{ "dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": { "cveId": "CVE-2025-40323", "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "state": "PUBLISHED", "assignerShortName": "Linux", "dateReserved": "2025-04-16T07:20:57.186Z", "datePublished": "2025-12-08T00:46:50.833Z", "dateUpdated": "2026-08-05T12:09:36.199Z" }, "containers": { "cna": { "providerMetadata": { "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "shortName": "Linux", "dateUpdated": "2026-08-05T12:09:36.199Z" }, "descriptions": [ { "lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nfbcon: Set fb_display[i]->mode to NULL when the mode is released\n\nRecently, we discovered the following issue through syzkaller:\n\nBUG: KASAN: slab-use-after-free in fb_mode_is_equal+0x285/0x2f0\nRead of size 4 at addr ff11000001b3c69c by task syz.xxx\n...\nCall Trace:\n \n dump_stack_lvl+0xab/0xe0\n print_address_description.constprop.0+0x2c/0x390\n print_report+0xb9/0x280\n kasan_report+0xb8/0xf0\n fb_mode_is_equal+0x285/0x2f0\n fbcon_mode_deleted+0x129/0x180\n fb_set_var+0xe7f/0x11d0\n do_fb_ioctl+0x6a0/0x750\n fb_ioctl+0xe0/0x140\n __x64_sys_ioctl+0x193/0x210\n do_syscall_64+0x5f/0x9c0\n entry_SYSCALL_64_after_hwframe+0x76/0x7e\n\nBased on experimentation and analysis, during framebuffer unregistration,\nonly the memory of fb_info->modelist is freed, without setting the\ncorresponding fb_display[i]->mode to NULL for the freed modes. This leads\nto UAF issues during subsequent accesses. Here's an example of reproduction\nsteps:\n1. With /dev/fb0 already registered in the system, load a kernel module\n to register a new device /dev/fb1;\n2. Set fb1's mode to the global fb_display[] array (via FBIOPUT_CON2FBMAP);\n3. Switch console from fb to VGA (to allow normal rmmod of the ko);\n4. Unload the kernel module, at this point fb1's modelist is freed, leaving\n a wild pointer in fb_display[];\n5. Trigger the bug via system calls through fb0 attempting to delete a mode\n from fb0.\n\nAdd a check in do_unregister_framebuffer(): if the mode to be freed exists\nin fb_display[], set the corresponding mode pointer to NULL." } ], "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 vulnerability is reached through `ioctl()` on the `/dev/fbN` character device (`FBIOPUT_VSCREENINFO` / `FBIOPUT_CON2FBMAP`), which requires local access to the system. There is no remote or network-facing path into fbcon.\nAC:L - Once a framebuffer has been unregistered leaving a stale `fb_display[i].mode`, triggering the use-after-free is a single deterministic ioctl with no race to win and no memory-layout condition outside the attacker's control. The attacker can additionally groom the freed `fb_modelist` slab with controlled allocations before dereferencing it.\nPR:L - No capability check exists anywhere in the fbdev ioctl path — access is governed solely by DAC on `/dev/fbN`, which logged-in seat users obtain via logind `uaccess` ACLs or `video`/`graphics` group membership on desktops, kiosks, embedded devices and Android. An unprivileged local user with a console/seat can issue every ioctl involved.\nUI:N - The attacker performs all steps himself via ioctls on the framebuffer device; no victim action is needed. The framebuffer unregistration that creates the stale pointer occurs through ordinary system events such as USB display/dock removal or DRM driver unbind.\nS:U - The corruption and its consequences are confined to kernel memory within the same security authority; no VM, IOMMU, or sandbox boundary is crossed.\nC:H - The use-after-free reads a freed slab object that the attacker can reallocate with chosen or sensitive kernel data, and `display_to_var()`/`fb_videomode_to_var()` copy ~15 fields out of it into `info->var`, which is then readable from userspace via `FBIOGET_VSCREENINFO` — a repeatable kernel heap disclosure primitive.