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Researchers from CISPA Helmholtz Center for Information Security and KU Leuven reported that several commercial out-of-order RISC-V processors are vulnerable to major Spectre speculative-execution attacks, challenging assumptions that the architecture was largely resistant to this class of flaws. The affected chips include SiFive P550 and T-Head Xuantie C910/C920, which were found susceptible to Spectre-PHT, Spectre-BTB, Spectre-RSB, and Spectre-STL, while tested in-order processors such as SiFive U74 and Xuantie C906/C908 did not appear vulnerable.
The researchers demonstrated proof-of-concept exploits with up to 100% recall and more than 97% precision, including leakage of arbitrary Linux kernel memory from the Xuantie C910 at 338 bytes per second. They said mitigations developed for x86 and ARM do not transfer cleanly to RISC-V because of limited hardware introspection and ecosystem diversity; following responsible disclosure in December, three Linux patches were merged upstream and both SiFive and T-Head have taken or committed to mitigation steps.
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Researchers from CISPA and KU Leuven said they responsibly disclosed findings that several commercial out-of-order RISC-V processors were vulnerable to major Spectre variants. The disclosure covered affected chips including SiFive P550 and T-Head Xuantie C910/C920.
The researchers demonstrated proof-of-concept Spectre attacks with up to 100 percent recall and more than 97 percent precision, including leakage of arbitrary Linux kernel memory from a T-Head Xuantie C910. The demonstrated leak rate was 338 bytes per second.
Researchers reported that commercial out-of-order RISC-V processors, including SiFive P550 and T-Head Xuantie C910/C920, are vulnerable to Spectre-PHT, Spectre-BTB, Spectre-RSB, and Spectre-STL. Their work concluded that tested in-order chips such as SiFive U74 and Xuantie C906/C908 did not appear vulnerable.
T-Head, part of Alibaba, committed to publishing ad-hoc speculation barriers and otherwise addressing the disclosed Spectre issues in its Xuantie C910/C920 processors. The commitment came after researchers showed the chips were susceptible to major Spectre attacks.
SiFive took mitigation steps to address the Spectre findings affecting its P550 commercial RISC-V processor. This response followed the researchers' disclosure of vulnerabilities to multiple Spectre variants.
Following responsible disclosure, three patches from the researchers were merged into mainline Linux to mitigate the reported Spectre issues on RISC-V. The sources also note that additional patches remained under review.
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Researchers disclosed the **Meltdown** and **Spectre** hardware flaws, showing that speculative execution in modern processors could let attackers read sensitive data across security boundaries on affected devices. Reuters reported that **Meltdown** primarily affected Intel processors by breaking memory isolation, while **Spectre** impacted Intel, AMD, and ARM chips by tricking applications into leaking secrets such as passwords and other protected data. CERT/CC later summarized the broader issue as cache side-channel attacks against CPU hardware using speculative execution, underscoring that the weakness was architectural rather than limited to a single product line. Major vendors and cloud providers moved to contain the fallout with software, firmware, and microcode mitigations, including Microsoft Azure protections for hosted customers and public advisories from manufacturers such as Huawei. Subsequent research showed the problem persisted beyond the initial disclosures: the **ZombieLoad** attacks demonstrated additional Intel data-leakage paths tied to speculative execution, and a later **TSX Asynchronous Abort (TAA)** variant affected some processors previously thought to be resistant. Intel issued microcode updates, but researchers and vendors warned that mitigations reduced rather than eliminated risk, that exploitation generally required local code execution, and that fully disabling the underlying CPU behavior would carry significant performance costs.
Jun 29, 2026
Researchers disclosed the speculative-execution attacks **Meltdown** (`CVE-2017-5754`) and **Spectre** (`CVE-2017-5753`, `CVE-2017-5715`), showing that modern Intel, AMD, and ARM processors could leak sensitive data across privilege boundaries through cache-timing side channels. Google Project Zero demonstrated kernel and virtual-machine memory disclosure, while browser vendors including Mozilla confirmed that web content could abuse similar techniques, prompting Firefox to reduce timer precision and disable `SharedArrayBuffer` by default. Microsoft, Apple, Linux distributors, cloud providers, and hardware vendors issued operating-system, browser, and microcode mitigations, with Microsoft saying Azure had already been updated and Intel later announcing hardware changes for future chips. Early mitigation rollouts brought significant operational concerns, including uneven performance degradation and unstable firmware updates. Linux and macOS testing found that common desktop benchmarks often changed little, but syscall-heavy, storage, and IO-intensive workloads could slow noticeably, with some macOS microbenchmarks degrading by roughly **2x to 4x** and Windows Server or older systems expected to see larger impacts than newer Windows 10 devices. Intel’s early Spectre-related microcode updates were later linked to reboots and possible data corruption, leading Microsoft to publish an emergency update that disabled one mitigation path, while vendors such as Dell and NetApp tracked product exposure and remediation guidance as the industry continued responding to follow-on speculative-execution issues.
Aug 8, 2026
Researchers from MIT CSAIL disclosed an **interrupt injection** attack that can bypass Linux’s `Safe RET` mitigation for Spectre-class attacks on **AMD Zen 1 through Zen 4** processors, potentially allowing information disclosure from kernel memory. AMD acknowledged the issue in its **Return Address Security Bulletin** and said the weakness stems from Linux’s implementation of the mitigation for **Speculative Return Stack Overflow (SRSO)** rather than the processor architecture alone. The flaw lets an attacker with code execution on a target system precisely time an interrupt to disrupt branch predictor sanitization and weaken the intended protection. Linux has already patched the issue in the latest kernel Git code by addressing the handling of interrupts around the `Safe RET` mitigation path. The researchers reported demonstrating arbitrary kernel memory leakage on **AMD Zen 2** systems running Linux with default Spectre v2 defenses, achieving **5.47 bytes per second** at **91.97% accuracy** and reading `/etc/shadow` in five of ten attempts. The work was reported by **Daniël Trujillo** of MIT CSAIL, presented at **Black Hat USA**, and accompanied by a proposed fix that adds a second predictor neutralization step on interrupt return; researchers also said related misprediction behavior was observed on some Intel systems, though AMD is the vendor that formally assigned and documented the vulnerability.
Aug 12, 2026