360 lines
20 KiB
JSON
360 lines
20 KiB
JSON
{
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"dataType": "CVE_RECORD",
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"dataVersion": "5.2",
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"cveMetadata": {
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"cveId": "CVE-2026-74635",
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"assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
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"state": "PUBLISHED",
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"assignerShortName": "Linux",
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"dateReserved": "2026-08-15T05:44:03.922Z",
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"datePublished": "2026-08-22T15:32:15.280Z",
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"dateUpdated": "2026-10-16T19:06:04.057Z"
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},
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"containers": {
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"cna": {
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"providerMetadata": {
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"orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
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"shortName": "Linux",
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"dateUpdated": "2026-08-25T05:40:59.420Z"
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},
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"descriptions": [
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{
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"lang": "en",
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"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nfbdev: bitblit: bound-check glyph index in bit_cursor()\n\nbit_cursor() fetches the glyph under the cursor with\n\n\tc = scr_readw(vc_pos);\n\tsrc = vc_font.data + ((c & charmask) * w * height);\n\nwhere charmask is 0x1ff when vc_hi_font_mask is set. The screen buffer\nvalue comes directly from scr_readw() and may be larger than the current\nfont's glyph count.\n\nSyzkaller triggers this via vcs_write(). The Call Trace shows\nvcs_write() in vc_screen.c writing an arbitrary 16-bit value with\nwritev() to /dev/vcsa, which vcs_write_buf() in vc_screen.c stores via\nvcs_scr_writew() without checking charcount. The stored value is later\nread in bit_cursor() in bitblit.c.\n\nWhen the font is changed from a font with 512 glyphs to a font with\n256 glyphs, the screen buffer can retain characters with the high\nbit set from the previous mode, which could also produce the same\nout-of-bounds access.\n\n BUG: KASAN: global-out-of-bounds in soft_cursor+0x378/0x6bc drivers/video/fbdev/core/softcursor.c:70\n Read of size 16 at addr ffff800086c57970\n\n Call Trace:\n soft_cursor+0x378/0x6bc drivers/video/fbdev/core/softcursor.c:70\n bit_cursor+0xa90/0x1108 drivers/video/fbdev/core/bitblit.c:365\n fbcon_cursor+0x344/0x498 drivers/video/fbdev/core/fbcon.c:1427\n hide_cursor+0xdc/0x2d0 drivers/tty/vt/vt.c:883\n update_region+0x100/0x18c drivers/tty/vt/vt.c:669\n vcs_write+0x8ec/0xaf0 drivers/tty/vt/vc_screen.c:685\n\nbit_putcs_aligned() and bit_putcs_unaligned() already clamp the glyph\nindex to vc_font.charcount. Apply the same clamp in bit_cursor() after\nextracting the attribute and masking, before indexing fontdata.\n\nThe fix completes the bounds checking started in commit 18c4ef4e765a\n(\"fbdev: bitblit: bound-check glyph index in bit_putcs*\"), which missed\nthe cursor path.\n\nThis change should be safe because the clamp reuses the existing\ncontract from fbcon: charcount is maintained under console_lock in\ncon_font_set() and fbcon_font_set(), and hi_font_mask is cleared when\nswitching from 512 to 256 glyphs. When stale screen data with high bits\nremains after a font switch, or when vcs_write() stores an arbitrary\nvalue, clamping the index to 0 prevents the out-of-bounds read without\nchanging cursor semantics — the same fallback bit_putcs uses."
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}
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],
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"metrics": [
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{
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"cvssV3_1": {
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"version": "3.1",
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"vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
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"baseScore": 7.8,
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"baseSeverity": "HIGH"
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},
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"scenarios": [
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{
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"lang": "en",
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"value": "AV:L - Exploitation requires local write() to /dev/vcsa (or ioctl on an owned virtual console) to poison the VT screen buffer; the bug is in fbcon cursor rendering, not in any network-facing protocol handler.\nAC:L - Syzkaller reproduces the fault reliably by writing arbitrary screen-buffer values to /dev/vcsa; the attacker fully controls the glyph index and can repeat the trigger on every console refresh without races or victim-specific timing.\nPR:L - Triggering needs only a local account with write access to /dev/vcsa* (typically membership in the tty group) or a session owning the target console for KDFONTOP/font-switch paths; no CAP_SYS_ADMIN or init-namespace root is required.\nUI:N - Once the attacker has the needed local device access, exploitation is fully self-contained and does not require any additional action from another user or administrator.\nS:U - Impact is confined to kernel framebuffer-console memory within the same kernel security domain; it does not cross VM, container, or IOMMU boundaries to affect a separate authority.\nC:H - An out-of-bounds read past the font glyph table copies adjacent kernel memory (global or heap font data) into cursor buffers and framebuffer blit paths, disclosing more than a few bytes per trigger.\nI:H - The out-of-bounds glyph pointer feeds update_attr() and soft_cursor() memcpy paths that copy attacker-influenced kernel memory into kmalloc cursor buffers and framebuffer state, constituting kernel memory corruption with integrity impact.\nA:H - KASAN reports a kernel BUG on the out-of-bounds read in soft_cursor(), and repeated malicious /dev/vcsa writes force console refresh through hide_cursor(), enabling kernel oops/panic and console denial of service."
