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TSA-Fill in AMD Zen 5 Processors
TSA-Fill is a Transient Scheduler Attack variant affecting AMD Zen 5 processors. It can allow attacker-controlled code to infer data belonging to other execution contexts, including active memory content of another guest virtual machine on the same physical host. All Xen versions running on affected processors are affected. The vulnerability is tracked under AMD security bulletin AMD-SB-3055 and is distinct from TSA-SQ and TSA-L1, which retain their existing CVE identifiers.
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 compromise confidentiality across execution-context and virtual-machine isolation boundaries. A malicious guest VM, including a Qubes OS qube, may infer sensitive data from another VM sharing the affected host. Direct arbitrary memory writes, host code execution, privilege escalation, or availability impact are not established for TSA-Fill.
If you can’t patch tonight, do this now.
XSA-525 identifies no standalone mitigation. Updated AMD microcode and applicable software fixes are required.
Patch, then assume compromise.
Install updated AMD microcode and the corresponding hypervisor or operating-system security updates. Applicable Zen 5 microcode has been included in linux-firmware since September 23, 2026; obtain supported updates through the operating-system or hardware vendor. Xen administrators should apply the appropriate XSA-525 patch series for their supported branch. Qubes OS 4.3 users should install Xen packages version 4.19.6-4 or later and restart dom0; Anti Evil Maid users must also reseal their secret passphrase after the Xen update. XenServer 8.4 and 9 users should install the latest security updates containing AMD microcode and corresponding product changes. Oracle Linux 9 updates are covered by ELSA-2026-500588 and ELSA-2026-500590, but exact fixed package versions are not available. When deploying the combined XSA-525 fixes, reboot guest VMs to recognize the corrected TSA-SQ/L1 vulnerability status; migration alone is insufficient for that related correction.
No public exploits tracked yet. Mallory keeps watching.
11 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.