Processors manufactured by China's Loongson contain a vulnerability in their caches that attackers can exploit to extract sensitive information, even from inside a guest virtual machine, according to researchers from Germany's Helmholtz Center for Information Security. The team discovered the flaw using a fuzzer and detailed their findings on a dedicated website called LoongLeakAttack.com. Loongson has built its own LoongArch instruction set architecture that combines elements from MIPS and RISC-V approaches.
The security team identified that the LoongArch manual references an instruction leaving 32 bits of a memory register in what it calls an "uncertain" state, and their examination showed this uncertain data comes from the L1 data cache under specific conditions. Because this cache isn't isolated between applications, the vulnerability can leak information from other applications and the operating system. An attacker can manipulate the CPU's internal state to direct the leakage toward a particular cache set. Case studies conducted by the researchers demonstrated recovery of complete full-disk AES keys from the kernel, partial root password hashes from user-space, and circumvention of traditional software defenses including ASLR and stack canaries, all accomplished within seconds.
The four researchers—Lorenz Hetterich, Tristan Hornetz, Fabian Thomas, and Michael Schwarz—write in their paper that "LoongLeak can be exploited from unprivileged user space, containers, or virtual machines." They also note the flaw can "cross the virtual machine boundary and leak host data from inside a VM." Because the leakage is architectural in nature, it doesn't require high-resolution timers or conventional side-channel amplification, and it gives attackers precise control over cache set and line offset, according to the research.
Software mitigations aren't feasible for this vulnerability. Users running affected chips must either replace the hardware or ensure no private data enters or stays in the L1 cache, which can require disabling one thread per core and effectively turning off hyperthreading. Loongson did fix the issue in an updated version of its model 3A6000 processor, and the mitigation that evicts cache data reduces performance by just 1.4 percent in the worst-case scenario. The company produces chips for PCs, servers, and devices such as printers, and China's government encourages adoption of Loongson processors as part of its strategy to cut reliance on imported technology.
The impact of this flaw will likely remain contained because Loongson chips see minimal use outside China. Lenovo manufactures laptops using Loongson processors but only markets them domestically, and no non-Chinese company has adopted the chips despite major PC-makers telling The Register they'd consider the products if customer demand materialized or if market participation in China required it. Chinese government agencies that bought local products following Beijing's instructions to public sector purchasers may be operating vulnerable systems, but the researchers found no specific tools or methods exist to detect whether LoongLeak is being actively exploited. For organizations reliant on hardware supply chains rooted in particular geographies, the disclosure surfaces questions about the visibility available when evaluating chip-level integrity. Dependence on any single vendor's architectural choices creates exposure that software alone can't always remedy.