In the Linux kernel, the following vulnerability has been resolved:
KVM: arm64: Correctly cap ZCR_EL2 provided by a guest hypervisor
ZCR_EL2 can be updated by a VHE guest hypervisor either using ZCR_EL2
(which traps) or ZCR_EL1 (which does not trap). KVM handles both in
different way:
- on ZCR_EL2 trap, ZCR_EL2.LEN is immediately capped at the VM's own
VL limit. This has the potential to break existing SW that relies
on the full LEN field to be stateful.
- on ZCR_EL1 access, we do absolutely nothing.
On restoring the SVE context for an L2 guest, we directly restore the
guest hypervisor's view of ZCR_EL2 into the physical ZCR_EL2. If the
guest's view of the register was updated using the ZCR_EL2 accessor,
the value has already been sanitised (with the caveat mentioned above).
But if the guest used ZCR_EL1, the raw value is written into the HW,
and the L2 guest can now access VLs that it shouldn't.
Fix all the above by moving the VL capping to the restore points,
ensuring that:
- the HW is always programmed with a capped value, irrespective of
the accessor being used,
- the ZCR_EL2.LEN field is always completely stateful, irrespective
of the accessor being used.
Additionally, move ZCR_EL2 to be a sanitised register, ensuring that
only the LEN field is actually stateful. This requires some creative
construction of the RES0 mask, as the sysreg generation script does
not yet generate RAZ/WI fields.
[maz: rewrote commit message, tidy up access_zcr_el2()]
What the EG score is made of (scorer v4.0: the three questions the 0–10 score mixes, published apart · methodology)
The EG score (8.8): severity, escalated by confirmed exploitation. This CVE's 8.8 is its impact severity (EG Severity), not escalated.
- EG Severity
- 8.8 HIGHCVSS-B, impact only: no KEV listing, EPSS or EG-KEV tier raises it.GitHub Security Advisory CVSS
- EG Likelihood
- 0.2% within 30 daysSource: FIRST EPSS (model v2026.06.15, score date 2026-10-19). FIRST's exploitation probability, not an EchelonGraph model.
- Confirmed exploitation
- None on record (CISA KEV, EG-KEV Tier 1)Reported apart from the likelihood: an observed fact, not a probability.
- EG Priority
- SSVC Track at medium mission impactTrack at low or medium mission impact; Track* at high (mission-essential systems).CISA BOD 26-04: 14 days if the affected system is publicly exposed; Fix on system upgrade if it is not.Each input and its source: the SSVC and BOD 26-04 blocks below.
SSVC (CISA's decision table, applied by EchelonGraph)Track at low or medium mission impact; Track* at high (mission-essential systems).
A fix is available. Apply it within your standard update timelines.
Exploitation none (CISA Vulnrichment) · Automatable no (CISA Vulnrichment) · Technical impact total (CISA Vulnrichment). All three are CISA's SSVC values (Vulnrichment). EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE. Mission impact is CISA's Mission & Well-being decision point, and only you can judge it. CISA's table makes it high when Mission Prevalence is Essential — the vulnerable component "directly provides capabilities that constitute at least one MEF for at least one entity" (MEF: mission essential function) — or when Public Well-Being Impact is Irreversible: "multiple fatalities are likely", the cyber-physical system "is likely lost or destroyed", "extreme or serious externalities" are imposed on other parties, or social systems such as elections or the financial grid "are destabilized and potentially collapse". CISA's decision table
BOD 26-04 (CISA's remediation timeline, Table 1)14 days if the affected system is publicly exposed; Fix on system upgrade if it is not.
In CISA KEV no (CISA's KEV catalog) · Automatable no (CISA Vulnrichment) · Technical impact total (CISA Vulnrichment). Whether your system is publicly exposed is yours to answer. BOD 26-04 binds US Federal Civilian Executive Branch agencies; for anyone else it is CISA's published timeline, a reference rather than an obligation. The directive · how EchelonGraph applies it