Key-value stores typically leave access control to the systems for which they act as storage engines. Unfortunately, attackers may circumvent such read access controls via timing attacks on the key-value store, which use differences in query response times to glean information about stored data. To date, key-value store timing attacks have aimed to dis- close stored values and have exploited external mechanisms that can be disabled for protection. In this paper, we point out that key disclosure is also a security threat—and demonstrate key disclosure timing attacks that exploit mechanisms of the key-value store itself. We target LSM-tree based key-value stores utilizing range filters, which have been recently proposed to optimize LSM- tree range queries. We analyze the impact of the contemporary range filters SuRF and Rosetta on LSM-trees through a security lens, and show that they enable a key disclosure timing attack, which we call prefix siphoning. Prefix siphoning successfully leverages benign queries for non-present keys to identify prefixes of actual keys—and in some cases, full keys—in scenarios where brute force searching for keys (via exhaustive enumeration or random guesses) is infeasible.