{"id":"CVE-2026-74356","state":"PUBLISHED","title":"vhost: fix vhost_get_avail_idx for a non empty ring","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nvhost: fix vhost_get_avail_idx for a non empty ring\n\nvhost_get_avail_idx is supposed to report whether it has updated\nvq->avail_idx. Instead, it returns whether all entries have been\nconsumed, which is usually the same. But not always - in\ndrivers/vhost/net.c and when mergeable buffers have been enabled, the\ndriver checks whether the combined entries are big enough to store an\nincoming packet. If not, the driver re-enables notifications with\navailable entries still in the ring. The incorrect return value from\nvhost_get_avail_idx propagates through vhost_enable_notify and causes\nthe host to livelock if the guest is not making progress, as vhost will\nimmediately disable notifications and retry using the available entries.\n\nThis goes back to commit d3bb267bbdcb (\"vhost: cache avail index in\nvhost_enable_notify()\") which changed vhost_enable_notify() to compare\nthe freshly read avail index against vq->last_avail_idx instead of the\npreviously cached vq->avail_idx. Commit 7ad472397667 (\"vhost: move\nsmp_rmb() into vhost_get_avail_idx()\") then carried over the same\ncomparison when refactoring vhost_enable_notify() to call the unified\nvhost_get_avail_idx().\n\nThe obvious fix is to make vhost_get_avail_idx do what the comment\nsays it does and report whether new entries have been added.","publishedAt":"2026-08-15T05:58:41.445Z","updatedAt":"2026-10-30T12:29:51.074Z","severity":{"score":7.4,"label":"High","version":"3.1","vector":"CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H","source":"Linux"},"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"d3bb267bbdcba199568f1325743d9d501dea0560","status":"affected","lessThan":"7536f8f72bd24f1ae316c24231faaa3667eba837","versionType":"git"},{"version":"d3bb267bbdcba199568f1325743d9d501dea0560","status":"affected","lessThan":"0fe5ca2d56f0122988016e415a074c95925504b7","versionType":"git"},{"version":"d3bb267bbdcba199568f1325743d9d501dea0560","status":"affected","lessThan":"e115471008111f894c6528d9ab2ce7d0ce306f35","versionType":"git"},{"version":"d3bb267bbdcba199568f1325743d9d501dea0560","status":"affected","lessThan":"7f229d27bf27c7e589eca690d8612763a7a4801f","versionType":"git"},{"version":"d3bb267bbdcba199568f1325743d9d501dea0560","status":"affected","lessThan":"a9326b652bc7acd748d7a1143573845c7924d847","versionType":"git"},{"version":"d3bb267bbdcba199568f1325743d9d501dea0560","status":"affected","lessThan":"09861858a68342f851f71c669ac0f69865c32151","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["drivers/vhost/vhost.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"5.18","status":"affected"},{"version":"0","status":"unaffected","lessThan":"5.18","versionType":"semver"},{"version":"6.1.191","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.160","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.97","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.40","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.1.5","status":"unaffected","lessThanOrEqual":"7.1.*","versionType":"semver"},{"version":"7.2","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["drivers/vhost/vhost.c"]}],"references":["https://git.kernel.org/stable/c/7536f8f72bd24f1ae316c24231faaa3667eba837","https://git.kernel.org/stable/c/0fe5ca2d56f0122988016e415a074c95925504b7","https://git.kernel.org/stable/c/e115471008111f894c6528d9ab2ce7d0ce306f35","https://git.kernel.org/stable/c/7f229d27bf27c7e589eca690d8612763a7a4801f","https://git.kernel.org/stable/c/a9326b652bc7acd748d7a1143573845c7924d847","https://git.kernel.org/stable/c/09861858a68342f851f71c669ac0f69865c32151"],"weaknesses":[],"ingestedAt":"2026-10-30T12:48:04.825Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/74xxx/CVE-2026-74356.json","commit":"1f312381e38164a43607eebab851b151dd16861e","baselineCommit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-74356","state":"PUBLISHED","datePublished":"2026-08-15T05:58:41.445Z","dateUpdated":"2026-10-30T12:29:51.074Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-08-15T05:44:03.887Z"},"containers":{"cna":{"title":"vhost: fix vhost_get_avail_idx for a non empty ring","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nvhost: fix vhost_get_avail_idx for a non empty ring\n\nvhost_get_avail_idx is supposed to report whether it has updated\nvq->avail_idx. Instead, it returns whether all entries have been\nconsumed, which is usually the same. But not always - in\ndrivers/vhost/net.c and when mergeable buffers have been enabled, the\ndriver checks whether the combined entries are big enough to store an\nincoming packet. If not, the driver re-enables notifications with\navailable entries still in the ring. The incorrect return value from\nvhost_get_avail_idx propagates through vhost_enable_notify and causes\nthe host to livelock if the guest is not making progress, as vhost will\nimmediately disable notifications and retry using the available entries.\n\nThis goes back to commit d3bb267bbdcb (\"vhost: cache avail index in\nvhost_enable_notify()\") which changed vhost_enable_notify() to compare\nthe freshly read avail index against vq->last_avail_idx instead of the\npreviously cached vq->avail_idx. Commit 7ad472397667 (\"vhost: move\nsmp_rmb() into vhost_get_avail_idx()\") then carried over the same\ncomparison when refactoring vhost_enable_notify() to call the unified\nvhost_get_avail_idx().