{"api_version":"1","generated_at":"2026-08-22T21:56:29+00:00","cve":"CVE-2026-74635","urls":{"html":"https://cve.report/CVE-2026-74635","api":"https://cve.report/api/cve/CVE-2026-74635.json","docs":"https://cve.report/api","cve_org":"https://www.cve.org/CVERecord?id=CVE-2026-74635","nvd":"https://nvd.nist.gov/vuln/detail/CVE-2026-74635"},"summary":{"title":"fbdev: bitblit: bound-check glyph index in bit_cursor()","description":"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.","state":"PUBLISHED","assigner":"Linux","published_at":"2026-08-22 16:16:36","updated_at":"2026-08-22 16:16:36"},"problem_types":[],"metrics":[],"references":[{"url":"https://git.kernel.org/stable/c/46336f476484f36145e5117e72d7b590f47433ee","name":"https://git.kernel.org/stable/c/46336f476484f36145e5117e72d7b590f47433ee","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/9ea879862e66e354e616028c31b39aa3eb6d35d8","name":"https://git.kernel.org/stable/c/9ea879862e66e354e616028c31b39aa3eb6d35d8","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/c1e7351767dd30fc574395c82121e4c67b882da3","name":"https://git.kernel.org/stable/c/c1e7351767dd30fc574395c82121e4c67b882da3","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/e033cbf3975a8465f879ebd5989dc35b04423a4d","name":"https://git.kernel.org/stable/c/e033cbf3975a8465f879ebd5989dc35b04423a4d","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/bf750cfeacf4e47ac72dadc7f05839696efb8576","name":"https://git.kernel.org/stable/c/bf750cfeacf4e47ac72dadc7f05839696efb8576","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/94134d70abf9273b70499d97d0adc9185ef21091","name":"https://git.kernel.org/stable/c/94134d70abf9273b70499d97d0adc9185ef21091","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/250159ace2dc53c1bdad267aa8da51b638748700","name":"https://git.kernel.org/stable/c/250159ace2dc53c1bdad267aa8da51b638748700","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/bc9db0d879c655d5dfd8add32fd60f13e65d132c","name":"https://git.kernel.org/stable/c/bc9db0d879c655d5dfd8add32fd60f13e65d132c","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-74635","name":"CVE Program record","refsource":"CVE.ORG","tags":["canonical"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-74635","name":"NVD vulnerability detail","refsource":"NVD","tags":["canonical","analysis"]}],"affected":[{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 0998a6cb232674408a03e8561dc15aa266b2f53b 250159ace2dc53c1bdad267aa8da51b638748700 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected db5c9a162d2f42bcc842b76b3d935dcc050a0eec 46336f476484f36145e5117e72d7b590f47433ee git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected c12003bf91fdff381c55ef54fef3e961a5af2545 bf750cfeacf4e47ac72dadc7f05839696efb8576 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 9ba1a7802ca9a2590cef95b253e6526f4364477f 94134d70abf9273b70499d97d0adc9185ef21091 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 901f44227072be60812fe8083e83e1533c04eed1 c1e7351767dd30fc574395c82121e4c67b882da3 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 18c4ef4e765a798b47980555ed665d78b71aeadf bc9db0d879c655d5dfd8add32fd60f13e65d132c git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 18c4ef4e765a798b47980555ed665d78b71aeadf 9ea879862e66e354e616028c31b39aa3eb6d35d8 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 18c4ef4e765a798b47980555ed665d78b71aeadf e033cbf3975a8465f879ebd5989dc35b04423a4d git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected a10cede006f9614b465cf25609a8753efbfd45cc git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected efaf89a75a29b2d179bf4fe63ca62852e93ad620 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 5.10.247 5.10.265 semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 5.15.197 5.15.216 semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 6.1.159 6.1.183 semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 6.6.117 6.6.152 semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 6.12.58 6.12.104 semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 5.4.302 5.5 semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 6.17.8 6.18 semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 6.18","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 6.18 semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 5.10.265 5.10.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 5.15.216 5.15.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 6.1.183 6.1.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 6.6.152 6.6.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 6.12.104 6.12.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 6.18.45 6.18.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 7.1.9 7.1.