AEGLIX vulnerability intelligence
CVE-2026-99120
UNSCORED · Received
Published: 2026-10-28 · Updated: 2026-10-28 · Source: NVD
Stored catalog record
Source record retrieved 2026-10-28T13:51:06.633592+00:00. Scheduled imports handle updates; this page does not assert that the provider was queried just now.
Vulnerability overview
In the Linux kernel, the following vulnerability has been resolved: KVM: x86/mmu: Cope with the SS bit being set in #NPF exit codes When running Hyper-V from Windows 11, KVM is seeing the SS bit set in nested page fault error codes produced for shadowed NPT. The AMD manual is unclear about when SS is set, including whether it can be set when SupervisorShadowStackEn (bit 6) is not set in the MISC_CTL field of the VMCB. Nevertheless, the unexpected SS bit causes out of bounds accesses in permission_fault(), seen as either WARNs or UBSAN reports: kernel: UBSAN: array-index-out-of-bounds in arch/x86/kvm/mmu.h:225:27 kernel: index 34 is out of range for type 'u16 [16]' (in this case, the page fault error code is 34*2=0x44, i.e. SS|U; the report shows SS|U|W happening as well). Fix the handling of unknown error codes by dropping SS and (with a WARN) any bits not among those that permission_fault() expects to receive. At the same time, given the uncertainty about when hardware sets SS, follow the processor's behavior when constructing the fault's error code, and preserve the SS bit as passed to FNAME(walk_addr_generic). While the behavior is surprising, there's a possibility that Hyper-V expects it (Hyper-V does not even enable CET unless it finds MBEC/GMET!), so retain the information when reflecting the fault to L1 instead of unconditionally discarding it. Bisection shows that this started happening with commit 687ee95c1b6d ("KVM: nSVM: enable GMET for guests"), even though SHSTK was available to guests since Linux 6.18. However, this is not because bit 1 of MISC_CTL (GMET) somehow enables reporting the SS bit; rather, it's simply that Hyper-V never uses CET unless GMET is also present. The WARN is reproducible even with gmet=0, with some hacking of kvm-unit-tests's cet.c testcase to ensure that the first access to the shadow stack triggers a page fault.
Patch review priority
Assess exposure and vendor guidance
- No higher-priority signal is available in the current stored evidence.
- Fresh EPSS data is unavailable; missing values are not zero.
EPSS unavailable; no zero score is assumed.
EPSS estimates probability of exploitation in the next 30 days. It does not measure your exposure or prove exploitation. The elevated threshold is 10%; CISA KEV takes precedence. About FIRST EPSS ↗
Severity and scoring
- CVSS score
- Not scored · UNSCORED
- CVSS version
- Not supplied
- CVSS vector
- Not supplied
- Weaknesses
- Not supplied
CVSS measures technical severity; it does not establish whether this vulnerability is being exploited in your environment.
Known exploitation and remediation
Not listed in the CISA catalog retrieved for this record. This does not establish that exploitation has not occurred.
Verify affected versions and patch availability in the vendor advisory before making changes.
Affected products and versions
NVD has not supplied affected-version configurations for this record. Check the vendor references below.