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CVE-2026-74742 (GCVE-0-2026-74742)

Vulnerability from cvelistv5 – Published: 2026-08-26 14:36 – Updated: 2026-08-27 05:01
VLAI
Title
veth: fix queue index used to wake the peer txq in veth_poll
Summary
In the Linux kernel, the following vulnerability has been resolved: veth: fix queue index used to wake the peer txq in veth_poll veth_poll() derives the index of the peer TX queue to wake from rq->xdp_rxq.queue_index. That field is only initialized by xdp_rxq_info_reg() in veth_enable_xdp_range(), which runs only when an XDP program is attached. On the plain GRO/NAPI path (veth_napi_enable_range()) xdp_rxq_info_reg() is never called, so queue_index stays 0 for every queue, as priv->rq is zero-allocated. So in a multi-queue setup with GRO enabled and no XDP program attached, every NAPI instance looks at the peer's TX queue 0. If veth_xmit() stops peer TX queue 1 because the ptr_ring is full (NETDEV_TX_BUSY), nothing ever wakes it again: the poller draining queue 1 wakes queue 0 instead. veth implements no ndo_tx_timeout, so the netdev watchdog does not kick in either, and the queue stays stopped indefinitely. Derive the index from the position of the rq within priv->rq instead, which is correct regardless of whether XDP was ever enabled. Scripts to reproduce the stall are available at https://github.com/netoptimizer/veth-backpressure-performance-testing
Severity
7.5 (High)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 9fe31b3f314534e238aa6d0b6fb492134cbcf8be , < b662a1fb4f3a5ea19bac24eea8315b1d05be51e7 (git)
Affected: dc82a33297fc2c58cb0b2b008d728668d45c0f6a , < 73f8dd22b1e533a99ecc3f9b5de6c6daccaecace (git)
Affected: dc82a33297fc2c58cb0b2b008d728668d45c0f6a , < 90bb11fb29d3c55a2c46dc7c386d096b286e7fcf (git)
Affected: dc82a33297fc2c58cb0b2b008d728668d45c0f6a , < 60db47f02bfa2aa688938aa199117ec4f8e31d23 (git)
Affected: 6.12.61 , < 6.12.105 (semver)
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Linux Linux Affected: 6.16
Unaffected: 0 , < 6.16 (semver)
Unaffected: 6.12.105 , ≤ 6.12.* (semver)
Unaffected: 6.18.46 , ≤ 6.18.* (semver)
Unaffected: 7.1.10 , ≤ 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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      "affected": [
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          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "drivers/net/veth.c"
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          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nveth: fix queue index used to wake the peer txq in veth_poll\n\nveth_poll() derives the index of the peer TX queue to wake from\nrq-\u003exdp_rxq.queue_index. That field is only initialized by\nxdp_rxq_info_reg() in veth_enable_xdp_range(), which runs only when an\nXDP program is attached. On the plain GRO/NAPI path\n(veth_napi_enable_range()) xdp_rxq_info_reg() is never called, so\nqueue_index stays 0 for every queue, as priv-\u003erq is zero-allocated.\n\nSo in a multi-queue setup with GRO enabled and no XDP program attached,\nevery NAPI instance looks at the peer\u0027s TX queue 0. If veth_xmit() stops\npeer TX queue 1 because the ptr_ring is full (NETDEV_TX_BUSY), nothing\never wakes it again: the poller draining queue 1 wakes queue 0 instead.\nveth implements no ndo_tx_timeout, so the netdev watchdog does not kick\nin either, and the queue stays stopped indefinitely.\n\nDerive the index from the position of the rq within priv-\u003erq instead,\nwhich is correct regardless of whether XDP was ever enabled.\n\nScripts to reproduce the stall are available at\nhttps://github.com/netoptimizer/veth-backpressure-performance-testing"
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            "version": "3.1"
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              "value": "AV:N - Remote packets routed, NATed, or bridged into a suitably configured container veth reach veth_xmit() and veth_poll() through normal netdev transmit and NAPI softirq paths; no local syscall or physical access is required.\nAC:L - Sustained multi-flow traffic can deterministically fill the ptr_ring on a non-zero RX queue and drive its NAPI poller; waking queue 0 instead of the stopped queue is a logic bug, not a race or layout-dependent condition the attacker cannot control.\nPR:N - Multi-queue veth, GRO, and a non-noqueue qdisc are infrastructure prerequisites, not attacker privileges; forwarded packets traverse veth_xmit/veth_poll with no capability or authentication check, as with CVE-2025-68232 in the same backpressure code.\nUI:N - Exploitation requires only attacker-generated network traffic to drive backpressure on the veth pair; no victim action such as mounting filesystems or opening files is necessary.\nS:U - The defect leaves transmit queues in DRV_XOFF within the host kernel veth driver and does not cross VM, IOMMU, or sandbox security boundaries.\nC:N - The bug only mis-associates NAPI poll instances with peer TX queue indices during wakeup; there is no out-of-bounds access, use-after-free, or other memory read primitive.\nI:N - No memory corruption, arbitrary write, packet tampering, or control-flow influence occurs; the failure is limited to incorrect queue state management on the transmit path.\nA:H - When a non-zero peer TX queue is stopped for a full ptr_ring, veth_poll() never wakes it again and veth has no ndo_tx_timeout recovery, causing an indefinite transmit stall and persistent loss of connectivity on affected queues."
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        "shortName": "Linux"
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    "cveId": "CVE-2026-74742",
    "datePublished": "2026-08-26T14:36:53.580Z",
    "dateReserved": "2026-08-15T05:44:03.930Z",
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    "redhat_vex": {
      "aggregate_severity": "Moderate",
      "current_release_date": "2026-08-27T09:54:47+00:00",
      "cve": "CVE-2026-74742",
      "id": "CVE-2026-74742",
      "initial_release_date": "2026-08-26T00:00:00+00:00",
      "product_status:known_affected": "14",
      "product_status:known_not_affected": "260",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: veth: fix queue index used to wake the peer txq in veth_poll",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-74742.json",
      "version": "3"
    },
    "suse_vex": {
      "aggregate_severity": "important",
      "current_release_date": "2026-09-03T00:05:37Z",
      "cve": "CVE-2026-74742",
      "id": "CVE-2026-74742",
      "initial_release_date": "2026-09-03T00:05:37Z",
      "product_status:known_not_affected": "353",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2026-74742",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2026-74742.json",
      "version": "2"
    }
  }
}



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