\n\nThe obvious fix is to make vhost_get_avail_idx do what the comment\nsays it does and report whether new entries have been added."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"d3bb267bbdcba199568f1325743d9d501dea0560","status":"affected","lessThan":"7536f8f72bd24f1ae316c24231faaa3667eba837","versionType":"git"},{"version":"d3bb267bbdcba199568f1325743d9d501dea0560","status":"affected","lessThan":"0fe5ca2d56f0122988016e415a074c95925504b7","versionType":"git"},{"version":"d3bb267bbdcba199568f1325743d9d501dea0560","status":"affected","lessThan":"e115471008111f894c6528d9ab2ce7d0ce306f35","versionType":"git"},{"version":"d3bb267bbdcba199568f1325743d9d501dea0560","status":"affected","lessThan":"7f229d27bf27c7e589eca690d8612763a7a4801f","versionType":"git"},{"version":"d3bb267bbdcba199568f1325743d9d501dea0560","status":"affected","lessThan":"a9326b652bc7acd748d7a1143573845c7924d847","versionType":"git"},{"version":"d3bb267bbdcba199568f1325743d9d501dea0560","status":"affected","lessThan":"09861858a68342f851f71c669ac0f69865c32151","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["drivers/vhost/vhost.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"5.18","status":"affected"},{"version":"0","status":"unaffected","lessThan":"5.18","versionType":"semver"},{"version":"6.1.191","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.160","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.97","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.40","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.1.5","status":"unaffected","lessThanOrEqual":"7.1.*","versionType":"semver"},{"version":"7.2","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["drivers/vhost/vhost.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/7536f8f72bd24f1ae316c24231faaa3667eba837"},{"url":"https://git.kernel.org/stable/c/0fe5ca2d56f0122988016e415a074c95925504b7"},{"url":"https://git.kernel.org/stable/c/e115471008111f894c6528d9ab2ce7d0ce306f35"},{"url":"https://git.kernel.org/stable/c/7f229d27bf27c7e589eca690d8612763a7a4801f"},{"url":"https://git.kernel.org/stable/c/a9326b652bc7acd748d7a1143573845c7924d847"},{"url":"https://git.kernel.org/stable/c/09861858a68342f851f71c669ac0f69865c32151"}],"metrics":[{"cvssV3_1":{"version":"3.1","vectorString":"CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H","baseScore":7.4,"baseSeverity":"HIGH"},"scenarios":[{"lang":"en","value":"AV:A - Exploitation requires a malicious VM guest driving the virtio/vhost-net RX virtqueue on a KVM host; inbound packets cross the adjacent virtual-network boundary into host vhost-net processing, matching kernel CNA precedent for guest-to-host vhost-net bugs.\nAC:L - A guest can deterministically enable mergeable RX buffers, post undersized descriptors, stop refilling, and sustain inbound traffic so handle_rx() repeatedly hits the faulty vhost_enable_notify()/vhost_get_avail_idx() loop without races or rare configs.\nPR:N - A cloud VM tenant or any attacker with code execution inside a vhost-net guest needs no host root, capabilities, or /dev/vhost-net access—only control of the guest virtio RX ring and normal VM networking, which QEMU/KVM provides by default.\nUI:N - No host administrator or victim user action is required beyond standard VM operation; the guest attacker directly manipulates virtio descriptors and can generate or receive the RX traffic that triggers host-side vhost processing.\nS:C - The livelock executes in host kernel vhost worker context while processing guest-controlled virtio ring state, crossing the VM/host isolation boundary and degrading availability for the hypervisor and co-hosted workloads beyond the guest's own scope.\nC:N - This is a pure logic error in available-index comparison causing a notification retry loop; there is no memory corruption, out-of-bounds access, use-after-free, or other primitive that could disclose kernel memory.\nI:N - No kernel memory is corrupted or written beyond the virtio notification state machine; the bug cannot be leveraged for arbitrary write, control-flow hijacking, or code execution on the host.\nA:H - The faulty vhost_enable_notify() loop causes host CPU livelock when the guest stops making progress, pinning a vhost worker at 100% and denying service to the host and other VMs until the offending guest is stopped or killed."}]}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-10-30T12:29:51.074Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.18","versionEndExcluding":"6.1.191"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.18","versionEndExcluding":"6.6.160"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.18","versionEndExcluding":"6.12.97"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.18","versionEndExcluding":"6.18.40"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.18","versionEndExcluding":"7.1.5"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.18","versionEndExcluding":"7.2"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}},"adp":[{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"id":"CVE-2026-74356","role":"CISA Coordinator","options":[{"Exploitation":"none"},{"Automatable":"no"},{"Technical Impact":"partial"}],"version":"2.0.3","timestamp":"2026-10-16T18:54:24.183895Z"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-10-16T18:55:35.157Z"}}]}}}