CVE-2025-39967 (GCVE-0-2025-39967)
Vulnerability from cvelistv5
Published
2025-10-15 07:55
Modified
2026-08-05 12:06
Severity ?
7.8 (High) - CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Summary
In the Linux kernel, the following vulnerability has been resolved: fbcon: fix integer overflow in fbcon_do_set_font Fix integer overflow vulnerabilities in fbcon_do_set_font() where font size calculations could overflow when handling user-controlled font parameters. The vulnerabilities occur when: 1. CALC_FONTSZ(h, pitch, charcount) performs h * pith * charcount multiplication with user-controlled values that can overflow. 2. FONT_EXTRA_WORDS * sizeof(int) + size addition can also overflow 3. This results in smaller allocations than expected, leading to buffer overflows during font data copying. Add explicit overflow checking using check_mul_overflow() and check_add_overflow() kernel helpers to safety validate all size calculations before allocation.
References
Impacted products
Vendor Product Version
Linux Linux Version: 96e41fc29e8af5c5085fb8a79cab8d0d00bab86c
Version: 39b3cffb8cf3111738ea993e2757ab382253d86a
Version: 39b3cffb8cf3111738ea993e2757ab382253d86a
Version: 39b3cffb8cf3111738ea993e2757ab382253d86a
Version: 39b3cffb8cf3111738ea993e2757ab382253d86a
Version: 39b3cffb8cf3111738ea993e2757ab382253d86a
Version: 39b3cffb8cf3111738ea993e2757ab382253d86a
Version: 39b3cffb8cf3111738ea993e2757ab382253d86a
Version: ae021a904ac82d9fc81c25329d3c465c5a7d5686
Version: 451bffa366f2cc0e5314807cb847f31c0226efed
Version: 2c455e9c5865861f5ce09c5f596909495ed7657c
Version: 72f099805dbc907fbe8fa19bccdc31d3e2ee6e9e
Version: 34cf1aff169dc6dedad8d79da7bf1b4de2773dbc
Version: 5.4.62   ≤
Version: 4.4.235   ≤
Version: 4.9.235   ≤
Version: 4.14.196   ≤
Version: 4.19.143   ≤
Version: 5.8.6   ≤
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          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nfbcon: fix integer overflow in fbcon_do_set_font\n\nFix integer overflow vulnerabilities in fbcon_do_set_font() where font\nsize calculations could overflow when handling user-controlled font\nparameters.\n\nThe vulnerabilities occur when:\n1. CALC_FONTSZ(h, pitch, charcount) performs h * pith * charcount\n   multiplication with user-controlled values that can overflow.\n2. FONT_EXTRA_WORDS * sizeof(int) + size addition can also overflow\n3. This results in smaller allocations than expected, leading to buffer\n   overflows during font data copying.\n\nAdd explicit overflow checking using check_mul_overflow() and\ncheck_add_overflow() kernel helpers to safety validate all size\ncalculations before allocation."
        }
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              "value": "AV:L - The only route to `fbcon_set_font()` is the `KDFONTOP` ioctl on a virtual console device (`/dev/ttyN`, `/dev/tty`), reached through `vt_ioctl()`/`con_font_op()`; there is no network, packet, or remote-peer input into this code.\nAC:L - The attacker supplies every operand of the faulty arithmetic \u2014 `width`, `height` and `charcount` come straight from the user-provided `struct console_font_op` \u2014 and the allocation-then-copy sequence is a single deterministic ioctl with no race to win, no memory grooming and no state the attacker cannot set up.\nPR:L - `vt_ioctl()` grants `perm` to any process whose controlling terminal is the VT, so an ordinary unprivileged user logged in on a virtual console (physical console, embedded/automotive/kiosk fbcon system, or a serial/VT login) can issue `KD_FONT_OP_SET` without any capability; only the alternative `CAP_SYS_TTY_CONFIG` route needs real root.\nUI:N - The attacker performs the ioctl on its own console session; no administrator or second user has to open a file, mount anything, or take any action.\nS:U - The undersized allocation and the overflowing copy both occur in kernel heap memory within the same security authority the attacker is already attacking; no VM, IOMMU, or sandbox boundary is crossed.\nC:H - A short kmalloc chunk followed by a length-mismatched copy loop corrupts adjacent slab objects, and the font is subsequently readable back via `KD_FONT_OP_GET`/`con_font_get()`, so out-of-bounds heap contents \u2014 kernel pointers, credentials, other slab users\u0027 data \u2014 can be disclosed to userspace.\nI:H - The overflow is an out-of-bounds heap write whose length and byte content are entirely attacker-chosen (the glyph bitmap), which is the classic primitive for overwriting neighbouring slab objects such as function pointers or `struct cred`, giving arbitrary modification and potential control-flow hijack.\nA:H - Writing past the end of the font allocation corrupts the slab and reliably produces a kernel oops, SLUB freelist BUG, or panic; the ioctl can be repeated at will, so it is a repeatable full-system denial of service."
