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CVE-2026-74356 (GCVE-0-2026-74356)

Vulnerability from cvelistv5 – Published: 2026-08-15 05:58 – Updated: 2026-08-17 05:46
VLAI
Title
vhost: fix vhost_get_avail_idx for a non empty ring
Summary
In the Linux kernel, the following vulnerability has been resolved: vhost: fix vhost_get_avail_idx for a non empty ring vhost_get_avail_idx is supposed to report whether it has updated vq->avail_idx. Instead, it returns whether all entries have been consumed, which is usually the same. But not always - in drivers/vhost/net.c and when mergeable buffers have been enabled, the driver checks whether the combined entries are big enough to store an incoming packet. If not, the driver re-enables notifications with available entries still in the ring. The incorrect return value from vhost_get_avail_idx propagates through vhost_enable_notify and causes the host to livelock if the guest is not making progress, as vhost will immediately disable notifications and retry using the available entries. This goes back to commit d3bb267bbdcb ("vhost: cache avail index in vhost_enable_notify()") which changed vhost_enable_notify() to compare the freshly read avail index against vq->last_avail_idx instead of the previously cached vq->avail_idx. Commit 7ad472397667 ("vhost: move smp_rmb() into vhost_get_avail_idx()") then carried over the same comparison when refactoring vhost_enable_notify() to call the unified vhost_get_avail_idx(). The obvious fix is to make vhost_get_avail_idx do what the comment says it does and report whether new entries have been added.
Severity
7.4 (High)
CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: d3bb267bbdcba199568f1325743d9d501dea0560 , < e115471008111f894c6528d9ab2ce7d0ce306f35 (git)
Affected: d3bb267bbdcba199568f1325743d9d501dea0560 , < 7f229d27bf27c7e589eca690d8612763a7a4801f (git)
Affected: d3bb267bbdcba199568f1325743d9d501dea0560 , < a9326b652bc7acd748d7a1143573845c7924d847 (git)
Affected: d3bb267bbdcba199568f1325743d9d501dea0560 , < 09861858a68342f851f71c669ac0f69865c32151 (git)
guessed Create a notification for this product.
Linux Linux Affected: 5.18
Unaffected: 0 , < 5.18 (semver)
Unaffected: 6.12.97 , ≤ 6.12.* (semver)
Unaffected: 6.18.40 , ≤ 6.18.* (semver)
Unaffected: 7.1.5 , ≤ 7.1.* (semver)
Unaffected: 7.2 , ≤ * (original_commit_for_fix)
guessed Create a notification for this product.
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{
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          "product": "Linux",
          "programFiles": [
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            "version": "3.1"
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              "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\u2014only 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\u0027s 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."
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    "datePublished": "2026-08-15T05:58:41.445Z",
    "dateReserved": "2026-08-15T05:44:03.887Z",
    "dateUpdated": "2026-08-17T05:46:17.196Z",
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    "redhat_vex": {
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      "current_release_date": "2026-08-19T07:34:39+00:00",
      "cve": "CVE-2026-74356",
      "id": "CVE-2026-74356",
      "initial_release_date": "2026-08-15T00:00:00+00:00",
      "product_status:known_affected": "198",
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      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: vhost: fix vhost_get_avail_idx for a non empty ring",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-74356.json",
      "version": "3"
    }
  }
}



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Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

Sightings

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Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
  • Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.


Detection rules are retrieved from Rulezet.