CVE-2026-89743 (GCVE-0-2026-89743)

Vulnerability from cvelistv5 – Published: 2026-09-11 19:46 – Updated: 2026-10-19 08:51
VLAI
Title
misc: nsm: bound the device-reported response length
Summary
In the Linux kernel, the following vulnerability has been resolved: misc: nsm: bound the device-reported response length nsm_sendrecv_msg_locked() stores the virtqueue used-ring length reported by the NSM device into msg->resp.len without bounding it to the response buffer. A malicious or buggy backend can report a length larger than the response buffer; parse_resp_raw() then copies that many bytes out of the fixed buffer to user space, disclosing adjacent kernel heap (an out-of-bounds read). The request path already floors its length in fill_req_raw(); the response path lacks the symmetric check. Clamp the stored length to the size of the response buffer. Well-behaved devices report no more than the posted buffer size, so conforming traffic is unaffected.
Severity
7.7 (High)
CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H
Assigner
Linux CNA under the mitre root
CNA scorecard D 53/100 over 6638 records in the last 180 days details
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: b9873755a6c8ccfce79094c4dce9efa3ecb1a749 , < 339f19b9a6171289b0e797deb8bda80b9a1fcc30 (git)
Affected: b9873755a6c8ccfce79094c4dce9efa3ecb1a749 , < 29e634a18957acda11383a15ab98a91c4ae9e294 (git)
Affected: b9873755a6c8ccfce79094c4dce9efa3ecb1a749 , < 2aa0fb9c96f894a9c179a48e7522ea6705800adf (git)
Affected: b9873755a6c8ccfce79094c4dce9efa3ecb1a749 , < 808e530654a5354e6df78863a5d61e4d44e67235 (git)
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Linux Linux Affected: 6.8
Unaffected: 0 , < 6.8 (semver)
Unaffected: 6.12.109 , ≤ 6.12.* (semver)
Unaffected: 6.18.50 , ≤ 6.18.* (semver)
Unaffected: 7.2.4 , ≤ 7.2.* (semver)
Unaffected: 7.3 , ≤ * (original_commit_for_fix)
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          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nmisc: nsm: bound the device-reported response length\n\nnsm_sendrecv_msg_locked() stores the virtqueue used-ring length reported\nby the NSM device into msg-\u003eresp.len without bounding it to the response\nbuffer. A malicious or buggy backend can report a length larger than the\nresponse buffer; parse_resp_raw() then copies that many bytes out of the\nfixed buffer to user space, disclosing adjacent kernel heap (an\nout-of-bounds read). The request path already floors its length in\nfill_req_raw(); the response path lacks the symmetric check.\n\nClamp the stored length to the size of the response buffer. Well-behaved\ndevices report no more than the posted buffer size, so conforming traffic\nis unaffected."
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              "value": "AV:L - A malicious or buggy virtio-nsm backend (hypervisor, QEMU virtio-nsm, or vhost-user device) over-reports the used-ring length consumed by nsm_sendrecv_msg_locked(); the path is local ioctl on /dev/nsm plus virtio, not a network protocol.\nAC:L - The backend deterministically sets the 32-bit used-ring length on each completion, and a local NSM_IOCTL_RAW caller supplies the response iovec that parse_resp_raw() uses as the other copy bound; no race or attacker-uncontrollable layout is required.\nPR:N - The driver registers /dev/nsm as mode 0666 and nsm_dev_ioctl() has no capable() check, so any local process can issue NSM_IOCTL_RAW; a malicious virtio backend also needs no guest credentials.\nUI:N - The attacker opens /dev/nsm and issues NSM_IOCTL_RAW from their own process (the ioctl does not cap response.len to NSM_RESPONSE_MAX_SIZE); no separate victim must mount, click, or otherwise interact.\nS:U - The out-of-bounds read and any resulting oops occur in the guest kernel that hosts the NSM frontend; this is device-to-guest impact, not a guest-to-host, IOMMU, or cross-VM escape.\nC:H - parse_resp_raw() copy_to_user() copies min(user_len, unbounded device len) from the 0x3000-byte resp-\u003edata array, so an over-reported length reads adjacent kmalloc heap and returns that kernel memory to userspace.\nI:N - The oversized copy writes only into the ioctl caller\u0027s userspace buffer; kernel memory is only read, with no out-of-bounds write, use-after-free, or control-flow hijack primitive.\nA:H - A device-chosen length up to 4GiB drives copy_to_user() past the nsm slab object into unmapped or guarded memory, causing a guest kernel oops or panic that can be repeated on every NSM request."
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      "title": "misc: nsm: bound the device-reported response length",
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    "datePublished": "2026-09-11T19:46:49.261Z",
    "dateReserved": "2026-09-11T19:38:34.761Z",
    "dateUpdated": "2026-10-19T08:51:57.186Z",
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            "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nmisc: nsm: bound the device-reported response length\n\nnsm_sendrecv_msg_locked() stores the virtqueue used-ring length reported\nby the NSM device into msg-\u003eresp.len without bounding it to the response\nbuffer. A malicious or buggy backend can report a length larger than the\nresponse buffer; parse_resp_raw() then copies that many bytes out of the\nfixed buffer to user space, disclosing adjacent kernel heap (an\nout-of-bounds read). The request path already floors its length in\nfill_req_raw(); the response path lacks the symmetric check.\n\nClamp the stored length to the size of the response buffer. Well-behaved\ndevices report no more than the posted buffer size, so conforming traffic\nis unaffected."
          }
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      "current_release_date": "2026-11-06T01:22:45+00:00",
      "cve": "CVE-2026-89743",
      "id": "CVE-2026-89743",
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      "product_status:known_affected": "1",
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      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: misc: nsm: bound the device-reported response length",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-89743.json",
      "version": "3"
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}



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