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CVE-2026-63806

Vulnérabilité élevée dans Linux (Linux)

CVSS 7.1 · Élevée
EPSS 0.2%
Linux•Linux•Versions : <5c87b47374682f69686068ad0a7779365a527b1c, <=6.1.*, <2.6.32, <=6.12.*, <36ff44fb3d89960391e013fb9d91e23dbc48be47, 0, <=7.1.*, <2426c15c1395b7d5ccf1e5025ca898af7f3decb6, <4186c850789906b875a1d263377a4d37c078e317, <5da9b1a87ec7cc3489c27016313524769f12d9e0, 6.1.178, <=5.10.*, <=6.6.*, 6.12.95, <f1edbed787ba67988ed34e0132ca128b052b6ce8, <=6.18.*, 2.6.32, 5.15.212, 6.6.145, 5.10.261, 6.18.38, <bf89e3738480d33cd515b4a18900e8443d40cd2e, <=*, <=5.15.*, 7.1.3, <92fc631b69deb1c7d56aec2663003600799dcd75, d34e6b175e61821026893ec5298cc8e7558df43a, 7.2

Description

In the Linux kernel, the following vulnerability has been resolved: KVM: Replace guest-triggerable BUG_ON() in ioeventfd datamatch with get_unaligned() Drop a BUG_ON() that has been reachable since it was first added, way back in 2009, and instead use get_unaligned() to perform potentially-unaligned accesses. For a given store, KVM x86's emulator tracks the entire value in the destination operand, x86_emulate_ctxt.dst. If the destination is memory, and the target splits multiple pages and/or is emulated MMIO, then KVM handles each fragment independently. E.g. on a page split starting at page offset 0xffc, KVM writes 4 bytes to the first page, then the remaining bytes to the second page, using ctxt->dst as the source for both (with appropriate offsets). If the destination splits a page *and* hits emulated MMIO on the second page, then KVM will complete the write to the first page, then emulate the MMIO access to the second page. If there is a datamatch-enabled ioeventfd at offset 0 of the second page, then KVM will process the remainder of the store as a potential ioeventfd signal. Putting it all together, if the guest emits a store that splits a page starting at page offset N, and the second page has a datamatch-enabled ioeventfd at offset 0, then KVM will check for datamatch using &dst.valptr[N] as the source. Due to dst (and thus dst.valptr) being 32-byte aligned, if N is not aligned to @len, the BUG_ON() fires. E.g. with a 16-byte store at page offset 0xffc, to an ioeventfd of len 8, all initial checks in ioeventfd_in_range() will succeed, and the BUG_ON() fires due to @val being 4-byte aligned, but not 8-byte aligned. ------------[ cut here ]------------ kernel BUG at arch/x86/kvm/../../../virt/kvm/eventfd.c:783! Oops: invalid opcode: 0000 [#1] SMP CPU: 0 UID: 1000 PID: 615 Comm: repro Not tainted 7.1.0-rc2-ff238429d1ea #365 PREEMPT Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015 RIP: 0010:ioeventfd_write+0x6c/0x70 [kvm] Call Trace: <TASK> __kvm_io_bus_write+0x85/0xb0 [kvm] kvm_io_bus_write+0x53/0x80 [kvm] vcpu_mmio_write+0x66/0xf0 [kvm] emulator_read_write_onepage+0x12a/0x540 [kvm] emulator_read_write+0x109/0x2b0 [kvm] x86_emulate_insn+0x4f8/0xfb0 [kvm] x86_emulate_instruction+0x181/0x790 [kvm] kvm_mmu_page_fault+0x313/0x630 [kvm] vmx_handle_exit+0x18a/0x590 [kvm_intel] kvm_arch_vcpu_ioctl_run+0xc81/0x1c90 [kvm] kvm_vcpu_ioctl+0x2d5/0x970 [kvm] __x64_sys_ioctl+0x8a/0xd0 do_syscall_64+0xb7/0x890 entry_SYSCALL_64_after_hwframe+0x4b/0x53 RIP: 0033:0x7f19c931a9bf </TASK> Modules linked in: kvm_intel kvm irqbypass ---[ end trace 0000000000000000 ]--- In a perfect world, the fix would be to simply delete the BUG_ON(), as KVM x86 doesn't perform alignment checks on "normal" memory accesses at CPL0. Sadly, C99 ruins all the fun; while the x86 architecture plays nice, dereferencing an unaligned pointer directly is undefined behavior in C, e.g. triggers splats when running with CONFIG_UBSAN_ALIGNMENT=y.

Gravité et risque d'exploitation

CVE-2026-63806 obtient un score CVSS de 7.1/10, soit une gravité élevée. Selon le modèle EPSS, la probabilité qu'elle soit exploitée dans les 30 prochains jours est de 0.15 %, ce qui la place devant 4.2 % des CVE référencées.

Que faire ?

  • Vérifiez si Linux (versions <5c87b47374682f69686068ad0a7779365a527b1c, <=6.1.*, <2.6.32, <=6.12.*, <36ff44fb3d89960391e013fb9d91e23dbc48be47, 0, <=7.1.*, <2426c15c1395b7d5ccf1e5025ca898af7f3decb6, <4186c850789906b875a1d263377a4d37c078e317, <5da9b1a87ec7cc3489c27016313524769f12d9e0, 6.1.178, <=5.10.*, <=6.6.*, 6.12.95, <f1edbed787ba67988ed34e0132ca128b052b6ce8, <=6.18.*, 2.6.32, 5.15.212, 6.6.145, 5.10.261, 6.18.38, <bf89e3738480d33cd515b4a18900e8443d40cd2e, <=*, <=5.15.*, 7.1.3, <92fc631b69deb1c7d56aec2663003600799dcd75, d34e6b175e61821026893ec5298cc8e7558df43a, 7.2) est présent sur votre parc.
  • Appliquez le correctif ou la version corrigée indiqués dans les références de l'éditeur.
  • À défaut de correctif, limitez l'exposition (filtrage réseau, désactivation du composant).
  • Automatisez la détection : les agents CVE Heimdall (gratuits, open source) corrèlent l'inventaire de vos serveurs avec la base CVE.

Références

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