https://www.bleepingcomputer.com/news/security/o2-uk-patches-bug-leaking-mobile-user-location-from-call-metadata/
… The problem was discovered by security researcher Daniel Williams, who says the flaw existed on O2 UK’s network since March 27, 2017, and was resolved yesterday. …However, as Williams discovered while analyzing the traffic during such a call, the signalling messages (SIP Headers) exchanged between the communicating parties are far too verbose and revealing, including IMSI, IMEI, and cell location data. …
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