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CVE Record

CVE-2021-47082: tun: avoid double free in tun_free_netdev

In the Linux kernel, the following vulnerability has been resolved: tun: avoid double free in tun_free_netdev Avoid double free in tun_free_netdev() by moving the dev->tstats and tun->security allocs to a new ndo_init routine (tun_net_init()) that will be called by register_netdevice(). ndo_init is paired with the desctructor (tun_free_netdev()), so if there's an error in register_netdevice() the destructor will handle the frees. BUG: KASAN: double-free or invalid-free in selinux_tun_dev_free_security+0x1a/0x20 security/selinux/hooks.c:5605 CPU: 0 PID: 25750 Comm: syz-executor416 Not tainted 5.16.0-rc2-syzk #1 Hardware name: Red Hat KVM, BIOS Call Trace: <TASK> __dump_stack lib/dump_stack.c:88 [inline] dump_stack_lvl+0x89/0xb5 lib/dump_stack.c:106 print_address_description.constprop.9+0x28/0x160 mm/kasan/report.c:247 kasan_report_invalid_free+0x55/0x80 mm/kasan/report.c:372 ____kasan_slab_free mm/kasan/common.c:346 [inline] __kasan_slab_free+0x107/0x120 mm/kasan/common.c:374 kasan_slab_free include/linux/kasan.h:235 [inline] slab_free_hook mm/slub.c:1723 [inline] slab_free_freelist_hook mm/slub.c:1749 [inline] slab_free mm/slub.c:3513 [inline] kfree+0xac/0x2d0 mm/slub.c:4561 selinux_tun_dev_free_security+0x1a/0x20 security/selinux/hooks.c:5605 security_tun_dev_free_security+0x4f/0x90 security/security.c:2342 tun_free_netdev+0xe6/0x150 drivers/net/tun.c:2215 netdev_run_todo+0x4df/0x840 net/core/dev.c:10627 rtnl_unlock+0x13/0x20 net/core/rtnetlink.c:112 __tun_chr_ioctl+0x80c/0x2870 drivers/net/tun.c:3302 tun_chr_ioctl+0x2f/0x40 drivers/net/tun.c:3311 vfs_ioctl fs/ioctl.c:51 [inline] __do_sys_ioctl fs/ioctl.c:874 [inline] __se_sys_ioctl fs/ioctl.c:860 [inline] __x64_sys_ioctl+0x19d/0x220 fs/ioctl.c:860 do_syscall_x64 arch/x86/entry/common.c:50 [inline] do_syscall_64+0x3a/0x80 arch/x86/entry/common.c:80 entry_SYSCALL_64_after_hwframe+0x44/0xae

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysisunknown

Security readout for executives and security teams

Plain-English summary

This Linux kernel flaw is a double-free bug in the TUN/TAP network driver cleanup path. The provided sources show a kernel crash found by fuzzing, but no CVSS score, named real-world attacks, or KEV listing. Treat it as a kernel stability and potential privilege-risk issue until vendor guidance confirms impact.

Executive priority

Handle through normal kernel patch governance unless your environment exposes TUN/TAP to untrusted local users or workloads. The absence of known exploitation lowers urgency, but kernel memory-management bugs should not be deferred indefinitely.

Technical view

CVE-2021-47082 affects Linux TUN driver cleanup in tun_free_netdev(). Allocations for dev->tstats and tun->security were moved into ndo_init so register_netdevice() failure paths pair correctly with the destructor. The trace shows KASAN detecting double-free or invalid-free through SELinux TUN security cleanup.

Likely exposure

Exposure is most relevant to Linux systems running affected kernel versions with TUN/TAP support. The bundle lists affected Linux versions and stable kernel fixes, but does not define exact distribution packages, privilege requirements, or reachable attack scenarios.

Exploitation context

The source bundle shows a syzkaller/KASAN crash trace and kernel stable fixes. It does not provide evidence of active exploitation, public exploit use, or CISA KEV inclusion. Exploitability and business impact remain unclear from the supplied evidence.

Researcher notes

The strongest evidence is the upstream kernel fix description and KASAN trace. Affected-version metadata is broad and partly commit-based. The bundle does not include CVSS, CWE mapping, distribution advisories, proof of exploitation, or precise prerequisites.

Mitigation direction

  • Check distribution kernel advisories for CVE-2021-47082 package status.
  • Update affected Linux kernels to a vendor-fixed build.
  • Prioritize systems allowing local users or services to use TUN/TAP interfaces.
  • Restrict unnecessary access to TUN/TAP functionality where operationally feasible.
  • Track kernel stable commits referenced by the CVE for backport confirmation.

Validation and detection

  • Inventory Linux kernel versions across servers, appliances, and images.
  • Compare installed kernels against vendor advisories for CVE-2021-47082.
  • Confirm whether TUN/TAP support is enabled on exposed systems.
  • Review whether untrusted workloads can request TUN/TAP devices.
  • Verify patched systems are running the updated kernel after reboot.
Prepared
Confidence
medium
Sources
7

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

ATT&CK lookup starting points

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CVE-2021-47082 mapping review

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Vulnerability profileCVE Program record
Severity
Unknown
CVSS
Not scored
Known Exploited
No
Published
Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

0CVSS vectors
3Timeline events
2ADP providers
6Source links

SSVC decision data

CISA-ADPCISA Coordinator
Timestamp
Version
2.0.3
Exploitation: noneAutomatable: noTechnical Impact: partial

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. CVE publishedCVE Program

    The CVE record was published.

  3. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

ADP provider summaries

CISA-ADPCISA ADP Vulnrichment
other:ssvc
CVECVE Program Container

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinux662ca437e714caaab855b12415d6ffd815985bc0, 662ca437e714caaab855b12415d6ffd815985bc0, 662ca437e714caaab855b12415d6ffd815985bc0, 662ca437e714caaab855b12415d6ffd815985bc0, 662ca437e714caaab855b12415d6ffd815985bc0, a81a02460bdf054ca0c60c5aed29941f7134092d, 6fc265f7a86d81e052508d03da555188f5882c3eunaffected
LinuxLinux3.12, 0, 4.19.280, 5.4.240, 5.10.136, 5.15.12, 5.16affected
Weakness

CWE details

No CWE listed

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.