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vuln-cve/data/2025/39xxx/CVE-2025-39967.json
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{
"dataType": "CVE_RECORD",
"dataVersion": "5.2",
"cveMetadata": {
"cveId": "CVE-2025-39967",
"assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"state": "PUBLISHED",
"assignerShortName": "Linux",
"dateReserved": "2025-04-16T07:20:57.149Z",
"datePublished": "2025-10-15T07:55:51.554Z",
"dateUpdated": "2026-08-05T12:06:36.336Z"
},
"containers": {
"cna": {
"providerMetadata": {
"orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"shortName": "Linux",
"dateUpdated": "2026-08-05T12:06:36.336Z"
},
"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."
}
],
"metrics": [
{
"cvssV3_1": {
"version": "3.1",
"vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
"baseScore": 7.8,
"baseSeverity": "HIGH"
},
"scenarios": [
{
"lang": "en",
"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 — `width`, `height` and `charcount` come straight from the user-provided `struct console_font_op` — 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 — kernel pointers, credentials, other slab users' data — 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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"defaultStatus": "unaffected",
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
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],
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"programFiles": [
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],
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"versionType": "original_commit_for_fix"
}
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"cpeApplicability": [
{
"nodes": [
{
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"negate": false,
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"url": "https://git.kernel.org/stable/c/994bdc2d23c79087fbf7dcd9544454e8ebcef877"
},
{
"url": "https://git.kernel.org/stable/c/9c8ec14075c5317edd6b242f1be8167aa1e4e333"
},
{
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{
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],
"title": "fbcon: fix integer overflow in fbcon_do_set_font",
"x_generator": {
"engine": "bippy-1.2.0"
}
},
"adp": [
{
"metrics": [
{
"other": {
"type": "ssvc",
"content": {
"id": "CVE-2025-39967",
"role": "CISA Coordinator",
"options": [
{
"Exploitation": "none"
},
{
"Automatable": "no"
},
{
"Technical Impact": "total"
}
],
"version": "2.0.3",
"timestamp": "2026-06-10T20:42:14.769458Z"
}
}
}
],
"title": "CISA ADP Vulnrichment",
"providerMetadata": {
"orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
"shortName": "CISA-ADP",
"dateUpdated": "2026-06-11T18:44:20.970Z"
}
}
]
}
}
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