{"id":"CVE-2021-47383","state":"PUBLISHED","title":"tty: Fix out-of-bound vmalloc access in imageblit","description":"In the Linux kernel, the following vulnerability has been resolved:\n\ntty: Fix out-of-bound vmalloc access in imageblit\n\nThis issue happens when a userspace program does an ioctl\nFBIOPUT_VSCREENINFO passing the fb_var_screeninfo struct\ncontaining only the fields xres, yres, and bits_per_pixel\nwith values.\n\nIf this struct is the same as the previous ioctl, the\nvc_resize() detects it and doesn't call the resize_screen(),\nleaving the fb_var_screeninfo incomplete. And this leads to\nthe updatescrollmode() calculates a wrong value to\nfbcon_display->vrows, which makes the real_y() return a\nwrong value of y, and that value, eventually, causes\nthe imageblit to access an out-of-bound address value.\n\nTo solve this issue I made the resize_screen() be called\neven if the screen does not need any resizing, so it will\n\"fix and fill\" the fb_var_screeninfo independently.","publishedAt":"2024-05-21T15:03:44.286Z","updatedAt":"2026-08-05T08:47:33.469Z","severity":{"score":7.8,"label":"High","version":"3.1","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","source":"Linux"},"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"1da177e4c3f41524e886b7f1b8a0c1fc7321cac2","status":"affected","lessThan":"7e71fcedfda6f7de18f850a6b36e78d78b04476f","versionType":"git"},{"version":"1da177e4c3f41524e886b7f1b8a0c1fc7321cac2","status":"affected","lessThan":"70aed03b1d5a5df974f456cdc8eedb213c94bb8b","versionType":"git"},{"version":"1da177e4c3f41524e886b7f1b8a0c1fc7321cac2","status":"affected","lessThan":"067c694d06040db6f0c65281bb358452ca6d85b9","versionType":"git"},{"version":"1da177e4c3f41524e886b7f1b8a0c1fc7321cac2","status":"affected","lessThan":"8a6a240f52e14356386030d8958ae8b1761d2325","versionType":"git"},{"version":"1da177e4c3f41524e886b7f1b8a0c1fc7321cac2","status":"affected","lessThan":"883f7897a25e3ce14a7f274ca4c73f49ac84002a","versionType":"git"},{"version":"1da177e4c3f41524e886b7f1b8a0c1fc7321cac2","status":"affected","lessThan":"d570c48dd37dbe8fc6875d4461d01a9554ae2560","versionType":"git"},{"version":"1da177e4c3f41524e886b7f1b8a0c1fc7321cac2","status":"affected","lessThan":"699d926585daa6ec44be556cdc1ab89e5d54557b","versionType":"git"},{"version":"1da177e4c3f41524e886b7f1b8a0c1fc7321cac2","status":"affected","lessThan":"3b0c406124719b625b1aba431659f5cdc24a982c","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["drivers/tty/vt/vt.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"2.6.12","status":"affected"},{"version":"0","status":"unaffected","lessThan":"2.6.12","versionType":"semver"},{"version":"4.4.286","status":"unaffected","lessThanOrEqual":"4.4.*","versionType":"semver"},{"version":"4.9.285","status":"unaffected","lessThanOrEqual":"4.9.*","versionType":"semver"},{"version":"4.14.249","status":"unaffected","lessThanOrEqual":"4.14.*","versionType":"semver"},{"version":"4.19.209","status":"unaffected","lessThanOrEqual":"4.19.*","versionType":"semver"},{"version":"5.4.151","status":"unaffected","lessThanOrEqual":"5.4.*","versionType":"semver"},{"version":"5.10.71","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.14.10","status":"unaffected","lessThanOrEqual":"5.14.*","versionType":"semver"},{"version":"5.15","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["drivers/tty/vt/vt.c"]}],"references":["https://git.kernel.org/stable/c/7e71fcedfda6f7de18f850a6b36e78d78b04476f","https://git.kernel.org/stable/c/70aed03b1d5a5df974f456cdc8eedb213c94bb8b","https://git.kernel.org/stable/c/067c694d06040db6f0c65281bb358452ca6d85b9","https://git.kernel.org/stable/c/8a6a240f52e14356386030d8958ae8b1761d2325","https://git.kernel.org/stable/c/883f7897a25e3ce14a7f274ca4c73f49ac84002a","https://git.kernel.org/stable/c/d570c48dd37dbe8fc6875d4461d01a9554ae2560","https://git.kernel.org/stable/c/699d926585daa6ec44be556cdc1ab89e5d54557b","https://git.kernel.org/stable/c/3b0c406124719b625b1aba431659f5cdc24a982c"],"weaknesses":[],"ingestedAt":"2026-10-29T19:49:19.404Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2021/47xxx/CVE-2021-47383.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2021-47383","state":"PUBLISHED","datePublished":"2024-05-21T15:03:44.286Z","dateUpdated":"2026-08-05T08:47:33.469Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2024-05-21T14:58:30.812Z"},"containers":{"cna":{"title":"tty: Fix out-of-bound vmalloc access in imageblit","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\ntty: Fix out-of-bound vmalloc access in imageblit\n\nThis issue happens when a userspace program does an ioctl\nFBIOPUT_VSCREENINFO passing the fb_var_screeninfo struct\ncontaining only the fields xres, yres, and bits_per_pixel\nwith values.