Use-After-Free in Linux kernel (CVE-2021-47338)
Summary
Vulnerability in Linux kernel (CVE-2021-47338). Successful exploitation can lead to full system takeover.
Original description
The description as published by the source.
In the Linux kernel, the following vulnerability has been resolved:
fbmem: Do not delete the mode that is still in use
The execution of fb_delete_videomode() is not based on the result of the
previous fbcon_mode_deleted(). As a result, the mode is directly deleted,
regardless of whether it is still in use, which may cause UAF.
==================================================================
BUG: KASAN: use-after-free in fb_mode_is_equal+0x36e/0x5e0
drivers/video/fbdev/core/modedb.c:924
Read of size 4 at addr ffff88807e0ddb1c by task syz-executor.0/18962
CPU: 2 PID: 18962 Comm: syz-executor.0 Not tainted 5.10.45-rc1+ #3
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS ...
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x137/0x1be lib/dump_stack.c:118
print_address_description+0x6c/0x640 mm/kasan/report.c:385
__kasan_report mm/kasan/report.c:545 [inline]
kasan_report+0x13d/0x1e0 mm/kasan/report.c:562
fb_mode_is_equal+0x36e/0x5e0 drivers/video/fbdev/core/modedb.c:924
fbcon_mode_deleted+0x16a/0x220 drivers/video/fbdev/core/fbcon.c:2746
fb_set_var+0x1e1/0xdb0 drivers/video/fbdev/core/fbmem.c:975
do_fb_ioctl+0x4d9/0x6e0 drivers/video/fbdev/core/fbmem.c:1108
vfs_ioctl fs/ioctl.c:48 [inline]
__do_sys_ioctl fs/ioctl.c:753 [inline]
__se_sys_ioctl+0xfb/0x170 fs/ioctl.c:739
do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
entry_SYSCALL_64_after_hwframe+0x44/0xa9
Freed by task 18960:
kasan_save_stack mm/kasan/common.c:48 [inline]
kas…
Source: NIST National Vulnerability Database NVD
Auto-generated summary
Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.
A vulnerability tracked as CVE-2021-47338 has been found in Linux kernel.
Successful exploitation can lead to full system takeover. CVSS score: 7.8/10.
What to do: apply the vendor's official patched release.
If unsure, ask your IT team or search "Linux kernel CVE-2021-47338" on the vendor's site.
CVE-2021-47338 (Linux kernel) — CWE-416 / CVSS v3 7.8
Attack vector: local / no user interaction
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.
Use-after-free (CWE-416) exists in Linux kernel.
Check the vendor advisory for the affected versions of Linux kernel.
Severity: High (CVSS 7.8/10). Successful exploitation can lead to full system takeover.
Update to the patched release per vendor advisory.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Audit SBOM/dependencies to find affected services.
Response actions
Concrete steps and command examples for SOC/SRE teams to execute in order
-
1Identify exposure identify
Audit SBOM/dependencies for affected components.資産台帳・SBOM・依存マニフェストで Linux kernel を使っているサービスとバージョンを洗い出す。
-
2Post-deployment verification verify
Confirm patched version is live in productionパッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。
Fix status by distribution
Fixed packages published by each distribution for this CVE
- Debian DEBIAN-CVE-2021-47338 linux Fixed in: 5.14.6-1
- Ubuntu UBUNTU-CVE-2021-47338 linux-hwe-edge
References
- patch git.kernel.org
- patch git.kernel.org
- patch git.kernel.org
- patch git.kernel.org
- patch git.kernel.org