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}
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]
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}
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],
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"affected": [
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{
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"product": "Linux",
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"vendor": "Linux",
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"defaultStatus": "unaffected",
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"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
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"programFiles": [
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"drivers/video/fbdev/core/bitblit.c"
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],
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"versions": [
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{
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"version": "0998a6cb232674408a03e8561dc15aa266b2f53b",
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"lessThan": "250159ace2dc53c1bdad267aa8da51b638748700",
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"status": "affected",
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},
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"status": "affected",
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"versionType": "git"
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},
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"status": "affected",
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"versionType": "git"
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},
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"lessThan": "94134d70abf9273b70499d97d0adc9185ef21091",
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"status": "affected",
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"versionType": "git"
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},
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{
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"version": "901f44227072be60812fe8083e83e1533c04eed1",
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"lessThan": "c1e7351767dd30fc574395c82121e4c67b882da3",
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"status": "affected",
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"versionType": "git"
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},
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{
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"version": "18c4ef4e765a798b47980555ed665d78b71aeadf",
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"lessThan": "bc9db0d879c655d5dfd8add32fd60f13e65d132c",
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"status": "affected",
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"status": "affected",
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{
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"version": "a10cede006f9614b465cf25609a8753efbfd45cc",
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"status": "affected",
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},
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{
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"version": "efaf89a75a29b2d179bf4fe63ca62852e93ad620",
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"status": "affected",
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},
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{
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"version": "5.10.247",
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"lessThan": "5.10.265",
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"status": "affected",
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"versionType": "semver"
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},
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{
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"version": "5.15.197",
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"lessThan": "5.15.216",
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"status": "affected",
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},
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{
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"version": "6.1.159",
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"lessThan": "6.1.183",
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"status": "affected",
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},
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{
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"version": "6.6.117",
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"lessThan": "6.6.152",
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"status": "affected",
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},
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{
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"version": "6.12.58",
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"lessThan": "6.12.104",
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"status": "affected",
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},
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{
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"version": "5.4.302",
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"lessThan": "5.5",
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"status": "affected",
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{
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}
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{
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"product": "Linux",
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"vendor": "Linux",
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"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
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"drivers/video/fbdev/core/bitblit.c"
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],
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"status": "unaffected",
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},
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"version": "6.18.45",
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"lessThanOrEqual": "6.18.*",
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"status": "unaffected",
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},
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{
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"version": "7.1.9",
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"lessThanOrEqual": "7.1.*",
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"status": "unaffected",
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"versionType": "semver"
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},
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{
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"version": "7.2",
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"lessThanOrEqual": "*",
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"status": "unaffected",
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"versionType": "original_commit_for_fix"
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}
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]
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}
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],
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"cpeApplicability": [
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"nodes": [
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{
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"operator": "OR",
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"references": [
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{
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"url": "https://git.kernel.org/stable/c/250159ace2dc53c1bdad267aa8da51b638748700"
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},
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{
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"url": "https://git.kernel.org/stable/c/46336f476484f36145e5117e72d7b590f47433ee"
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},
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{
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"url": "https://git.kernel.org/stable/c/bf750cfeacf4e47ac72dadc7f05839696efb8576"
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},
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{
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"url": "https://git.kernel.org/stable/c/94134d70abf9273b70499d97d0adc9185ef21091"
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},
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{
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"url": "https://git.kernel.org/stable/c/c1e7351767dd30fc574395c82121e4c67b882da3"
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},
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{
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"url": "https://git.kernel.org/stable/c/bc9db0d879c655d5dfd8add32fd60f13e65d132c"
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},
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{
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"url": "https://git.kernel.org/stable/c/9ea879862e66e354e616028c31b39aa3eb6d35d8"
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},
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{
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"url": "https://git.kernel.org/stable/c/e033cbf3975a8465f879ebd5989dc35b04423a4d"
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}
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],
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"title": "fbdev: bitblit: bound-check glyph index in bit_cursor()",
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"x_generator": {
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"engine": "bippy-1.2.0"
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}
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},
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"adp": [
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{
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"metrics": [
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{
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"other": {
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"type": "ssvc",
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"content": {
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"id": "CVE-2026-74635",
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"role": "CISA Coordinator",
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"options": [
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{
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"Exploitation": "none"
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},
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{
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"Automatable": "no"
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},
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{
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"Technical Impact": "total"
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}
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],
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"version": "2.0.3",
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"timestamp": "2026-10-16T19:03:10.782063Z"
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}
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}
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}
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],
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"title": "CISA ADP Vulnrichment",
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"providerMetadata": {
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"orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
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"shortName": "CISA-ADP",
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"dateUpdated": "2026-10-16T19:06:04.057Z"
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}
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}
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]
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}
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} |