Answer in brief
CVE-2026-74635 records a Unknown severity vulnerability in fbdev: bitblit: bound-check glyph index in bit_cursor(). The current sources do not mark it as known exploited. The current feed maps Linux/Linux (generic), Linux/Linux (generic). Check affected ranges and fixed versions before updating.
Analysis pending evidence review
HOL Guard separates source facts from reviewed analysis. See the methodology.
A CVSS score is not reported in the current record. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.
Analysis status
Analysis pending evidence review
Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.
The current feed maps Linux/Linux (generic), Linux/Linux (generic). Check affected ranges and fixed versions before updating.
| Package | Affected range | Fixed version |
|---|---|---|
| Linux/Linuxgeneric | >=0998a6cb232674408a03e8561dc15aa266b2f53b <250159ace2dc53c1bdad267aa8da51b638748700 || >=db5c9a162d2f42bcc842b76b3d935dcc050a0eec <46336f476484f36145e5117e72d7b590f47433ee || >=c12003bf91fdff381c55ef54fef3e961a5af2545 <bf750cfeacf4e47ac72dadc7f05839696efb8576 || >=9ba1a7802ca9a2590cef95b253e6526f4364477f <94134d70abf9273b70499d97d0adc9185ef21091 || >=901f44227072be60812fe8083e83e1533c04eed1 <c1e7351767dd30fc574395c82121e4c67b882da3 || >=18c4ef4e765a798b47980555ed665d78b71aeadf <bc9db0d879c655d5dfd8add32fd60f13e65d132c || >=18c4ef4e765a798b47980555ed665d78b71aeadf <9ea879862e66e354e616028c31b39aa3eb6d35d8 || >=18c4ef4e765a798b47980555ed665d78b71aeadf <e033cbf3975a8465f879ebd5989dc35b04423a4d || a10cede006f9614b465cf25609a8753efbfd45cc || efaf89a75a29b2d179bf4fe63ca62852e93ad620 || >=5.10.247 <5.10.265 || >=5.15.197 <5.15.216 || >=6.1.159 <6.1.183 || >=6.6.117 <6.6.152 || >=6.12.58 <6.12.104 || >=5.4.302 <5.5 || >=6.17.8 <6.18 | 250159ace2dc53c1bdad267aa8da51b638748700, 46336f476484f36145e5117e72d7b590f47433ee, bf750cfeacf4e47ac72dadc7f05839696efb8576, 94134d70abf9273b70499d97d0adc9185ef21091, c1e7351767dd30fc574395c82121e4c67b882da3, bc9db0d879c655d5dfd8add32fd60f13e65d132c, 9ea879862e66e354e616028c31b39aa3eb6d35d8, e033cbf3975a8465f879ebd5989dc35b04423a4d, 5.10.265, 5.15.216, 6.1.183, 6.6.152, 6.12.104, 5.5, 6.18 |
| Linux/Linuxgeneric | 6.18 | Not reported |
Published upstream
Aug 22, 2026
Evidence: source:cvelist:source_dates:source-dates:recordSource modified
Aug 22, 2026
Evidence: source:cvelist:source_dates:source-dates:recordFirst seen by HOL
Aug 22, 2026
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.
Quoted source text, attributed separately from HOL analysis.