{"id":"CVE-2026-98838","title":"vt: skip screen update for DEC alignment test on backgroup consoles","summary":"In the Linux kernel, the following vulnerability has been resolved:\n\nvt: skip screen update for DEC alignment test on backgroup consoles\n\n[BUG]\nRecently, we encountered a KASAN warning as follows:\n\nBUG: KASAN: slab-out-of-bounds in fb_pa…","severity":"none","vendor":"Linux","product":"Linux","affected":["Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 985c000b046ca4ee11ee34ef85db500c569ef6e8","Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < ad06f7312d3f615dd466483ce81a9b9619166686","Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 0ee53081425a1a31ce15089012cd96b8353eb44e","Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 0928ed9bd7946baee911efa401088697836e3b1e","Linux 2.6.12"],"published":"2026-10-18","updated":"2026-10-18","sourceUpdated":"2026-10-18T15:50:07.004Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-98838","references":[{"url":"https://git.kernel.org/stable/c/985c000b046ca4ee11ee34ef85db500c569ef6e8"},{"url":"https://git.kernel.org/stable/c/ad06f7312d3f615dd466483ce81a9b9619166686"},{"url":"https://git.kernel.org/stable/c/0ee53081425a1a31ce15089012cd96b8353eb44e"},{"url":"https://git.kernel.org/stable/c/0928ed9bd7946baee911efa401088697836e3b1e"}],"tags":["cve.org"],"ingestedAt":"2026-10-18T16:47:32.468Z","slug":"CVE-2026-98838","body":"## Overview\n\nIn the Linux kernel, the following vulnerability has been resolved:\n\nvt: skip screen update for DEC alignment test on backgroup consoles\n\n[BUG]\nRecently, we encountered a KASAN warning as follows:\n\nBUG: KASAN: slab-out-of-bounds in fb_pad_aligned_buffer+0x11f/0x140\nRead of size 1 at addr ff1100015fd9f6a4 by task tty_fbcon_oob/1239\nCPU: 7 UID: 0 PID: 1239 Comm: tty_fbcon_oob Not tainted 7.3.0-rc1 #100 PREEMPT(full)\nHardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.17.0-4.fc41 04/01/2014\nCall Trace:\n <TASK>\n ...\n kasan_report+0xf0/0x120\n fb_pad_aligned_buffer+0x11f/0x140\n ccw_putcs+0x86c/0xa80\n fbcon_putcs+0x338/0x410\n do_update_region+0x21d/0x450\n do_con_write+0x1e0e/0x4880\n con_write+0x13/0x80\n n_tty_write+0x374/0x1010\n file_tty_write.isra.0+0x404/0x7a0\n ...\n\nreproduce:\n1) open /dev/tty0, set a KDFONTOP ioctl with op.op = KD_FONT_OP_SET,\nop.width = 8 and op.height = 16 (visible VC1)\n2) open /dev/tty1, set a KDFONTOP ioctl with op.op = KD_FONT_OP_SET,\nop.width = 28 and op.height = 24 (invisible VC2)\n3) echo 3 > /sys/devices/virtual/graphics/fbcon/rotate_all\n4) write EShash8(esc hash8) to tty1\n\n[CAUSE]\nAll VCs render to the framebuffer. setfont only modifies the target VC's\nfont without resizing the framebuffer backing buffer (par->rotated.buf);\nthe buffer is only resized for the visible VC\n(fbcon_do_set_font -> ... -> vc_do_resize -> update_screen). This relies on\nthe con_should_update() check performed before every update_region().\n\nHowever, the ESC # 8 path (do_con_trol -> do_update_region) omits the\ncon_should_update() check. After changing the font size of an invisible VC,\ndo_update_region() fills using the new font size against a buffer that was\nnever resized, causing an out-of-bounds access.\n\n[FIX]\nOnly push the update when the console is visible and not blanked, add\nthe con_should_update() check in the do_con_trol() like every other call\nsite of do_update_region() (update_region(), invert_screen(), ...).\n\n## Affected\n\n- `Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 985c000b046ca4ee11ee34ef85db500c569ef6e8`\n- `Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < ad06f7312d3f615dd466483ce81a9b9619166686`\n- `Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 0ee53081425a1a31ce15089012cd96b8353eb44e`\n- `Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 0928ed9bd7946baee911efa401088697836e3b1e`\n- `Linux 2.6.12`\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"sunlit","depthScore":3,"depthScoreParts":{"impact":2.8,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}