{"id":"CVE-2026-23086","title":"In the Linux kernel, the following vulnerability has been resolved:\n\nvsock/virtio: cap TX credit to local buffer size\n\nThe virtio transports derives its TX credit directly from peer_buf_alloc,\nwhich is set from the remote endpoint's SO_V…","summary":"In the Linux kernel, the following vulnerability has been resolved:\n\nvsock/virtio: cap TX credit to local buffer size\n\nThe virtio transports derives its TX credit directly from peer_buf_alloc,\nwhich is set from the remote endpoint's SO_V…","severity":"medium","cvss":5.5,"cvssVector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H","vendor":"linux","product":"linux_kernel","affected":["linux_kernel >= 4.8, < 6.1.162","linux_kernel >= 6.2, < 6.6.122","linux_kernel >= 6.7, < 6.12.68","linux_kernel >= 6.13, < 6.18.8","linux_kernel = 6.19"],"patched":["linux_kernel 6.18.8"],"published":"2026-02-04","updated":"2026-10-15","sourceUpdated":"2026-10-15T02:18:41.477","source":"NVD","sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2026-23086","references":[{"url":"https://git.kernel.org/stable/c/84ef86aa7120449828d1e0ce438c499014839711","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/8ee784fdf006cbe8739cfa093f54d326cbf54037","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/c0e42fb0e054c2b2ec4ee80f48ccd256ae0227ce","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/d9d5f222558b42f6277eafaaa6080966faf37676","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/fef7110ae5617555c792a2bb4d27878d84583adf","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://cert-portal.siemens.com/productcert/html/ssa-019113.html","label":"0b142b55-0307-4c5a-b3c9-f314f3fb7c5e"},{"url":"https://cert-portal.siemens.com/productcert/html/ssa-457936.html","label":"0b142b55-0307-4c5a-b3c9-f314f3fb7c5e"}],"tags":["nvd","cve.org"],"epss":0.00167,"epssPercentile":0.05924,"ssvc":{"exploitation":"none","automatable":"no","technicalImpact":"partial","timestamp":"2026-06-10T20:42:20.829487Z"},"ingestedAt":"2026-09-08T15:33:26.993Z","slug":"CVE-2026-23086","body":"## Overview\n\nIn the Linux kernel, the following vulnerability has been resolved:\n\nvsock/virtio: cap TX credit to local buffer size\n\nThe virtio transports derives its TX credit directly from peer_buf_alloc,\nwhich is set from the remote endpoint's SO_VM_SOCKETS_BUFFER_SIZE value.\n\nOn the host side this means that the amount of data we are willing to\nqueue for a connection is scaled by a guest-chosen buffer size, rather\nthan the host's own vsock configuration. A malicious guest can advertise\na large buffer and read slowly, causing the host to allocate a\ncorrespondingly large amount of sk_buff memory.\nThe same thing would happen in the guest with a malicious host, since\nvirtio transports share the same code base.\n\nIntroduce a small helper, virtio_transport_tx_buf_size(), that\nreturns min(peer_buf_alloc, buf_alloc), and use it wherever we consume\npeer_buf_alloc.\n\nThis ensures the effective TX window is bounded by both the peer's\nadvertised buffer and our own buf_alloc (already clamped to\nbuffer_max_size via SO_VM_SOCKETS_BUFFER_MAX_SIZE), so a remote peer\ncannot force the other to queue more data than allowed by its own\nvsock settings.\n\nOn an unpatched Ubuntu 22.04 host (~64 GiB RAM), running a PoC with\n32 guest vsock connections advertising 2 GiB each and reading slowly\ndrove Slab/SUnreclaim from ~0.5 GiB to ~57 GiB; the system only\nrecovered after killing the QEMU process. That said, if QEMU memory is\nlimited with cgroups, the maximum memory used will be limited.\n\nWith this patch applied:\n\n  Before:\n    MemFree:        ~61.6 GiB\n    Slab:           ~142 MiB\n    SUnreclaim:     ~117 MiB\n\n  After 32 high-credit connections:\n    MemFree:        ~61.5 GiB\n    Slab:           ~178 MiB\n    SUnreclaim:     ~152 MiB\n\nOnly ~35 MiB increase in Slab/SUnreclaim, no host OOM, and the guest\nremains responsive.\n\nCompatibility with non-virtio transports:\n\n  - VMCI uses the AF_VSOCK buffer knobs to size its queue pairs per\n    socket based on the local vsk->buffer_* values; the remote side\n    cannot enlarge those queues beyond what the local endpoint\n    configured.\n\n  - Hyper-V's vsock transport uses fixed-size VMBus ring buffers and\n    an MTU bound; there is no peer-controlled credit field comparable\n    to peer_buf_alloc, and the remote endpoint cannot drive in-flight\n    kernel memory above those ring sizes.\n\n  - The loopback path reuses virtio_transport_common.c, so it\n    naturally follows the same semantics as the virtio transport.\n\nThis change is limited to virtio_transport_common.c and thus affects\nvirtio-vsock, vhost-vsock, and loopback, bringing them in line with the\n\"remote window intersected with local policy\" behaviour that VMCI and\nHyper-V already effectively have.\n\n[Stefano: small adjustments after changing the previous patch]\n[Stefano: tweak the commit message]\n\n## Affected\n\n- `linux_kernel >= 4.8, < 6.1.162`\n- `linux_kernel >= 6.2, < 6.6.122`\n- `linux_kernel >= 6.7, < 6.12.68`\n- `linux_kernel >= 6.13, < 6.18.8`\n- `linux_kernel = 6.19`\n\n## Remediation\n\nUpgrade past the affected range:\n\n- `linux_kernel 6.18.8`","depth":"sunlit","depthScore":30,"depthScoreParts":{"impact":30.3,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[{"seq":221621,"id":"CVE-2026-23086","ts":1792035291971,"field":"cvss","old":null,"new":"5.5"},{"seq":221620,"id":"CVE-2026-23086","ts":1792035291971,"field":"severity","old":"none","new":"medium"}]}