\n\nIf this struct is the same as the previous ioctl, the\nvc_resize() detects it and doesn't call the resize_screen(),\nleaving the fb_var_screeninfo incomplete. And this leads to\nthe updatescrollmode() calculates a wrong value to\nfbcon_display->vrows, which makes the real_y() return a\nwrong value of y, and that value, eventually, causes\nthe imageblit to access an out-of-bound address value.\n\nTo solve this issue I made the resize_screen() be called\neven if the screen does not need any resizing, so it will\n\"fix and fill\" the fb_var_screeninfo independently."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"1da177e4c3f41524e886b7f1b8a0c1fc7321cac2","status":"affected","lessThan":"7e71fcedfda6f7de18f850a6b36e78d78b04476f","versionType":"git"},{"version":"1da177e4c3f41524e886b7f1b8a0c1fc7321cac2","status":"affected","lessThan":"70aed03b1d5a5df974f456cdc8eedb213c94bb8b","versionType":"git"},{"version":"1da177e4c3f41524e886b7f1b8a0c1fc7321cac2","status":"affected","lessThan":"067c694d06040db6f0c65281bb358452ca6d85b9","versionType":"git"},{"version":"1da177e4c3f41524e886b7f1b8a0c1fc7321cac2","status":"affected","lessThan":"8a6a240f52e14356386030d8958ae8b1761d2325","versionType":"git"},{"version":"1da177e4c3f41524e886b7f1b8a0c1fc7321cac2","status":"affected","lessThan":"883f7897a25e3ce14a7f274ca4c73f49ac84002a","versionType":"git"},{"version":"1da177e4c3f41524e886b7f1b8a0c1fc7321cac2","status":"affected","lessThan":"d570c48dd37dbe8fc6875d4461d01a9554ae2560","versionType":"git"},{"version":"1da177e4c3f41524e886b7f1b8a0c1fc7321cac2","status":"affected","lessThan":"699d926585daa6ec44be556cdc1ab89e5d54557b","versionType":"git"},{"version":"1da177e4c3f41524e886b7f1b8a0c1fc7321cac2","status":"affected","lessThan":"3b0c406124719b625b1aba431659f5cdc24a982c","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["drivers/tty/vt/vt.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"2.6.12","status":"affected"},{"version":"0","status":"unaffected","lessThan":"2.6.12","versionType":"semver"},{"version":"4.4.286","status":"unaffected","lessThanOrEqual":"4.4.*","versionType":"semver"},{"version":"4.9.285","status":"unaffected","lessThanOrEqual":"4.9.*","versionType":"semver"},{"version":"4.14.249","status":"unaffected","lessThanOrEqual":"4.14.*","versionType":"semver"},{"version":"4.19.209","status":"unaffected","lessThanOrEqual":"4.19.*","versionType":"semver"},{"version":"5.4.151","status":"unaffected","lessThanOrEqual":"5.4.*","versionType":"semver"},{"version":"5.10.71","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.14.10","status":"unaffected","lessThanOrEqual":"5.14.*","versionType":"semver"},{"version":"5.15","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["drivers/tty/vt/vt.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/7e71fcedfda6f7de18f850a6b36e78d78b04476f"},{"url":"https://git.kernel.org/stable/c/70aed03b1d5a5df974f456cdc8eedb213c94bb8b"},{"url":"https://git.kernel.org/stable/c/067c694d06040db6f0c65281bb358452ca6d85b9"},{"url":"https://git.kernel.org/stable/c/8a6a240f52e14356386030d8958ae8b1761d2325"},{"url":"https://git.kernel.org/stable/c/883f7897a25e3ce14a7f274ca4c73f49ac84002a"},{"url":"https://git.kernel.org/stable/c/d570c48dd37dbe8fc6875d4461d01a9554ae2560"},{"url":"https://git.kernel.org/stable/c/699d926585daa6ec44be556cdc1ab89e5d54557b"},{"url":"https://git.kernel.org/stable/c/3b0c406124719b625b1aba431659f5cdc24a982c"}],"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 bug is triggered by a local FBIOPUT_VSCREENINFO ioctl on /dev/fbN that flows through fb_set_var → fbcon_modechanged → vc_do_resize → updatescrollmode → imageblit; it is not reachable via network or adjacent protocols.\nAC:L - A crafted incomplete fb_var_screeninfo (undersized/zero virtual resolution) deterministically drives negative fbcon_display->vrows and an OOB imageblit write; syzkaller has a reliable C repro with no race or attacker-independent conditions.\nPR:L - do_fb_ioctl/FBIOPUT_VSCREENINFO performs no capability check; access only requires opening /dev/fbN, which seated users, video-group members, and embedded/Android graphics processes commonly have without real root in the init namespace.\nUI:N - The attacker opens the framebuffer device and issues the ioctl directly; fbcon_modechanged calls update_screen on the same path, so no separate victim action is required.\nS:U - Impact is kernel memory corruption and crash within the same host security authority; it does not cross a VM, IOMMU, or other distinct boundary.\nC:H - The defect is kernel memory corruption via a vmalloc out-of-bounds access in imageblit; per guidance, such corruption can be leveraged for information disclosure and is scored High when uncertain.\nI:H - Syzbot confirms a KASAN vmalloc-out-of-bounds Write in fast_imageblit/sys_imageblit past screen_base; 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