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auxdisplay: line-display: fix OOB read on zero-length message_store()

Type: advisorySources: OSV

In the Linux kernel, the following vulnerability has been resolved: auxdisplay: line-display: fix OOB read on zero-length message_store() linedisp_display() unconditionally reads msg[count - 1] before checking whether count is zero, so a write of zero bytes to the message sysfs attribute hits msg[-1]: write(fd, "", 0); -> message_store(..., buf, count=0) -> linedisp_display(linedisp, buf, count=0) -> msg[count - 1] == '\n' ; OOB read The kernfs write buffer for that store is a 1-byte allocation (kernfs_fop_write_iter() does kmalloc(len + 1) with len == 0), so msg[-1] is a 1-byte read before the slab object. On a KASAN-enabled kernel this trips an out-of-bounds report and panics; on stock kernels it silently reads adjacent slab data and, if that byte happens to be '\n', the following count-- wraps ssize_t 0 to -1 and is then passed to kmemdup_nul(). linedisp_display() is reached from the message_store() sysfs callback (drivers/auxdisplay/line-display.c message attribute, mode 0644) and from the in-tree initial-message setup with count == -1, so the OOB path is only userspace-triggerable via zero-byte writes; vfs_write() does not short-circuit on count == 0 and kernfs_fop_write_iter() dispatches the store callback regardless. Guard the trailing-newline trim with a count check. The existing if (!count) block then takes the clear-display path unchanged. Affects every auxdisplay driver that registers via linedisp_register() / linedisp_attach(): ht16k33, max6959, img-ascii-lcd, seg

Products
Kernel
Affected versions
Not specified
Fixed versions
6.1.176, 6.12.93, 6.18.35, 6.6.143, 7.0.12
CVEs
CVE-2026-63949
Confirmed fixed CVEs
Not specified
Updated in this feed
8 Nov 2026, 01:24 UTC · Revision 1

Source evidence

auxdisplay: line-display: fix OOB read on zero-length message_store()

core-osv · Original source

Published 19 Jul 2026, 14:55 UTC

In the Linux kernel, the following vulnerability has been resolved: auxdisplay: line-display: fix OOB read on zero-length message_store() linedisp_display() unconditionally reads msg[count - 1] before checking whether count is zero, so a write of zero bytes to the message sysfs attribute hits msg[-1]: write(fd, "", 0); -> message_store(..., buf, count=0) -> linedisp_display(linedisp, buf, count=0) -> msg[count - 1] == '\n' ; OOB read The kernfs write buffer for that store is a 1-byte allocation (kernfs_fop_write_iter() does kmalloc(len + 1) with len == 0), so msg[-1] is a 1-byte read before the slab object. On a KASAN-enabled kernel this trips an out-of-bounds report and panics; on stock kernels it silently reads adjacent slab data and, if that byte happens to be '\n', the following count-- wraps ssize_t 0 to -1 and is then passed to kmemdup_nul(). linedisp_display() is reached from the message_store() sysfs callback (drivers/auxdisplay/line-display.c message attribute, mode 0644) and from the in-tree initial-message setup with count == -1, so the OOB path is only userspace-triggerable via zero-byte writes; vfs_write() does not short-circuit on count == 0 and kernfs_fop_write_iter() dispatches the store callback regardless. Guard the trailing-newline trim with a count check. The existing if (!count) block then takes the clear-display path unchanged. Affects every auxdisplay driver that registers via linedisp_register() / linedisp_attach(): ht16k33, max6959, img-ascii-lcd, seg

osv:CVE-2026-63949

Kernel

Fixed versions: 6.1.176, 6.6.143, 6.12.93, 6.18.35, 7.0.12

Complete source record
{
  "id": "2065c4acbfda3600fa3db3b9f2e310047489309d62d6e877181897af8332ab3a",
  "url": "https://osv.dev/vulnerability/CVE-2026-63949",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "auxdisplay: line-display: fix OOB read on zero-length message_store()",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: auxdisplay: line-display: fix OOB read on zero-length message_store() linedisp_display() unconditionally reads msg[count - 1] before checking whether count is zero, so a write of zero bytes to the message sysfs attribute hits msg[-1]: write(fd, \"\", 0); -> message_store(..., buf, count=0) -> linedisp_display(linedisp, buf, count=0) -> msg[count - 1] == '\\n' ; OOB read The kernfs write buffer for that store is a 1-byte allocation (kernfs_fop_write_iter() does kmalloc(len + 1) with len == 0), so msg[-1] is a 1-byte read before the slab object. On a KASAN-enabled kernel this trips an out-of-bounds report and panics; on stock kernels it silently reads adjacent slab data and, if that byte happens to be '\\n', the following count-- wraps ssize_t 0 to -1 and is then passed to kmemdup_nul(). linedisp_display() is reached from the message_store() sysfs callback (drivers/auxdisplay/line-display.c message attribute, mode 0644) and from the in-tree initial-message setup with count == -1, so the OOB path is only userspace-triggerable via zero-byte writes; vfs_write() does not short-circuit on count == 0 and kernfs_fop_write_iter() dispatches the store callback regardless. Guard the trailing-newline trim with a count check. The existing if (!count) block then takes the clear-display path unchanged. Affects every auxdisplay driver that registers via linedisp_register() / linedisp_attach(): ht16k33, max6959, img-ascii-lcd, seg",
    "evidence": "osv:CVE-2026-63949",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "6.1.176",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.6.143",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.12.93",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.18.35",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "7.0.12",
            "evidence": "/affected/1/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "unknown",
    "structured": {
      "id": "CVE-2026-63949",
      "aliases": [
        "CVE-2026-63949"
      ],
      "affected": [
        {
          "ranges": [
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              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
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                {
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                {
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                {
                  "fixed": "6ad4f75ef9f3372fce8cad494e789ac6a5507bef"
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                {
                  "fixed": "a7511dcd9dd4bc55d123f9b800c8a4ed2662e5c6"
                }
              ]
            }
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-63949.json"
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        },
        {
          "ranges": [
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "5.16.0"
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            {
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                {
                  "introduced": "6.2.0"
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                {
                  "fixed": "6.6.143"
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            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.7.0"
                },
                {
                  "fixed": "6.12.93"
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              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.13.0"
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                {
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            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
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          ],
          "package": {
            "name": "Kernel",
            "ecosystem": "Linux"
          },
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-63949.json"
          }
        }
      ],
      "modified": "2026-11-01T02:30:29.261758633Z",
      "provider": "osv",
      "references": [
        "https://git.kernel.org/stable/c/197476b126010bac1b3199833c6966cd6f54c2a9",
        "https://git.kernel.org/stable/c/3859960daeb9b7b39b9847b5b0113bc6081eb735",
        "https://git.kernel.org/stable/c/6ad4f75ef9f3372fce8cad494e789ac6a5507bef",
        "https://git.kernel.org/stable/c/8776032fe989a9b5fc77f2de5e03e4adb44c630e",
        "https://git.kernel.org/stable/c/a7511dcd9dd4bc55d123f9b800c8a4ed2662e5c6",
        "https://git.kernel.org/stable/c/ca5b0781946d5083ceafa752141f47f085853620",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/63xxx/CVE-2026-63949.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-63949",
        "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"
      ],
      "provider_metadata": {
        "cna_assigner": "Linux",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/63xxx/CVE-2026-63949.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-63949",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": null
  },
  "source_id": "core-osv",
  "document_id": 521316,
  "published_at": "2026-07-19T14:55:42.679+00:00"
}