{"answers":{"affected":"","exploited":"There is no known exploitation of CVE-2026-99120 in the wild and no public exploit code.","fix":"Upgrade to a fixed version.","what":"CVE-2026-99120 is a vulnerability in Linux, published on 28 Oct 2026."},"fix_prompt":"Check this codebase for CVE-2026-99120 and fix it if it is affected.\n\nWhat it is: CVE-2026-99120 is a vulnerability in Linux, published on 28 Oct 2026. \nExploitation: There is no known exploitation of CVE-2026-99120 in the wild and no public exploit code.\n\nAffected product: Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.\n\nTask:\n1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.\n2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.\n3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.\n4. Run the tests and summarise what changed and why.\n5. If nothing in the project is affected, say so and change nothing.\n\nReference: https://insights.sbomify.com/CVE-2026-99120/ (Markdown: https://insights.sbomify.com/CVE-2026-99120/index.md)","id":"CVE-2026-99120","markdown":"https://insights.sbomify.com/CVE-2026-99120/index.md","name":"CVE-2026-99120","record":{"aliases":["BELL-CVE-2026-99120","DEBIAN-CVE-2026-99120","GHSA-r4wm-h5f5-6qhj","UBUNTU-CVE-2026-99120"],"analysis":null,"analysis_generated_by":null,"assigner":"Linux","cpe":[],"cvss":{"score":null,"severity":null,"source":null,"vector":null,"version":null},"cwes":[],"description":"In the Linux kernel, the following vulnerability has been resolved:\n\nKVM: x86/mmu: Cope with the SS bit being set in #NPF exit codes\n\nWhen running Hyper-V from Windows 11, KVM is seeing the SS bit set\nin nested page fault error codes produced for shadowed NPT.  The AMD\nmanual is unclear about when SS is set, including whether it can be set\nwhen SupervisorShadowStackEn (bit 6) is not set in the MISC_CTL field\nof the VMCB.\n\nNevertheless, the unexpected SS bit causes out of bounds accesses in\npermission_fault(), seen as either WARNs or UBSAN reports:\n\n  kernel: UBSAN: array-index-out-of-bounds in arch/x86/kvm/mmu.h:225:27\n  kernel: index 34 is out of range for type 'u16 [16]'\n\n(in this case, the page fault error code is 34*2=0x44, i.e. SS|U; the\nreport shows SS|U|W happening as well).  Fix the handling of unknown\nerror codes by dropping SS and (with a WARN) any bits not among those\nthat permission_fault() expects to receive.\n\nAt the same time, given the uncertainty about when hardware sets SS,\nfollow the processor's behavior when constructing the fault's error\ncode, and preserve the SS bit as passed to FNAME(walk_addr_generic).\nWhile the behavior is surprising, there's a possibility that Hyper-V\nexpects it (Hyper-V does not even enable CET unless it finds MBEC/GMET!),\nso retain the information when reflecting the fault to L1 instead of\nunconditionally discarding it.\n\nBisection shows that this started happening with commit 687ee95c1b6d (\"KVM:\nnSVM: enable GMET for guests\"), even though SHSTK was available to guests\nsince Linux 6.18.  However, this is not because bit 1 of MISC_CTL (GMET)\nsomehow enables reporting the SS bit; rather, it's simply that Hyper-V\nnever uses CET unless GMET is also present.  The WARN is reproducible\neven with gmet=0, with some hacking of kvm-unit-tests's cet.c testcase\nto ensure that the first access to the shadow stack triggers a page fault.","ecosystems":[],"exploits":{"exploitdb":0,"first_seen":null,"github_poc":0,"max_poc_stars":null,"metasploit":0,"nuclei":0,"refs":[],"tier":"none_known"},"has_fix":true,"headline":"KVM: x86/mmu: Cope with the SS bit being set in #NPF exit codes","id":"CVE-2026-99120","indexable":true,"kev":null,"kind":"cve","links":{"ecosystem":null,"product":null,"products":[],"type":null,"year":"2026"},"n_packages":0,"n_references":3,"next":{"headline":"ipv4: avoid divide by zero in fib_rebalance","id":"CVE-2026-99121"},"packages":[],"prev":{"headline":"drm/amdgpu/userq: actually validate userq BOs","id":"CVE-2026-99119"},"products":["Linux"],"published":"2026-10-28","related":[],"sources":[{"class":"attribution","licence":"CVE Terms of Use (MITRE)","name":"CVE List","prefix":"CVE"}],"ssvc":{"automatable":null,"exploitation":null,"technical_impact":null},"state":"PUBLISHED","updated":"2026-10-28","vendors":["Linux"]},"summary":null,"url":"https://insights.sbomify.com/CVE-2026-99120/"}