Researchers from Germany’s Helmholtz Center for Information Security discovered that Loongson processors contain cache leaks that allow data extraction from other applications or the operating system, even within virtual machines.

Loongson designs its own LoongArch instruction set, which blends elements of MIPS and RISC‑V, and ships chips for PCs, servers, and appliances. The company promotes domestic use to reduce reliance on imported technology.

The team used a fuzzer to identify the issue and noted that the LoongArch manual describes an instruction that leaves 32 bits of a memory register in an “uncertain” state. Their analysis showed the uncertainty stems from the L1 data cache, which is shared across applications and not isolated. Because the cache is not isolated, the leak can expose data from other processes or the kernel. An attacker can prime the CPU’s internal state to target a specific cache set, enabling precise data retrieval.

The researchers demonstrated recovery of full‑disk AES keys, partial root password hashes, and bypass of ASLR and stack canaries in seconds. The flaw can be exploited from unprivileged user space, containers, or virtual machines, and can cross the virtual machine boundary to leak host data. The vulnerability is architectural, requiring no high‑resolution timers or side‑channel amplification, and grants the attacker control over cache set and line offset.

Software mitigations are not feasible; the only practical remedies are replacing the chips or ensuring private data never resides in the L1 cache, which may require disabling hyperthreading per core. Loongson addressed the issue in an update to its model 3A6000 processor, with the mitigation incurring a performance reduction of about 1.4 percent in the worst case. Loongson chips are primarily used within China, limiting the broader impact, but they are employed in personal computers, servers, and devices such as printers. Lenovo sells laptops with Loongson chips only in the Chinese market, and other PC manufacturers have indicated they would consider adoption only if demand arises locally. The Chinese government has encouraged domestic chip usage, potentially placing public‑sector devices at risk, and the researchers have found no specific detection tools for the exploit.

The fix reduces performance modestly, and the limited deployment of Loongson chips may constrain the overall risk, but the architectural nature of the flaw means affected systems remain vulnerable unless hardware is replaced.