CVE-2026-63949 (GCVE-0-2026-63949)

Vulnerability from cvelistv5 – Published: 2026-07-19 14:55 – Updated: 2026-07-19 14:55
VLAI
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-led-gpio.
Severity
No CVSS data available.
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 7e76aece6f036cb7ada4858d6aa73825bfe22983 , < ca5b0781946d5083ceafa752141f47f085853620 (git)
Affected: 7e76aece6f036cb7ada4858d6aa73825bfe22983 , < 8776032fe989a9b5fc77f2de5e03e4adb44c630e (git)
Affected: 7e76aece6f036cb7ada4858d6aa73825bfe22983 , < 3859960daeb9b7b39b9847b5b0113bc6081eb735 (git)
Affected: 7e76aece6f036cb7ada4858d6aa73825bfe22983 , < 197476b126010bac1b3199833c6966cd6f54c2a9 (git)
Affected: 7e76aece6f036cb7ada4858d6aa73825bfe22983 , < 6ad4f75ef9f3372fce8cad494e789ac6a5507bef (git)
Affected: 7e76aece6f036cb7ada4858d6aa73825bfe22983 , < a7511dcd9dd4bc55d123f9b800c8a4ed2662e5c6 (git)
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Linux Linux Affected: 5.16
Unaffected: 0 , < 5.16 (semver)
Unaffected: 6.1.176 , ≤ 6.1.* (semver)
Unaffected: 6.6.143 , ≤ 6.6.* (semver)
Unaffected: 6.12.93 , ≤ 6.12.* (semver)
Unaffected: 6.18.35 , ≤ 6.18.* (semver)
Unaffected: 7.0.12 , ≤ 7.0.* (semver)
Unaffected: 7.1 , ≤ * (original_commit_for_fix)
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          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nauxdisplay: line-display: fix OOB read on zero-length message_store()\n\nlinedisp_display() unconditionally reads msg[count - 1] before\nchecking whether count is zero, so a write of zero bytes to the\nmessage sysfs attribute hits msg[-1]:\n\n\twrite(fd, \"\", 0);\n\n\t-\u003e message_store(..., buf, count=0)\n\t   -\u003e linedisp_display(linedisp, buf, count=0)\n\t      -\u003e msg[count - 1] == \u0027\\n\u0027  ; OOB read\n\nThe kernfs write buffer for that store is a 1-byte allocation\n(kernfs_fop_write_iter() does kmalloc(len + 1) with len == 0),\nso msg[-1] is a 1-byte read before the slab object. On a\nKASAN-enabled kernel this trips an out-of-bounds report and\npanics; on stock kernels it silently reads adjacent slab data\nand, if that byte happens to be \u0027\\n\u0027, the following count--\nwraps ssize_t 0 to -1 and is then passed to kmemdup_nul().\n\nlinedisp_display() is reached from the message_store() sysfs\ncallback (drivers/auxdisplay/line-display.c message attribute,\nmode 0644) and from the in-tree initial-message setup with\ncount == -1, so the OOB path is only userspace-triggerable via\nzero-byte writes; vfs_write() does not short-circuit on\ncount == 0 and kernfs_fop_write_iter() dispatches the store\ncallback regardless.\n\nGuard the trailing-newline trim with a count check. The\nexisting if (!count) block then takes the clear-display path\nunchanged.\n\nAffects every auxdisplay driver that registers via\nlinedisp_register() / linedisp_attach(): ht16k33, max6959,\nimg-ascii-lcd, seg-led-gpio."
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    "dateUpdated": "2026-07-19T14:55:42.679Z",
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          }
        ],
        "id": "CVE-2026-63949",
        "lastModified": "2026-07-27T17:44:23.777",
        "metrics": {},
        "published": "2026-07-19T16:17:13.600",
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        "vulnStatus": "Awaiting Analysis"
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    "redhat_vex": {
      "aggregate_severity": "None",
      "current_release_date": "2026-07-21T11:08:11+00:00",
      "cve": "CVE-2026-63949",
      "id": "CVE-2026-63949",
      "initial_release_date": "2026-07-19T00:00:00+00:00",
      "product_status:known_not_affected": "274",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: auxdisplay: line-display: fix OOB read on zero-length message_store()",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-63949.json",
      "version": "3"
    },
    "suse_vex": {
      "aggregate_severity": "low",
      "current_release_date": "2026-09-18T00:45:57Z",
      "cve": "CVE-2026-63949",
      "id": "CVE-2026-63949",
      "initial_release_date": "2026-07-21T13:02:55Z",
      "product_status:first_fixed": "2",
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      "product_status:recommended": "250",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2026-63949",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2026-63949.json",
      "version": "9"
    }
  }
}



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