LiveActive security incident?Get immediate response
CVE Record

CVE-2021-47588: sit: do not call ipip6_dev_free() from sit_init_net()

In the Linux kernel, the following vulnerability has been resolved: sit: do not call ipip6_dev_free() from sit_init_net() ipip6_dev_free is sit dev->priv_destructor, already called by register_netdevice() if something goes wrong. Alternative would be to make ipip6_dev_free() robust against multiple invocations, but other drivers do not implement this strategy. syzbot reported: dst_release underflow WARNING: CPU: 0 PID: 5059 at net/core/dst.c:173 dst_release+0xd8/0xe0 net/core/dst.c:173 Modules linked in: CPU: 1 PID: 5059 Comm: syz-executor.4 Not tainted 5.16.0-rc5-syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 RIP: 0010:dst_release+0xd8/0xe0 net/core/dst.c:173 Code: 4c 89 f2 89 d9 31 c0 5b 41 5e 5d e9 da d5 44 f9 e8 1d 90 5f f9 c6 05 87 48 c6 05 01 48 c7 c7 80 44 99 8b 31 c0 e8 e8 67 29 f9 <0f> 0b eb 85 0f 1f 40 00 53 48 89 fb e8 f7 8f 5f f9 48 83 c3 a8 48 RSP: 0018:ffffc9000aa5faa0 EFLAGS: 00010246 RAX: d6894a925dd15a00 RBX: 00000000ffffffff RCX: 0000000000040000 RDX: ffffc90005e19000 RSI: 000000000003ffff RDI: 0000000000040000 RBP: 0000000000000000 R08: ffffffff816a1f42 R09: ffffed1017344f2c R10: ffffed1017344f2c R11: 0000000000000000 R12: 0000607f462b1358 R13: 1ffffffff1bfd305 R14: ffffe8ffffcb1358 R15: dffffc0000000000 FS: 00007f66c71a2700(0000) GS:ffff8880b9a00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007f88aaed5058 CR3: 0000000023e0f000 CR4: 00000000003506f0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: <TASK> dst_cache_destroy+0x107/0x1e0 net/core/dst_cache.c:160 ipip6_dev_free net/ipv6/sit.c:1414 [inline] sit_init_net+0x229/0x550 net/ipv6/sit.c:1936 ops_init+0x313/0x430 net/core/net_namespace.c:140 setup_net+0x35b/0x9d0 net/core/net_namespace.c:326 copy_net_ns+0x359/0x5c0 net/core/net_namespace.c:470 create_new_namespaces+0x4ce/0xa00 kernel/nsproxy.c:110 unshare_nsproxy_namespaces+0x11e/0x180 kernel/nsproxy.c:226 ksys_unshare+0x57d/0xb50 kernel/fork.c:3075 __do_sys_unshare kernel/fork.c:3146 [inline] __se_sys_unshare kernel/fork.c:3144 [inline] __x64_sys_unshare+0x34/0x40 kernel/fork.c:3144 do_syscall_x64 arch/x86/entry/common.c:50 [inline] do_syscall_64+0x44/0xd0 arch/x86/entry/common.c:80 entry_SYSCALL_64_after_hwframe+0x44/0xae RIP: 0033:0x7f66c882ce99 Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 bc ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007f66c71a2168 EFLAGS: 00000246 ORIG_RAX: 0000000000000110 RAX: ffffffffffffffda RBX: 00007f66c893ff60 RCX: 00007f66c882ce99 RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000048040200 RBP: 00007f66c8886ff1 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 R13: 00007fff6634832f R14: 00007f66c71a2300 R15: 0000000000022000 </TASK>

UnknownCVSS not scoredNot KEV-listedUpdated
Discuss exposureBack to CVEs
Glexia's TakeAutomated analysisunknown

Security readout for executives and security teams

Plain-English summary

CVE-2021-47588 is a Linux kernel networking bug in the SIT IPv6-over-IPv4 tunnel code. The source shows a cleanup routine could be called twice during network namespace setup failure, causing a destination-cache release underflow warning. No CVSS score, CWE, confirmed real-world exploitation, or business impact is provided in the source bundle.

Executive priority

Treat this as a kernel maintenance item unless vendor guidance raises impact. There is no confirmed exploitation or severity score in the provided sources, but kernel bugs can affect platform stability. Prioritize patch validation on multi-tenant Linux systems and hosts where untrusted workloads can create namespaces.

Technical view

The issue is in net/ipv6/sit.c: sit_init_net() called ipip6_dev_free(), but that function is already registered as the device private destructor and can be invoked by register_netdevice() on failure. Syzbot observed dst_release underflow through dst_cache_destroy() during namespace creation. Kernel stable commits remove the duplicate destructor call.

Likely exposure

Exposure is most relevant to Linux systems running the affected kernel versions or downstream kernels carrying the vulnerable SIT driver code. The trace involves network namespace creation and SIT tunnel initialization. The provided data does not establish remote reachability, required privileges, or whether common distribution kernels are affected.

Exploitation context

The source only cites a syzbot report and kernel fix commits. CISA KEV status is false, and no cited source states active exploitation. The trace shows a local kernel path involving unshare and network namespace setup, but the bundle does not provide exploitability details.

Researcher notes

Evidence is limited to the CVE record, syzbot trace, and kernel stable commits. The probable flaw class is duplicate cleanup/destructor invocation causing dst cache reference underflow. Do not assume privilege escalation, remote attack, or crash impact without additional vendor or kernel maintainer evidence.

Mitigation direction

  • Update affected Linux kernels to vendor releases containing the referenced stable fixes.
  • Check distribution advisories for backported fixes matching CVE-2021-47588.
  • Prioritize systems allowing untrusted users to create network namespaces.
  • Review whether SIT tunnel support is enabled where unnecessary.
  • Track kernel vendor guidance if no packaged update is available.

Validation and detection

  • Inventory kernel versions across Linux hosts and containers infrastructure.
  • Compare installed kernels against vendor advisories for CVE-2021-47588.
  • Confirm patched kernels include the referenced upstream stable commits or backports.
  • Review kernel logs for dst_release underflow warnings during namespace operations.
  • Validate namespace creation policy for untrusted users.
Prepared
Confidence
medium
Sources
8

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

Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.

cve · low confidence lookup

CVE-2021-47588 mapping review

Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.

Open ATT&CK lookup
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
7Source 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

CVECVE Program Container
CISA-ADPCISA ADP Vulnrichment
other:ssvc

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinuxcf124db566e6b036b8bcbe8decbed740bdfac8c6, cf124db566e6b036b8bcbe8decbed740bdfac8c6, cf124db566e6b036b8bcbe8decbed740bdfac8c6, cf124db566e6b036b8bcbe8decbed740bdfac8c6, cf124db566e6b036b8bcbe8decbed740bdfac8c6, cf124db566e6b036b8bcbe8decbed740bdfac8c6, 95876855a55072572895a236b156ffb357fd5538unaffected
LinuxLinux4.12, 0, 4.14.259, 4.19.222, 5.4.168, 5.10.88, 5.15.11, 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.