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        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
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          "url": "https://git.kernel.org/stable/c/994bdc2d23c79087fbf7dcd9544454e8ebcef877"
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        {
          "url": "https://git.kernel.org/stable/c/9c8ec14075c5317edd6b242f1be8167aa1e4e333"
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        {
          "url": "https://git.kernel.org/stable/c/a6eb9f423b3db000aaedf83367b8539f6b72dcfc"
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          "url": "https://git.kernel.org/stable/c/adac90bb1aaf45ca66f9db8ac100be16750ace78"
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          "url": "https://git.kernel.org/stable/c/1a194e6c8e1ee745e914b0b7f50fa86c89ed13fe"
        }
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      "title": "fbcon: fix integer overflow in fbcon_do_set_font",
      "x_generator": {
        "engine": "bippy-1.2.0"
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  "cveMetadata": {
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    "assignerShortName": "Linux",
    "cveId": "CVE-2025-39967",
    "datePublished": "2025-10-15T07:55:51.554Z",
    "dateReserved": "2025-04-16T07:20:57.149Z",
    "dateUpdated": "2026-08-05T12:06:36.336Z",
    "state": "PUBLISHED"
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no network, packet, or remote-peer input into this code.\\nAC:L - The attacker supplies every operand of the faulty arithmetic \\u2014 `width`, `height` and `charcount` come straight from the user-provided `struct console_font_op` \\u2014 and the allocation-then-copy sequence is a single deterministic ioctl with no race to win, no memory grooming and no state the attacker cannot set up.\\nPR:L - `vt_ioctl()` grants `perm` to any process whose controlling terminal is the VT, so an ordinary unprivileged user logged in on a virtual console (physical console, embedded/automotive/kiosk fbcon system, or a serial/VT login) can issue `KD_FONT_OP_SET` without any capability; only the alternative `CAP_SYS_TTY_CONFIG` route needs real root.\\nUI:N - The attacker performs the ioctl on its own console session; no administrator or second user has to open a file, mount anything, or take any action.\\nS:U - The undersized allocation and the overflowing copy both occur in kernel heap memory within the same security authority the attacker is already attacking; no VM, IOMMU, or sandbox boundary is crossed.\\nC:H - A short kmalloc chunk followed by a length-mismatched copy loop corrupts adjacent slab objects, and the font is subsequently readable back via `KD_FONT_OP_GET`/`con_font_get()`, so out-of-bounds heap contents \\u2014 kernel pointers, credentials, other slab users\u0027 data \\u2014 can be disclosed to userspace.\\nI:H - The overflow is an out-of-bounds heap write whose length and byte content are entirely attacker-chosen (the glyph bitmap), which is the classic primitive for overwriting neighbouring slab objects such as function pointers or `struct cred`, giving arbitrary modification and potential control-flow hijack.\\nA:H - Writing past the end of the font allocation corrupts the slab and reliably produces a kernel oops, SLUB freelist BUG, or panic; the ioctl can be repeated at will, so it is a repeatable full-system denial of service.\"}]}], \"affected\": [{\"repo\": 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\"version\": \"34cf1aff169dc6dedad8d79da7bf1b4de2773dbc\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"5.4.62\", \"lessThan\": \"5.4.300\", \"versionType\": \"semver\"}, {\"status\": \"affected\", \"version\": \"4.4.235\", \"lessThan\": \"4.5\", \"versionType\": \"semver\"}, {\"status\": \"affected\", \"version\": \"4.9.235\", \"lessThan\": \"4.10\", \"versionType\": \"semver\"}, {\"status\": \"affected\", \"version\": \"4.14.196\", \"lessThan\": \"4.15\", \"versionType\": \"semver\"}, {\"status\": \"affected\", \"version\": \"4.19.143\", \"lessThan\": \"4.20\", \"versionType\": \"semver\"}, {\"status\": \"affected\", \"version\": \"5.8.6\", \"lessThan\": \"5.9\", \"versionType\": \"semver\"}], \"programFiles\": [\"drivers/video/fbdev/core/fbcon.c\"], \"defaultStatus\": \"unaffected\"}, {\"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\", \"vendor\": \"Linux\", \"product\": \"Linux\", \"versions\": [{\"status\": \"affected\", \"version\": \"5.9\"}, {\"status\": \"unaffected\", \"version\": \"0\", \"lessThan\": \"5.9\", \"versionType\": \"semver\"}, {\"status\": \"unaffected\", \"version\": \"5.4.300\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"5.4.