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AMD Floating Point Divider State Sampling (FPDSS)
Floating Point Divider State Sampling is a transient-execution vulnerability in certain AMD processors, including affected Zen 1 and Zen+ models. The floating-point divider does not properly clear internal data during speculative execution and can retain partial quotient data from previous operations. A local attacker executing unprivileged code may sample this residual state to infer sensitive information. In virtualized environments, code in one guest VM may infer floating-point division operands from another VM. The flaw resides in CPU hardware rather than Xen, XenServer, or XCP-ng software.
What it means and what to do now: patch path, interim mitigations, and the assume-compromise checklist.
What an attacker gets, and what they’ve been doing with it.
Successful exploitation can disclose sensitive information processed by the floating-point divider, compromising confidentiality and potentially breaching isolation between guest VMs sharing affected hardware. The identified impact is information disclosure; code execution, privilege escalation, and denial of service are not established for this vulnerability.
If you can’t patch tonight, do this now.
Pending updates, restrict untrusted local code execution and avoid placing untrusted workloads on affected AMD hardware where practical. No separate temporary XenServer workaround is specified; its security updates supply the hardware-vulnerability mitigation.
Patch, then assume compromise.
Install operating-system or hypervisor updates that implement mitigation for CVE-2025-54505. Update XenServer 8.4 to the latest available release in the Normal or Early Access update channel. For XCP-ng 8.3 LTS, install xen-4.17.6-6.2.xcpng8.3 or later. Debian fixes include Xen 4.17.7-0+deb12u1 for Debian 12 and 4.20.3+127-gc42374a105-0+deb13u1 for Debian 13. On affected Ubuntu deployments, install the applicable vendor kernel security updates and reboot to activate them.
No validated public exploits yet. Hidden: 1 rejected by Mallory's analysis as not a working exploit.
20 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.