Hope of Delivery: Extracting User Locations From Mobile Instant Messengers

Theodor Schnitzler, Katharina Kohls, Evangelos Bitsikas, Christina Pöpper

Research output: Chapter in Book/Report/Conference proceedingConference contribution


—Mobile instant messengers such as WhatsApp use delivery status notifications in order to inform users if a sent message has successfully reached its destination. This is useful and important information for the sender due to the often asynchronous use of the messenger service. However, as we demonstrate in this paper, this standard feature opens up a timing side channel with unexpected consequences for user location privacy. We investigate this threat conceptually and experimentally for three widely spread instant messengers. We validate that this information leak even exists in privacy-friendly messengers such as Signal and Threema. Our results show that, after a training phase, a messenger user can distinguish different locations of the message receiver. Our analyses involving multiple rounds of measurements and evaluations show that the timing side channel persists independent of distances between receiver locations – the attack works both for receivers in different countries as well as at small scale in one city. For instance, out of three locations within the same city, the sender can determine the correct one with more than 80 % accuracy. Thus, messenger users can secretly spy on each others’ whereabouts when sending instant messages. As our countermeasure evaluation shows, messenger providers could effectively disable the timing side channel by randomly delaying delivery confirmations within the range of a few seconds. For users themselves, the threat is harder to prevent since there is no option to turn off delivery confirmations.

Original languageEnglish (US)
Title of host publication30th Annual Network and Distributed System Security Symposium, NDSS 2023
PublisherThe Internet Society
ISBN (Electronic)1891562835, 9781891562839
StatePublished - 2023
Event30th Annual Network and Distributed System Security Symposium, NDSS 2023 - San Diego, United States
Duration: Feb 27 2023Mar 3 2023

Publication series

Name30th Annual Network and Distributed System Security Symposium, NDSS 2023


Conference30th Annual Network and Distributed System Security Symposium, NDSS 2023
Country/TerritoryUnited States
CitySan Diego

ASJC Scopus subject areas

  • Computer Networks and Communications
  • Control and Systems Engineering
  • Safety, Risk, Reliability and Quality

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