{"cve":"CVE-2026-63941","nvd":{"published":"2026-07-19T16:17:12.643","modified":"2026-10-22T15:13:51.927","status":"Analyzed","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nKVM: arm64: Correctly cap ZCR_EL2 provided by a guest hypervisor\n\nZCR_EL2 can be updated by a VHE guest hypervisor either using ZCR_EL2\n(which traps) or ZCR_EL1 (which does not trap). KVM handles both in\ndifferent way:\n\n- on ZCR_EL2 trap, ZCR_EL2.LEN is immediately capped at the VM's own\n  VL limit. This has the potential to break existing SW that relies\n  on the full LEN field to be stateful.\n\n- on ZCR_EL1 access, we do absolutely nothing.\n\nOn restoring the SVE context for an L2 guest, we directly restore the\nguest hypervisor's view of ZCR_EL2 into the physical ZCR_EL2. If the\nguest's view of the register was updated using the ZCR_EL2 accessor,\nthe value has already been sanitised (with the caveat mentioned above).\n\nBut if the guest used ZCR_EL1, the raw value is written into the HW,\nand the L2 guest can now access VLs that it shouldn't.\n\nFix all the above by moving the VL capping to the restore points,\nensuring that:\n\n- the HW is always programmed with a capped value, irrespective of\n  the accessor being used,\n\n- the ZCR_EL2.LEN field is always completely stateful, irrespective\n  of the accessor being used.\n\nAdditionally, move ZCR_EL2 to be a sanitised register, ensuring that\nonly the LEN field is actually stateful. This requires some creative\nconstruction of the RES0 mask, as the sysreg generation script does\nnot yet generate RAZ/WI fields.\n\n[maz: rewrote commit message, tidy up access_zcr_el2()]","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H","score":8.8},"cwes":["CWE-862","CWE-20"],"references":["https://git.kernel.org/stable/c/2090c1a2368339eab0e14dcde12fdf6a5ea6359d","https://git.kernel.org/stable/c/742a9b5ccd8c46caf983ca90c94f855466968e34","https://git.kernel.org/stable/c/83726330748981372bde86ed5411d7b306612991"],"products":["linux:linux_kernel"],"source":"nvd","synced_at":"2026-10-22T16:41:11.231219466+00:00"},"epss":{"cve":"CVE-2026-63941","score":0.00149,"percentile":0.04015,"date":"2026-10-25"},"kev":null,"osv":[],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}