High

CVE-2026-74635 — fbdev: bitblit: bound-check glyph index in bit_cursor()

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.

Published Aug 22, 2026 · Updated Oct 14, 2026 · Sources: NIST National Vulnerability Database, CVE Program (cve.org) e CISA ADP, GitHub Security Advisories · CNA: Linux

Low

Who exploits it and how urgent it is

A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.

No exploitation signal in the sources consulted so far.

How the score was calculated

EPSS 0.1% (30-day exploitation probability)+0
Technical severity (high)+6

The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.

Exploitation

Not confirmed

Not in CISA KEV — an absence of record, not proof it is unexploited.

EPSS FIRST

0.13%

ahead of 2% of scored CVEs · Oct 14, 2026

Affects

Linux

CVSS base

7.8

High · 3 source(s)

Remediation

Fixes and mitigations documented by the sources — linked to the original advisory.

No fix documented by the sources we poll. That does not mean none exists: check the vendor advisory.

First 24 hours

Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.

Identify exposed assets running the affected vendor/product/version combinations (Linux Linux).
No fix documented in the sources: reduce exposure and monitor the vendor advisory.
Search available logs for exploit probes, errors and authentication anomalies.

Affected scope

Vendor, product and versions as the sources word them.

Vendor	Product	Versions	Status	Source
Linux	Linux	version efaf89a75a29b2d179bf4fe63ca62852e93ad620version 6.18≥ 6.17.8 and < 6.18≥ 5.4.302 and < 5.5≥ 6.12.58 and < 6.12.104≥ 6.6.117 and < 6.6.152≥ 6.1.159 and < 6.1.183≥ 5.15.197 and < 5.15.216 and 10 more ≥ 5.10.247 and < 5.10.265≥ 0998a6cb232674408a03e8561dc15aa266b2f53b and < 250159ace2dc53c1bdad267aa8da51b638748700version a10cede006f9614b465cf25609a8753efbfd45cc≥ 18c4ef4e765a798b47980555ed665d78b71aeadf and < e033cbf3975a8465f879ebd5989dc35b04423a4d≥ 18c4ef4e765a798b47980555ed665d78b71aeadf and < 9ea879862e66e354e616028c31b39aa3eb6d35d8≥ 18c4ef4e765a798b47980555ed665d78b71aeadf and < bc9db0d879c655d5dfd8add32fd60f13e65d132c≥ 901f44227072be60812fe8083e83e1533c04eed1 and < c1e7351767dd30fc574395c82121e4c67b882da3≥ 9ba1a7802ca9a2590cef95b253e6526f4364477f and < 94134d70abf9273b70499d97d0adc9185ef21091≥ c12003bf91fdff381c55ef54fef3e961a5af2545 and < bf750cfeacf4e47ac72dadc7f05839696efb8576≥ db5c9a162d2f42bcc842b76b3d935dcc050a0eec and < 46336f476484f36145e5117e72d7b590f47433ee	Vulnerable	CVE Program (cve.org) e CISA ADP

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

Attack vector

Local

Attack complexity

Low

Privileges required

Low

User interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

High

Availability

High

Every base score collected

Sources score independently and may disagree; each row says who scored it and under which version.

Score	Version	Severity	Expl.	Impact	Scored by
7.8	CVSS 3.1	High	1.8	5.9	416baaa9-dc9f-4396-8d5f-8c081fb06d67 via NIST National Vulnerability Database
7.8	CVSS 3.1	High	—	—	GitHub, Inc. via GitHub Security Advisories
7.8	CVSS 3.1	High	—	—	Linux via CVE Program (cve.org) e CISA ADP

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H (score shown at the top: 416baaa9-dc9f-4396-8d5f-8c081fb06d67)

EPSS over time FIRST

Oct 13, 2026 → Oct 14, 2026 · 2 reading(s) · max 0.13%

Detection

Read off the CVSS vector and the weakness class. Starting points, not tested rules.

Local/physical vector: focus on endpoint telemetry (EDR) from affected hosts.

endpoint telemetry (EDR)

Timeline

What happened to this CVE, newest first.

2026
Affected products added · linux/linux
Oct 14, 2026 · CVE Program (cve.org) e CISA ADP
Record published
Oct 14, 2026
CVSS changed · 7.8
Oct 14, 2026 · NIST National Vulnerability Database
Source status changed · → Received
Oct 14, 2026 · NIST National Vulnerability Database
Record created in this database
Oct 14, 2026 · NIST National Vulnerability Database
CVE published
Aug 22, 2026 · Linux

Source activity

Repeated readings are counted rather than listed.

1× References added · Oct 14, 2026 – Oct 14, 2026
1× Official description updated · Oct 14, 2026 – Oct 14, 2026

References

10 on the record

git.kernel.org/stable/c/c1e7351767dd30fc574395c82121e4c67b882da3
NIST National Vulnerability Database
git.kernel.org/stable/c/bc9db0d879c655d5dfd8add32fd60f13e65d132c
NIST National Vulnerability Database
git.kernel.org/stable/c/9ea879862e66e354e616028c31b39aa3eb6d35d8
NIST National Vulnerability Database
git.kernel.org/stable/c/e033cbf3975a8465f879ebd5989dc35b04423a4d
NIST National Vulnerability Database
git.kernel.org/stable/c/bf750cfeacf4e47ac72dadc7f05839696efb8576
NIST National Vulnerability Database
git.kernel.org/stable/c/46336f476484f36145e5117e72d7b590f47433ee
NIST National Vulnerability Database
github.com/advisories/GHSA-gcm2-cr9p-5jc7
GitHub Security Advisories
git.kernel.org/stable/c/250159ace2dc53c1bdad267aa8da51b638748700
NIST National Vulnerability Database
nvd.nist.gov/vuln/detail/CVE-2026-74635
GitHub Security Advisories
git.kernel.org/stable/c/94134d70abf9273b70499d97d0adc9185ef21091
NIST National Vulnerability Database

Elsewhere on this site

Linux
every CVE for this vendor

Related CVEs (same products)

Critical CVE-2026-99999 ipv4: validate checksum_start before completing checksum 8h
Unknown CVE-2026-98432 ipv4: free inet_opt and ireq_opt after an RCU grace period 8h
Unknown CVE-2026-98424 wifi: cfg80211: undo netns switch if renaming the wiphy fails 1d
Unknown CVE-2026-98425 wifi: mac80211: don't warn when an IBSS has no channel to scan 1d
Unknown CVE-2026-98426 wifi: mwifiex: fix IRQ leak using wrong index in MSI-X error path 1d
Unknown CVE-2026-98427 net/sched: codel: bound the dropping loop per dequeue call 1d

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

No fixed version, patch or mitigation documented.
No CISA SSVC assessment.
No CWE classification.
No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record

Text assembled only from the fields above — no additional claims.

What should defenders know first?

CVE-2026-74635 is "fbdev: bitblit: bound-check glyph index in bit_cursor()", rated High. It affects Linux (Linux); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 7.8 describes technical severity. EPSS 0.13% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.

Comments

Moderated technical discussion. Read the community guidelines.

No comments yet.