Use-After-Free in Linux kernel (CVE-2021-47402)
Summary
Vulnerability in Linux kernel (CVE-2021-47402). 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:
net: sched: flower: protect fl_walk() with rcu
Patch that refactored fl_walk() to use idr_for_each_entry_continue_ul()
also removed rcu protection of individual filters which causes following
use-after-free when filter is deleted concurrently. Fix fl_walk() to obtain
rcu read lock while iterating and taking the filter reference and temporary
release the lock while calling arg->fn() callback that can sleep.
KASAN trace:
[ 352.773640] ==================================================================
[ 352.775041] BUG: KASAN: use-after-free in fl_walk+0x159/0x240 [cls_flower]
[ 352.776304] Read of size 4 at addr ffff8881c8251480 by task tc/2987
[ 352.777862] CPU: 3 PID: 2987 Comm: tc Not tainted 5.15.0-rc2+ #2
[ 352.778980] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.13.0-0-gf21b5a4aeb02-prebuilt.qemu.org 04/01/2014
[ 352.781022] Call Trace:
[ 352.781573] dump_stack_lvl+0x46/0x5a
[ 352.782332] print_address_description.constprop.0+0x1f/0x140
[ 352.783400] ? fl_walk+0x159/0x240 [cls_flower]
[ 352.784292] ? fl_walk+0x159/0x240 [cls_flower]
[ 352.785138] kasan_report.cold+0x83/0xdf
[ 352.785851] ? fl_walk+0x159/0x240 [cls_flower]
[ 352.786587] kasan_check_range+0x145/0x1a0
[ 352.787337] fl_walk+0x159/0x240 [cls_flower]
[ 352.788163] ? fl_put+0x10/0x10 [cls_flower]
[ 352.789007] ? __mutex_unlock_slowpath.constprop.0+0x220/0x220
[ 352.790102] tcf_chain_dump+0x231/0…
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-2021-47402 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-2021-47402" on the vendor's site.
CVE-2021-47402 (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-2021-47402 linux Fixed in: 5.14.12-1
- Ubuntu UBUNTU-CVE-2021-47402 linux-hwe-edge
References
- patch git.kernel.org
- patch git.kernel.org
- patch git.kernel.org
- patch git.kernel.org