Use-After-Free in Linux kernel (CVE-2021-47656)
Summary
Vulnerability in Linux kernel (CVE-2021-47656). 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:
jffs2: fix use-after-free in jffs2_clear_xattr_subsystem
When we mount a jffs2 image, assume that the first few blocks of
the image are normal and contain at least one xattr-related inode,
but the next block is abnormal. As a result, an error is returned
in jffs2_scan_eraseblock(). jffs2_clear_xattr_subsystem() is then
called in jffs2_build_filesystem() and then again in
jffs2_do_fill_super().
Finally we can observe the following report:
BUG: KASAN: use-after-free in jffs2_clear_xattr_subsystem+0x95/0x6ac
Read of size 8 at addr ffff8881243384e0 by task mount/719
Call Trace:
dump_stack+0x115/0x16b
jffs2_clear_xattr_subsystem+0x95/0x6ac
jffs2_do_fill_super+0x84f/0xc30
jffs2_fill_super+0x2ea/0x4c0
mtd_get_sb+0x254/0x400
mtd_get_sb_by_nr+0x4f/0xd0
get_tree_mtd+0x498/0x840
jffs2_get_tree+0x25/0x30
vfs_get_tree+0x8d/0x2e0
path_mount+0x50f/0x1e50
do_mount+0x107/0x130
__se_sys_mount+0x1c5/0x2f0
__x64_sys_mount+0xc7/0x160
do_syscall_64+0x45/0x70
entry_SYSCALL_64_after_hwframe+0x44/0xa9
Allocated by task 719:
kasan_save_stack+0x23/0x60
__kasan_kmalloc.constprop.0+0x10b/0x120
kasan_slab_alloc+0x12/0x20
kmem_cache_alloc+0x1c0/0x870
jffs2_alloc_xattr_ref+0x2f/0xa0
jffs2_scan_medium.cold+0x3713/0x4794
jffs2_do_mount_fs.cold+0xa7/0x2253
jffs2_do_fill_super+0x383/0xc30
jffs2_fill_super+0x2ea/0x4c0
[..…
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-2021-47656 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-2021-47656" on the vendor's site.
CVE-2021-47656 (Linux kernel) — CWE-416 / CVSS v3 7.8
Attack vector: local / unauthenticated
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-2021-47656 linux Fixed in: 5.17.3-1
- Ubuntu UBUNTU-CVE-2021-47656 linux-azure Fixed in: 4.15.0-1146.161~14.04.1
References
- patch git.kernel.org
- patch git.kernel.org
- patch git.kernel.org
- patch git.kernel.org
- patch git.kernel.org
- patch git.kernel.org
- patch git.kernel.org
- patch git.kernel.org
- patch git.kernel.org