CVE-2026-53402 (GCVE-0-2026-53402)
Vulnerability from cvelistv5
Published
2026-07-19 12:02
Modified
2026-08-17 04:50
Severity ?
7.1 (High) - CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H
Summary
In the Linux kernel, the following vulnerability has been resolved: fbdev: fbcon: fix out-of-bounds read in err_out of fbcon_do_set_font() When fbcon_do_set_font() fails (e.g., due to a memory allocation failure inside vc_resize() under heavy memory pressure), it jumps to the `err_out` label to roll back the console state. However, the current rollback logic forgets to restore the `hi_font` state, leading to a severe state machine corruption. Earlier in the function, `set_vc_hi_font()` might be called to change `vc->vc_hi_font_mask` and mutate the screen buffer. If `vc_resize()` subsequently fails, the `err_out` path restores `vc_font.charcount` but entirely skips rolling back the `vc_hi_font_mask` and the screen buffer. This mismatch leaves the terminal in a desynchronized state. Because `vc_hi_font_mask` remains set, the VT subsystem will still accept character indices greater than 255 from userspace and write them to the screen buffer. Subsequent rendering calls (e.g., `fbcon_putcs()`) will then use these inflated indices to access the reverted, 256-character font array, leading to a deterministic out-of-bounds read and potential kernel memory disclosure. Fix this by adding the missing rollback logic for the `hi_font` mask and screen buffer in the error path.
References
Impacted products
Vendor Product Version
Linux Linux Version: 868749a7456dc48e93887a8474194e2ee6d6c21f
Version: ebd6f886aa2447fcfcdce5450c9e1028e1d681bb
Version: a5a923038d70d2d4a86cb4e3f32625a5ee6e7e24
Version: a5a923038d70d2d4a86cb4e3f32625a5ee6e7e24
Version: a5a923038d70d2d4a86cb4e3f32625a5ee6e7e24
Version: a5a923038d70d2d4a86cb4e3f32625a5ee6e7e24
Version: a5a923038d70d2d4a86cb4e3f32625a5ee6e7e24
Version: a5a923038d70d2d4a86cb4e3f32625a5ee6e7e24
Version: f08ccb792d3eaf1dc62d8cbf6a30d6522329f660
Version: 5.10.249   ≤
Version: 5.15.64   ≤
Version: 5.19.6   ≤
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{
  "containers": {
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        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "drivers/video/fbdev/core/fbcon.c"
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          "product": "Linux",
          "programFiles": [
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          "vendor": "Linux",
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      "cpeApplicability": [
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              "negate": false,
              "operator": "OR"
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      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nfbdev: fbcon: fix out-of-bounds read in err_out of fbcon_do_set_font()\n\nWhen fbcon_do_set_font() fails (e.g., due to a memory allocation failure\ninside vc_resize() under heavy memory pressure), it jumps to the `err_out`\nlabel to roll back the console state. However, the current rollback logic\nforgets to restore the `hi_font` state, leading to a severe state machine\ncorruption.\n\nEarlier in the function, `set_vc_hi_font()` might be called to change\n`vc-\u003evc_hi_font_mask` and mutate the screen buffer. If `vc_resize()`\nsubsequently fails, the `err_out` path restores `vc_font.charcount`\nbut entirely skips rolling back the `vc_hi_font_mask` and the screen\nbuffer.\n\nThis mismatch leaves the terminal in a desynchronized state. Because\n`vc_hi_font_mask` remains set, the VT subsystem will still accept\ncharacter indices greater than 255 from userspace and write them to the\nscreen buffer. Subsequent rendering calls (e.g., `fbcon_putcs()`) will\nthen use these inflated indices to access the reverted, 256-character\nfont array, leading to a deterministic out-of-bounds read and potential\nkernel memory disclosure.\n\nFix this by adding the missing rollback logic for the `hi_font` mask\nand screen buffer in the error path."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 7.1,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:L - The vulnerability is reached only through the KDFONTOP ioctl on a framebuffer-console virtual terminal (/dev/ttyN), which is a local syscall path with no network or physical-access vector.\nAC:L - An attacker who controls a session on an fbcon-backed VT can reliably trigger the bug by issuing a font-change ioctl with different dimensions and a 256\u2194512 glyph transition, then inducing vc_resize() failure through self-controlled memory pressure; no race or victim-dependent timing is required.\nPR:L - KDFONTOP font-set operations require only that the caller owns the controlling TTY (current-\u003esignal-\u003etty == tty), which any unprivileged local user with a console or VT session has; CAP_SYS_TTY_CONFIG is not required on that path.\nUI:N - Exploitation requires only the attacker\u0027s own ioctl and memory-pressure actions on their TTY; no action by another user or administrator is needed.\nS:U - Impact is confined to kernel memory disclosure and potential kernel crash within the same kernel security authority; there is no VM escape, sandbox escape, or cross-security-boundary effect.\nC:H - The desynchronized hi_font_mask causes deterministic out-of-bounds reads from the kernel font glyph buffer during fbcon rendering (e.g., bit_cursor and rotated putcs paths), enabling disclosure of adjacent kernel memory.\nI:N - The flaw is an out-of-bounds read with console state desynchronization; it does not provide an arbitrary kernel write, code execution, or other data-modification primitive.\nA:H - Out-of-bounds reads from kernel font data can cause kernel page faults and oopses, consistent with the prior syzkaller-reported fbcon font/resize failure class that produced unhandled page faults."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-17T04:50:55.659Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/cb016bcb40c81e7b19c4ae6143babb366dae8e20"
        },
        {
          "url": "https://git.kernel.org/stable/c/ac562193c36696513ae196171892e9338475c4bc"
        },
        {
          "url": "https://git.kernel.org/stable/c/3618a4c5b2591cfa83efe74f5b18c2d02b35c3f5"
        },
        {
          "url": "https://git.kernel.org/stable/c/a7a526fbc847f07ad3a503c7382189be5ab68574"
        },
        {
          "url": "https://git.kernel.org/stable/c/b5bb2c696e140c399cb874def2feedf61dee27d6"
        },
        {
          "url": "https://git.kernel.org/stable/c/076b1aa65f77a49bce5a48a4a55a397cfcafa2b8"
        },
        {
          "url": "https://git.kernel.org/stable/c/39815715cbcfabb16fc8c5f4a23deeda20f5df62"
        },
        {
          "url": "https://git.kernel.org/stable/c/8fdc8c2057eea08d40ce2c8eed41ff9e451c65c2"
        }
      ],
      "title": "fbdev: fbcon: fix out-of-bounds read in err_out of fbcon_do_set_font()",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-53402",
    "datePublished": "2026-07-19T12:02:01.795Z",
    "dateReserved": "2026-06-09T07:44:35.403Z",
    "dateUpdated": "2026-08-17T04:50:55.659Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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