\nI:H - A use-after-free on a groomable kmalloc object permits heap spraying and type confusion with the reallocated victim object; the freed contents also propagate into `fb_check_var`/`fb_set_par` and console resize arithmetic, corrupting kernel state and enabling escalation to control-flow hijack.\nA:H - The reported syzkaller report is a KASAN slab-use-after-free that oopses the task in `fb_mode_is_equal()`; dereferencing the dangling pointer after the slab page is returned to the page allocator produces a kernel panic, and the stale pointer can be re-triggered repeatedly." } ] } ], "affected": [ { "product": "Linux", "vendor": "Linux", "defaultStatus": "unaffected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "drivers/video/fbdev/core/fbcon.c", "drivers/video/fbdev/core/fbmem.c", "include/linux/fbcon.h" ], "versions": [ { "version": "1da177e4c3f41524e886b7f1b8a0c1fc7321cac2", "lessThan": "39c2c1a2773aaf73e56906e5ef670114eb2d354f", "status": "affected", "versionType": "git" }, { "version": "1da177e4c3f41524e886b7f1b8a0c1fc7321cac2", "lessThan": "4ac18f0e6a6d599ca751c4cd98e522afc8e3d4eb", "status": "affected", "versionType": "git" }, { "version": "1da177e4c3f41524e886b7f1b8a0c1fc7321cac2", "lessThan": "468f78276a37f4c6499385a4ce28f4f57be6655d", "status": "affected", "versionType": "git" }, { "version": "1da177e4c3f41524e886b7f1b8a0c1fc7321cac2", "lessThan": "c079d42f70109512eee49123a843be91d8fa133f", "status": "affected", "versionType": "git" }, { "version": "1da177e4c3f41524e886b7f1b8a0c1fc7321cac2", "lessThan": "de89d19f4f30d9a8de87b9d08c1bd35cb70576d8", "status": "affected", "versionType": "git" }, { "version": "1da177e4c3f41524e886b7f1b8a0c1fc7321cac2", "lessThan": "a1f3058930745d2b938b6b4f5bd9630dc74b26b7", "status": "affected", "versionType": "git" } ] }, { "product": "Linux", "vendor": "Linux", "defaultStatus": "affected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "drivers/video/fbdev/core/fbcon.c", "drivers/video/fbdev/core/fbmem.c", "include/linux/fbcon.h" ], "versions": [ { "version": "2.6.12", "status": "affected" }, { "version": "0", "lessThan": "2.6.12", "status": "unaffected", "versionType": "semver" }, { "version": "5.15.203", "lessThanOrEqual": "5.15.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.1.159", "lessThanOrEqual": "6.1.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.6.117", "lessThanOrEqual": "6.6.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.12.58", "lessThanOrEqual": "6.12.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.17.8", "lessThanOrEqual": "6.17.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.18", "lessThanOrEqual": "*", "status": "unaffected", "versionType": "original_commit_for_fix" } ] } ], "cpeApplicability": [ { "nodes": [ { "operator": "OR", "negate": false, "cpeMatch": [ { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.12", "versionEndExcluding": "5.15.203" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.12", "versionEndExcluding": "6.1.159" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.12", "versionEndExcluding": "6.6.117" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.12", "versionEndExcluding": "6.12.58" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.12", "versionEndExcluding": "6.17.8" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.12", "versionEndExcluding": "6.18" } ] } ] } ], "references": [ { "url": "https://git.kernel.org/stable/c/39c2c1a2773aaf73e56906e5ef670114eb2d354f" }, { "url": "https://git.kernel.org/stable/c/4ac18f0e6a6d599ca751c4cd98e522afc8e3d4eb" }, { "url": "https://git.kernel.org/stable/c/468f78276a37f4c6499385a4ce28f4f57be6655d" }, { "url": "https://git.kernel.org/stable/c/c079d42f70109512eee49123a843be91d8fa133f" }, { "url": "https://git.kernel.org/stable/c/de89d19f4f30d9a8de87b9d08c1bd35cb70576d8" }, { "url": "https://git.kernel.org/stable/c/a1f3058930745d2b938b6b4f5bd9630dc74b26b7" } ], "title": "fbcon: Set fb_display[i]->mode to NULL when the mode is released", "x_generator": { "engine": "bippy-1.2.0" } } } }