Branch Target Reuse: Spectre-v2 Attacks in JIT Engines
Summary
This article reveals Branch Target Reuse (BTR), a Spectre-v2 attack that exploits stale indirect branch prediction entries in JIT engines across browsers, language runtimes, and the Linux kernel. It provides end-to-end exploit demonstrations, discusses affected components (cBPF, SpiderMonkey, GraalVM) and outlines mitigations and CVEs (CVE-2026-64507, CVE-2026-64508).