentation/holzbauer},
publisher = {USENIX Association},
month = jul
}

IPv6-Reconnaissance - Internet-weite Analyse von ICMPv6

Florian Holzbauer
Master Thesis, University of Applied Sciences St. Pölten (2020)

Awards

🏆 Netidee Stipend (10.000€) for my doctoral thesis with the title: Measuring the Gap between Standardization, Implementation and Adoption of Internet Standards

BLOG; STIPEND