Security readout for executives and security teams
Plain-English summary
CVE-2021-47370 is a Linux kernel MPTCP bug where certain send operations could create network buffers missing required MPTCP metadata. The public record shows syzbot triggering a kernel warning. It does not show active exploitation, data theft, privilege escalation, or a remote attacker scenario.
Executive priority
Treat this as a routine kernel maintenance issue unless your environment depends on MPTCP or vendor advisories raise severity. There is not enough public evidence here to justify emergency response, but affected kernels should be brought onto supported fixed releases.
Technical view
The flaw is in Linux kernel MPTCP transmit handling. A signed/unsigned comparison could incorrectly treat an undersized size goal as positive, skip transmit-cache refill, and allow a TCP-allocated skb without required MPTCP extensions to reach mptcp_sendmsg_frag, triggering WARN_ON(). Stable kernel commits rewrite the expression and ensure cached tx skbs carry the extension.
Likely exposure
Exposure is limited to Linux kernels containing the affected MPTCP code path. The bundle lists Linux as the product and provides fixed stable commits, but does not clearly enumerate vulnerable released versions, deployment prerequisites, or whether MPTCP must be enabled at runtime.
Exploitation context
CISA KEV status is false, and the supplied sources only describe syzbot reproduction of a WARN_ON() in a test kernel. There is no cited evidence of public weaponization, in-the-wild exploitation, required privileges, or remote exploitability.
Researcher notes
The public detail supports a correctness bug in MPTCP skb extension handling, found by syzbot. Key gaps are vulnerable version range, security impact beyond WARN_ON(), reachability requirements, and distro backport mapping. Avoid assuming denial of service or privilege impact without vendor confirmation.
Mitigation direction
- Check your Linux distribution advisory for CVE-2021-47370 package status.
- Update to a kernel build containing the referenced stable fixes.
- Prioritize systems where MPTCP is enabled or used.
- If patching is delayed, follow vendor guidance; no source-provided workaround is identified.
Validation and detection
- Map installed kernel packages to vendor advisories for CVE-2021-47370.
- Confirm whether deployed kernels include the referenced stable commits.
- Check whether MPTCP support is enabled on relevant systems.
- Review kernel logs for similar MPTCP WARN_ON() events as diagnostic signals.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
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-2021-47370 mapping review
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Open ATT&CK lookup- Severity
- Unknown
- CVSS
- Not scored
- Known Exploited
- No
- Published
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.
SSVC decision data
Vulnerability timeline
Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.
- CVE reservedCVE Program
The CVE ID was reserved by the assigning CNA.
- CVE publishedCVE Program
The CVE record was published.
- CVE updatedCVE Program
The CVE record metadata indicates this as the latest update time.
ADP provider summaries
Source materials
- CVE List V5 sourceCVE List V5
- https://git.kernel.org/stable/c/f8ff625a8082db8c2b58dcb5229b27928943b94bCVE reference, Linux
- https://git.kernel.org/stable/c/977d293e23b48a1129830d7968605f61c4af71a0CVE reference, Linux
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.