New Attack Leverages HTTP/2 for Effective Remote Timing Side-Channel Leaks

Security researchers have outlined a new technique that renders a remote timing-based side-channel attack more effective regardless of the network congestion between the adversary and the target server.

Remote timing attacks that work over a network connection are predominantly affected by variations in network transmission time (or jitter), which, in turn, depends on the load of the network connection at any given point in time.

But since measuring the time taken to execute cryptographic algorithms is crucial to carrying out a timing attack and consequently leak information, the jitter on the network path from the attacker to the server can make it impractical to successfully exploit timing side-channels that rely on a small difference in execution time.

The new method, called Timeless Timing Attacks (TTAs) by researchers from DistriNet Research Group and New York University Abu Dhabi, instead leverages multiplexing of network protocols and concurrent execution by applications, thus making the attacks immune to network conditions.

“These concurrency-based timing attacks infer a relative timing difference by analyzing the order in which responses are returned, and thus do not rely on any absolute timing information,” the researchers said.

Using HTTP/2’s Request Multiplexing to Reduce Jitter

Unlike the typical timing-based attacks, wherein the execution times are measured independently and sequentially, the latest technique attempts to extract information from the order and the relative timing difference between two concurrently executed requests without relying on any timing information.

To do so, a bad actor initiates a pair of HTTP/2 requests to the victim server either directly or using a cross-site — such as a malicious advertisement or tricking the victim into visiting an attacker-controlled web page — to launch requests to the server via JavaScript code.