Bitcoin Core reveals bug that made thousands of nodes trust any stranger on Tor
Bitcoin Core disclosed a security flaw that allowed strangers connecting through Tor to bypass spam and privacy protections on thousands of nodes by inheriting permissions intended for trusted computers.
The vulnerability affected nodes that had enabled Bitcoin Core's whitelist setting while also using Tor, a service that hides internet addresses. When incoming Tor connections appeared to come from the local Tor software, and if that software's address fell within a trusted range, outside visitors inherited the permissions meant for trusted computers.
This arrangement led to "thousands of reachable mainnet nodes whitelisting all incoming Tor connections," according to the security advisory published on Tuesday. Nodes that never enabled the whitelist setting were unaffected by this particular flaw.
Other disclosed vulnerabilities
Two additional flaws were also disclosed. A high-severity bug could prevent affected mining nodes from building valid blocks until restarted, occurring when a node handles competing versions of the blockchain. Another medium-severity vulnerability allowed a malicious connection to stall a node's processing of new blocks for 10 minutes, potentially repeatable indefinitely.
Delayed disclosure policy
Bitcoin Core typically publishes details of medium- and high-severity vulnerabilities two weeks after the last affected release goes out of support, giving operators time to install fixes before explanations become available. The delay in these disclosures followed this standard timetable.
Developers changed their policy in October for flaws that are easy to rediscover, including through simple prompts to AI models. Those now receive patched releases and security advisories as soon as possible. Tuesday's disclosures followed the longer timetable.
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