*\"}, {\"status\": \"unaffected\", \"version\": \"5.10.245\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"5.10.*\"}, {\"status\": \"unaffected\", \"version\": \"5.15.194\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"5.15.*\"}, {\"status\": \"unaffected\", \"version\": \"6.1.155\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"6.1.*\"}, {\"status\": \"unaffected\", \"version\": \"6.6.109\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"6.6.*\"}, {\"status\": \"unaffected\", \"version\": \"6.12.50\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"6.12.*\"}, {\"status\": \"unaffected\", \"version\": \"6.16.10\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"6.16.*\"}, {\"status\": \"unaffected\", \"version\": \"6.17\", \"versionType\": \"original_commit_for_fix\", \"lessThanOrEqual\": \"*\"}], \"programFiles\": [\"drivers/video/fbdev/core/fbcon.c\"], \"defaultStatus\": \"affected\"}], \"references\": [{\"url\": \"https://git.kernel.org/stable/c/994bdc2d23c79087fbf7dcd9544454e8ebcef877\"}, {\"url\": \"https://git.kernel.org/stable/c/9c8ec14075c5317edd6b242f1be8167aa1e4e333\"}, {\"url\": \"https://git.kernel.org/stable/c/b8a6e85328aeb9881531dbe89bcd2637a06c3c95\"}, {\"url\": \"https://git.kernel.org/stable/c/a6eb9f423b3db000aaedf83367b8539f6b72dcfc\"}, {\"url\": \"https://git.kernel.org/stable/c/adac90bb1aaf45ca66f9db8ac100be16750ace78\"}, {\"url\": \"https://git.kernel.org/stable/c/4a4bac869560f943edbe3c2b032062f6673b13d3\"}, {\"url\": \"https://git.kernel.org/stable/c/c0c01f9aa08c8e10e10e8c9ebb5be01a4eff6eb7\"}, {\"url\": \"https://git.kernel.org/stable/c/1a194e6c8e1ee745e914b0b7f50fa86c89ed13fe\"}], \"x_generator\": {\"engine\": \"bippy-1.2.0\"}, \"descriptions\": [{\"lang\": \"en\", \"value\": \"In the Linux kernel, the following vulnerability has been resolved:\\n\\nfbcon: fix integer overflow in fbcon_do_set_font\\n\\nFix integer overflow vulnerabilities in fbcon_do_set_font() where font\\nsize calculations could overflow when handling user-controlled font\\nparameters.\\n\\nThe vulnerabilities occur when:\\n1. CALC_FONTSZ(h, pitch, charcount) performs h * pith * charcount\\n   multiplication with user-controlled values that can overflow.\\n2. FONT_EXTRA_WORDS * sizeof(int) + size addition can also overflow\\n3. This results in smaller allocations than expected, leading to buffer\\n   overflows during font data copying.\\n\\nAdd explicit overflow checking using check_mul_overflow() and\\ncheck_add_overflow() kernel helpers to safety validate all size\\ncalculations before allocation.\"}], \"cpeApplicability\": [{\"nodes\": [{\"negate\": false, \"cpeMatch\": [{\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"5.4.300\", \"versionStartIncluding\": \"5.4.62\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"5.10.245\", \"versionStartIncluding\": \"5.9\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"5.15.194\", \"versionStartIncluding\": \"5.9\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"6.1.155\", \"versionStartIncluding\": \"5.9\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"6.6.109\", \"versionStartIncluding\": \"5.9\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"6.12.50\", \"versionStartIncluding\": \"5.9\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"6.16.10\", \"versionStartIncluding\": \"5.9\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"6.17\", \"versionStartIncluding\": \"5.9\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionStartIncluding\": \"4.4.235\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionStartIncluding\": \"4.9.235\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionStartIncluding\": \"4.14.196\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionStartIncluding\": \"4.19.143\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionStartIncluding\": \"5.8.6\"}], \"operator\": \"OR\"}]}], \"providerMetadata\": {\"orgId\": \"416baaa9-dc9f-4396-8d5f-8c081fb06d67\", \"shortName\": \"Linux\", \"dateUpdated\": \"2026-08-05T12:06:36.336Z\"}}}",
      "cveMetadata": "{\"cveId\": \"CVE-2025-39967\", \"state\": \"PUBLISHED\", \"dateUpdated\": \"2026-08-05T12:06:36.336Z\", \"dateReserved\": \"2025-04-16T07:20:57.149Z\", \"assignerOrgId\": \"416baaa9-dc9f-4396-8d5f-8c081fb06d67\", \"datePublished\": \"2025-10-15T07:55:51.554Z\", \"assignerShortName\": \"Linux\"}",
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}


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