We have just published Qubes Security Bulletin (QSB) 065: Missed flush in XSA-321 backport (XSA-366). The text of this QSB is reproduced below. This QSB and its accompanying signatures will always be available in the Qubes Security Pack (qubes-secpack).
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---===[ Qubes Security Bulletin 065 ]===--- 2021-02-18 Missed flush in XSA-321 backport (XSA-366) User action required ===================== Users must install the following specific packages in order to address the issues discussed in this bulletin: For Qubes 4.0: - Xen packages, versions 4.8.5-30 For Qubes 4.1: not affected The packages are to be installed in dom0 via the Qube Manager or via the qubes-dom0-update command as follows: For updates from the stable repository (not immediately available): $ sudo qubes-dom0-update For updates from the security-testing repository: $ sudo qubes-dom0-update --enablerepo=qubes-dom0-security-testing A system restart will be required afterwards. These packages will migrate from the security-testing repository to the current (stable) repository over the next two weeks after being tested by the community. If you use Anti Evil Maid, you will need to reseal your secret passphrase to new PCR values, as PCR18+19 will change due to the new Xen binaries. Summary ======== On 2021-02-18, the Xen Security Team published the following Xen Security Advisory (XSA): XSA-366  "missed flush in XSA-321 backport" | An oversight was made when backporting XSA-320, leading entries in the | IOMMU not being properly updated under certain circumstances. Impact ======= XSA-366, as described by the Xen Security Team: | A malicious guest may be able to retain read/write DMA access to | frames returned to Xen's free pool, and later reused for another | purpose. Host crashes (leading to a Denial of Service) and privilege | escalation cannot be ruled out. Credits ======== See the original Xen Security Advisory. References ===========  https://xenbits.xen.org/xsa/advisory-366.html -- The Qubes Security Team https://www.qubes-os.org/security/