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CVE Record

CVE-2021-47014: net/sched: act_ct: fix wild memory access when clearing fragments

In the Linux kernel, the following vulnerability has been resolved: net/sched: act_ct: fix wild memory access when clearing fragments while testing re-assembly/re-fragmentation using act_ct, it's possible to observe a crash like the following one: KASAN: maybe wild-memory-access in range [0x0001000000000448-0x000100000000044f] CPU: 50 PID: 0 Comm: swapper/50 Tainted: G S 5.12.0-rc7+ #424 Hardware name: Dell Inc. PowerEdge R730/072T6D, BIOS 2.4.3 01/17/2017 RIP: 0010:inet_frag_rbtree_purge+0x50/0xc0 Code: 00 fc ff df 48 89 c3 31 ed 48 89 df e8 a9 7a 38 ff 4c 89 fe 48 89 df 49 89 c6 e8 5b 3a 38 ff 48 8d 7b 40 48 89 f8 48 c1 e8 03 <42> 80 3c 20 00 75 59 48 8d bb d0 00 00 00 4c 8b 6b 40 48 89 f8 48 RSP: 0018:ffff888c31449db8 EFLAGS: 00010203 RAX: 0000200000000089 RBX: 000100000000040e RCX: ffffffff989eb960 RDX: 0000000000000140 RSI: ffffffff97cfb977 RDI: 000100000000044e RBP: 0000000000000900 R08: 0000000000000000 R09: ffffed1186289350 R10: 0000000000000003 R11: ffffed1186289350 R12: dffffc0000000000 R13: 000100000000040e R14: 0000000000000000 R15: ffff888155e02160 FS: 0000000000000000(0000) GS:ffff888c31440000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00005600cb70a5b8 CR3: 0000000a2c014005 CR4: 00000000003706e0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: <IRQ> inet_frag_destroy+0xa9/0x150 call_timer_fn+0x2d/0x180 run_timer_softirq+0x4fe/0xe70 __do_softirq+0x197/0x5a0 irq_exit_rcu+0x1de/0x200 sysvec_apic_timer_interrupt+0x6b/0x80 </IRQ> when act_ct temporarily stores an IP fragment, restoring the skb qdisc cb results in putting random data in FRAG_CB(), and this causes those "wild" memory accesses later, when the rbtree is purged. Never overwrite the skb cb in case tcf_ct_handle_fragments() returns -EINPROGRESS.

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

This is a Linux kernel memory-safety bug in packet fragmentation handling for the traffic-control conntrack action. In the reported case, it caused a kernel crash during fragment cleanup. Business urgency depends on whether affected kernels use act_ct with fragmented traffic; the bundle provides no CVSS score or active exploitation evidence.

Executive priority

Handle as a targeted kernel stability risk, not a broad emergency based on current evidence. Prioritize internet-facing or high-throughput network nodes using act_ct, and fold remediation into kernel maintenance unless local exposure is confirmed.

Technical view

When tcf_ct_handle_fragments() temporarily stores an IP fragment and returns -EINPROGRESS, act_ct could restore skb qdisc control-block data and corrupt FRAG_CB(). Later inet_frag_rbtree_purge could dereference invalid memory, producing KASAN wild-memory-access and crash evidence.

Likely exposure

Exposure is most likely on Linux systems running affected kernel versions that use net/sched act_ct for connection tracking and process IP fragments. Systems not using this kernel path are less likely exposed. The source bundle does not identify distributions, configurations, or cloud products.

Exploitation context

The bundle says KEV is false and gives no evidence of active exploitation. The only demonstrated context is testing of reassembly and refragmentation using act_ct that produced a crash. Treat exploitability beyond denial of service as unproven from these sources.

Researcher notes

Key condition is act_ct fragment handling returning -EINPROGRESS, followed by qdisc skb control-block restoration corrupting fragment metadata. The source data lacks CVSS, CWE, exploit details, and distribution-specific affected ranges, so validation should be configuration-led.

Mitigation direction

  • Update to a vendor-supported Linux kernel containing the referenced stable fixes.
  • Prioritize systems using traffic-control conntrack actions with fragmented traffic exposure.
  • Check distribution advisories for backported fixes before relying on upstream version numbers.
  • Reduce unnecessary exposure of fragment-heavy traffic paths where operationally feasible.

Validation and detection

  • Inventory Linux kernel versions across affected hosts.
  • Confirm whether traffic-control rules use act_ct on those hosts.
  • Verify vendor kernel changelogs include the referenced upstream stable commits.
  • Review crash telemetry for inet_frag_rbtree_purge or related KASAN reports.
Prepared
Confidence
medium
Sources
4

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-2021-47014 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
3Source 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
LinuxLinuxae372cb1750f6c95370f92fe5f5620e0954663ba, ae372cb1750f6c95370f92fe5f5620e0954663ba, fbff97eb6f4a94a3f15f685bed604c9adc29ac3eunaffected
LinuxLinux5.8, 0, 5.12.4, 5.13affected
Weakness

CWE details

No CWE listed

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