Heimdall Security Logo

CVE-2026-74635

Vulnérabilité élevée dans Linux (Linux)

CVSS 7.8 · Élevée
EPSS 0.1%
Linux•Linux•Versions : <=6.1.*, <e033cbf3975a8465f879ebd5989dc35b04423a4d, <=6.12.*, 6.6.152, 18c4ef4e765a798b47980555ed665d78b71aeadf, 6.17.8, <5.10.265, <6.6.152, <94134d70abf9273b70499d97d0adc9185ef21091, <c1e7351767dd30fc574395c82121e4c67b882da3, 0, <5.15.216, <=7.1.*, <9ea879862e66e354e616028c31b39aa3eb6d35d8, 9ba1a7802ca9a2590cef95b253e6526f4364477f, 5.15.216, 6.18, db5c9a162d2f42bcc842b76b3d935dcc050a0eec, <46336f476484f36145e5117e72d7b590f47433ee, 5.10.247, <=5.10.*, <=6.6.*, 901f44227072be60812fe8083e83e1533c04eed1, efaf89a75a29b2d179bf4fe63ca62852e93ad620, 7.1.9, <250159ace2dc53c1bdad267aa8da51b638748700, <6.1.183, 5.4.302, 6.1.183, <5.5, <6.12.104, <=6.18.*, 6.12.104, 6.6.117, <bc9db0d879c655d5dfd8add32fd60f13e65d132c, a10cede006f9614b465cf25609a8753efbfd45cc, 5.15.197, 6.1.159, 6.12.58, <6.18, 6.18.45, <=*, <=5.15.*, 0998a6cb232674408a03e8561dc15aa266b2f53b, <bf750cfeacf4e47ac72dadc7f05839696efb8576, 5.10.265, 7.2, c12003bf91fdff381c55ef54fef3e961a5af2545

Description

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.

Gravité et risque d'exploitation

CVE-2026-74635 obtient un score CVSS de 7.8/10, soit une gravité élevée. Selon le modèle EPSS, la probabilité qu'elle soit exploitée dans les 30 prochains jours est de 0.13 %, ce qui la place devant 2.3 % des CVE référencées.

Que faire ?

  • Vérifiez si Linux (versions <=6.1.*, <e033cbf3975a8465f879ebd5989dc35b04423a4d, <=6.12.*, 6.6.152, 18c4ef4e765a798b47980555ed665d78b71aeadf, 6.17.8, <5.10.265, <6.6.152, <94134d70abf9273b70499d97d0adc9185ef21091, <c1e7351767dd30fc574395c82121e4c67b882da3, 0, <5.15.216, <=7.1.*, <9ea879862e66e354e616028c31b39aa3eb6d35d8, 9ba1a7802ca9a2590cef95b253e6526f4364477f, 5.15.216, 6.18, db5c9a162d2f42bcc842b76b3d935dcc050a0eec, <46336f476484f36145e5117e72d7b590f47433ee, 5.10.247, <=5.10.*, <=6.6.*, 901f44227072be60812fe8083e83e1533c04eed1, efaf89a75a29b2d179bf4fe63ca62852e93ad620, 7.1.9, <250159ace2dc53c1bdad267aa8da51b638748700, <6.1.183, 5.4.302, 6.1.183, <5.5, <6.12.104, <=6.18.*, 6.12.104, 6.6.117, <bc9db0d879c655d5dfd8add32fd60f13e65d132c, a10cede006f9614b465cf25609a8753efbfd45cc, 5.15.197, 6.1.159, 6.12.58, <6.18, 6.18.45, <=*, <=5.15.*, 0998a6cb232674408a03e8561dc15aa266b2f53b, <bf750cfeacf4e47ac72dadc7f05839696efb8576, 5.10.265, 7.2, c12003bf91fdff381c55ef54fef3e961a5af2545) est présent sur votre parc.
  • Appliquez le correctif ou la version corrigée indiqués dans les références de l'éditeur.
  • À défaut de correctif, limitez l'exposition (filtrage réseau, désactivation du composant).
  • Automatisez la détection : les agents CVE Heimdall (gratuits, open source) corrèlent l'inventaire de vos serveurs avec la base CVE.

Références

Rechercher une autre CVE