CVE-2026-74635
- Source
- https://cve.org/CVERecord?id=CVE-2026-74635
- Import Source
- https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-74635.json
- JSON Data
- https://api.osv.dev/v1/vulns/CVE-2026-74635
- Downstream
- Published
- 2026-08-22T15:32:15Z
- Modified
- 2026-10-08T02:51:54Z
- Severity
-
- 7.8 (High) CVSS_V3 - CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H CVSS Calculator
- Summary
- fbdev: bitblit: bound-check glyph index in bit_cursor()
- Details
-
In the Linux kernel, the following vulnerability has been resolved:
fbdev: bitblit: bound-check glyph index in bit_cursor()
bit_cursor() fetches the glyph under the cursor with
c = scr_readw(vc_pos); src = vc_font.data + ((c & charmask) * w * height);where charmask is 0x1ff when vc_hi_font_mask is set. The screen buffer value comes directly from scr_readw() and may be larger than the current font's glyph count.
Syzkaller triggers this via vcs_write(). The Call Trace shows vcs_write() in vc_screen.c writing an arbitrary 16-bit value with writev() to /dev/vcsa, which vcs_write_buf() in vc_screen.c stores via vcs_scr_writew() without checking charcount. The stored value is later read in bit_cursor() in bitblit.c.
When the font is changed from a font with 512 glyphs to a font with 256 glyphs, the screen buffer can retain characters with the high bit set from the previous mode, which could also produce the same out-of-bounds access.
BUG: KASAN: global-out-of-bounds in soft_cursor+0x378/0x6bc drivers/video/fbdev/core/softcursor.c:70 Read of size 16 at addr ffff800086c57970
Call Trace: soft_cursor+0x378/0x6bc drivers/video/fbdev/core/softcursor.c:70 bit_cursor+0xa90/0x1108 drivers/video/fbdev/core/bitblit.c:365 fbcon_cursor+0x344/0x498 drivers/video/fbdev/core/fbcon.c:1427 hide_cursor+0xdc/0x2d0 drivers/tty/vt/vt.c:883 update_region+0x100/0x18c drivers/tty/vt/vt.c:669 vcs_write+0x8ec/0xaf0 drivers/tty/vt/vc_screen.c:685
bit_putcs_aligned() and bit_putcs_unaligned() already clamp the glyph index to vc_font.charcount. Apply the same clamp in bit_cursor() after extracting the attribute and masking, before indexing fontdata.
The fix completes the bounds checking started in commit 18c4ef4e765a ("fbdev: bitblit: bound-check glyph index in bit_putcs*"), which missed the cursor path.
This change should be safe because the clamp reuses the existing contract from fbcon: charcount is maintained under console_lock in con_font_set() and fbcon_font_set(), and hi_font_mask is cleared when switching from 512 to 256 glyphs. When stale screen data with high bits remains after a font switch, or when vcs_write() stores an arbitrary value, clamping the index to 0 prevents the out-of-bounds read without changing cursor semantics — the same fallback bit_putcs uses.
- Database specific
{ "cna_assigner": "Linux", "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/74xxx/CVE-2026-74635.json" }- References
-
- https://git.kernel.org/stable/c/250159ace2dc53c1bdad267aa8da51b638748700
- https://git.kernel.org/stable/c/46336f476484f36145e5117e72d7b590f47433ee
- https://git.kernel.org/stable/c/94134d70abf9273b70499d97d0adc9185ef21091
- https://git.kernel.org/stable/c/9ea879862e66e354e616028c31b39aa3eb6d35d8
- https://git.kernel.org/stable/c/bc9db0d879c655d5dfd8add32fd60f13e65d132c
- https://git.kernel.org/stable/c/bf750cfeacf4e47ac72dadc7f05839696efb8576
- https://git.kernel.org/stable/c/c1e7351767dd30fc574395c82121e4c67b882da3
- https://git.kernel.org/stable/c/e033cbf3975a8465f879ebd5989dc35b04423a4d
- https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/74xxx/CVE-2026-74635.json
- https://nvd.nist.gov/vuln/detail/CVE-2026-74635
- https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
Affected packages
Git / git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
Affected ranges
- Type
- GIT
- Repo
- https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
- Events
-
Introduced0998a6cb232674408a03e8561dc15aa266b2f53bFixed250159ace2dc53c1bdad267aa8da51b638748700
- Type
- GIT
- Repo
- https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
- Events
-
Introduceddb5c9a162d2f42bcc842b76b3d935dcc050a0eecFixed46336f476484f36145e5117e72d7b590f47433ee
- Type
- GIT
- Repo
- https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
- Events
-
Introducedc12003bf91fdff381c55ef54fef3e961a5af2545Fixedbf750cfeacf4e47ac72dadc7f05839696efb8576
- Type
- GIT
- Repo
- https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
- Events
-
Introduced9ba1a7802ca9a2590cef95b253e6526f4364477fFixed94134d70abf9273b70499d97d0adc9185ef21091
- Type
- GIT
- Repo
- https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
- Events
-
Introduced901f44227072be60812fe8083e83e1533c04eed1Fixedc1e7351767dd30fc574395c82121e4c67b882da3
- Type
- GIT
- Repo
- https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
- Events
-
Introduced18c4ef4e765a798b47980555ed665d78b71aeadfFixedbc9db0d879c655d5dfd8add32fd60f13e65d132cFixed9ea879862e66e354e616028c31b39aa3eb6d35d8Fixede033cbf3975a8465f879ebd5989dc35b04423a4d
- Type
- GIT
- Repo
- https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
- Events
-
Introduced5.10.247Fixed5.10.265
- Type
- GIT
- Repo
- https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
- Events
-
Introduced5.15.197Fixed5.15.216
- Type
- GIT
- Repo
- https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
- Events
-
Introduced6.1.159Fixed6.1.183
- Type
- GIT
- Repo
- https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
- Events
-
Introduced6.6.117Fixed6.6.152
- Type
- GIT
- Repo
- https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
- Events
-
Introduced6.12.58Fixed6.12.104
- Type
- GIT
- Repo
- https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
- Events
-
Introduced5.4.302Fixed5.5
- Type
- GIT
- Repo
- https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
- Events
-
Introduced6.17.8Fixed6.18
- Type
- GIT
- Repo
- https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
- Events
-
Introduceda10cede006f9614b465cf25609a8753efbfd45cc
- Type
- GIT
- Repo
- https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
- Events
-
Introducedefaf89a75a29b2d179bf4fe63ca62852e93ad620
Affected versions
v5.*
v6.*
Linux / Kernel
Package
- Name
- Kernel
Affected ranges
- Type
- ECOSYSTEM
- Events
-
Introduced0 Unknown introduced version / All previous versions are affectedFixed5.10.265
- Type
- ECOSYSTEM
- Events
-
Introduced5.11.0Fixed5.15.216
- Type
- ECOSYSTEM
- Events
-
Introduced5.16.0Fixed6.1.183
- Type
- ECOSYSTEM
- Events
-
Introduced6.2.0Fixed6.6.152
- Type
- ECOSYSTEM
- Events
-
Introduced6.7.0Fixed6.12.104
- Type
- ECOSYSTEM
- Events
-
Introduced6.13.0Fixed6.18.45
- Type
- ECOSYSTEM
- Events
-
Introduced6.18.0Fixed7.1.9