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 7.2 * original_commit_for_fix","platforms":[]}],"timeline":[],"solutions":[],"workarounds":[],"exploits":[],"credits":[],"nvd_cpes":[],"vendor_comments":[],"enrichments":{"kev":null,"epss":null,"legacy_qids":[]},"source_records":{"cve_program":{"containers":{"cna":{"affected":[{"defaultStatus":"unaffected","product":"Linux","programFiles":["drivers/video/fbdev/core/bitblit.c"],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","vendor":"Linux","versions":[{"lessThan":"250159ace2dc53c1bdad267aa8da51b638748700","status":"affected","version":"0998a6cb232674408a03e8561dc15aa266b2f53b","versionType":"git"},{"lessThan":"46336f476484f36145e5117e72d7b590f47433ee","status":"affected","version":"db5c9a162d2f42bcc842b76b3d935dcc050a0eec","versionType":"git"},{"lessThan":"bf750cfeacf4e47ac72dadc7f05839696efb8576","status":"affected","version":"c12003bf91fdff381c55ef54fef3e961a5af2545","versionType":"git"},{"lessThan":"94134d70abf9273b70499d97d0adc9185ef21091","status":"affected","version":"9ba1a7802ca9a2590cef95b253e6526f4364477f","versionType":"git"},{"lessThan":"c1e7351767dd30fc574395c82121e4c67b882da3","status":"affected","version":"901f44227072be60812fe8083e83e1533c04eed1","versionType":"git"},{"lessThan":"bc9db0d879c655d5dfd8add32fd60f13e65d132c","status":"affected","version":"18c4ef4e765a798b47980555ed665d78b71aeadf","versionType":"git"},{"lessThan":"9ea879862e66e354e616028c31b39aa3eb6d35d8","status":"affected","version":"18c4ef4e765a798b47980555ed665d78b71aeadf","versionType":"git"},{"lessThan":"e033cbf3975a8465f879ebd5989dc35b04423a4d","status":"affected","version":"18c4ef4e765a798b47980555ed665d78b71aeadf","versionType":"git"},{"status":"affected","version":"a10cede006f9614b465cf25609a8753efbfd45cc","versionType":"git"},{"status":"affected","version":"efaf89a75a29b2d179bf4fe63ca62852e93ad620","versionType":"git"},{"lessThan":"5.10.265","status":"affected","version":"5.10.247","versionType":"semver"},{"lessThan":"5.15.216","status":"affected","version":"5.15.197","versionType":"semver"},{"lessThan":"6.1.183","status":"affected","version":"6.1.159","versionType":"semver"},{"lessThan":"6.6.152","status":"affected","version":"6.6.117","versionType":"semver"},{"lessThan":"6.12.104","status":"affected","version":"6.12.58","versionType":"semver"},{"lessThan":"5.5","status":"affected","version":"5.4.302","versionType":"semver"},{"lessThan":"6.18","status":"affected","version":"6.17.8","versionType":"semver"}]},{"defaultStatus":"affected","product":"Linux","programFiles":["drivers/video/fbdev/core/bitblit.c"],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","vendor":"Linux","versions":[{"status":"affected","version":"6.18"},{"lessThan":"6.18","status":"unaffected","version":"0","versionType":"semver"},{"lessThanOrEqual":"5.10.*","status":"unaffected","version":"5.10.265","versionType":"semver"},{"lessThanOrEqual":"5.15.*","status":"unaffected","version":"5.15.216","versionType":"semver"},{"lessThanOrEqual":"6.1.*","status":"unaffected","version":"6.1.183","versionType":"semver"},{"lessThanOrEqual":"6.6.*","status":"unaffected","version":"6.6.152","versionType":"semver"},{"lessThanOrEqual":"6.12.*","status":"unaffected","version":"6.12.104","versionType":"semver"},{"lessThanOrEqual":"6.18.*","status":"unaffected","version":"6.18.45","versionType":"semver"},{"lessThanOrEqual":"7.1.*","status":"unaffected","version":"7.1.9","versionType":"semver"},{"lessThanOrEqual":"*","status":"unaffected","version":"7.2","versionType":"original_commit_for_fix"}]}],"cpeApplicability":[{"nodes":[{"cpeMatch":[{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"5.10.265","versionStartIncluding":"5.10.247","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"5.15.216","versionStartIncluding":"5.15.197","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"6.1.183","versionStartIncluding":"6.1.159","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"6.6.152","versionStartIncluding":"6.6.117","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"6.12.104","versionStartIncluding":"6.12.58","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"6.18.45","versionStartIncluding":"6.18","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"7.1.9","versionStartIncluding":"6.18","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"7.2","versionStartIncluding":"6.18","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.4.302","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.17.8","vulnerable":true}],"negate":false,"operator":"OR"}]}],"descriptions":[{"lang":"en","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."}],"providerMetadata":{"dateUpdated":"2026-08-22T15:32:15.280Z","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","shortName":"Linux"},"references":[{"url":"https://git.kernel.org/stable/c/250159ace2dc53c1bdad267aa8da51b638748700"},{"url":"https://git.kernel.org/stable/c/46336f476484f36145e5117e72d7b590f47433ee"},{"url":"https://git.kernel.org/stable/c/bf750cfeacf4e47ac72dadc7f05839696efb8576"},{"url":"https://git.kernel.org/stable/c/94134d70abf9273b70499d97d0adc9185ef21091"},{"url":"https://git.kernel.org/stable/c/c1e7351767dd30fc574395c82121e4c67b882da3"},{"url":"https://git.kernel.org/stable/c/bc9db0d879c655d5dfd8add32fd60f13e65d132c"},{"url":"https://git.kernel.org/stable/c/9ea879862e66e354e616028c31b39aa3eb6d35d8"},{"url":"https://git.kernel.org/stable/c/e033cbf3975a8465f879ebd5989dc35b04423a4d"}],"title":"fbdev: bitblit: bound-check glyph index in bit_cursor()","x_generator":{"engine":"bippy-1.2.0"}}},"cveMetadata":{"assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","assignerShortName":"Linux","cveId":"CVE-2026-74635","datePublished":"2026-08-22T15:32:15.280Z","dateReserved":"2026-08-15T05:44:03.922Z","dateUpdated":"2026-08-22T15:32:15.280Z","state":"PUBLISHED"},"dataType":"CVE_RECORD","dataVersion":"5.2"},"nvd":{"publishedDate":"2026-08-22 16:16:36","lastModifiedDate":"2026-08-22 16:16:36","problem_types":[],"metrics":[],"configurations":[]},"legacy_mitre":{"record":{"CveYear":"2026","CveId":"74635","Ordinal":"1","Title":"fbdev: bitblit: bound-check glyph index in bit_cursor()","CVE":"CVE-2026-74635","Year":"2026"},"notes":[{"CveYear":"2026","CveId":"74635","Ordinal":"1","NoteData":"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.","Type":"Description","Title":"fbdev: bitblit: bound-check glyph index in bit_cursor()"}]}}}