CVE-2026-29643: Improper Check or Handling of Exceptional Conditions

XiangShan (Open-source high-performance RISC-V processor) commit edb1dfaf7d290ae99724594507dc46c2c2125384 (2024-11-28) contains an improper exceptional-condition handling flaw in its CSR subsystem (NewCSR). On affected versions, certain sequences of CSR operations targeting non-existent/custom CSR addresses may trigger an illegal-instruction exception but fail to reliably transfer control to the configured trap handler (mtvec), causing control-flow disruption and potentially leaving the core in a hung or unrecoverable state. This can be exploited by a local attacker able to execute code on the processor to cause a denial of service and potentially inconsistent architectural state.