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CVE Record

CVE-2021-47132: mptcp: fix sk_forward_memory corruption on retransmission

In the Linux kernel, the following vulnerability has been resolved: mptcp: fix sk_forward_memory corruption on retransmission MPTCP sk_forward_memory handling is a bit special, as such field is protected by the msk socket spin_lock, instead of the plain socket lock. Currently we have a code path updating such field without handling the relevant lock: __mptcp_retrans() -> __mptcp_clean_una_wakeup() Several helpers in __mptcp_clean_una_wakeup() will update sk_forward_alloc, possibly causing such field corruption, as reported by Matthieu. Address the issue providing and using a new variant of blamed function which explicitly acquires the msk spin lock.

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysisunknown

Security readout for executives and security teams

Plain-English summary

This is a Linux kernel bug in Multipath TCP memory accounting during retransmission. A missing lock can corrupt socket forwarding memory state. The sources do not provide CVSS, impact detail, or evidence of active exploitation, so urgency depends on whether exposed systems run affected kernels with MPTCP in use.

Executive priority

Track and remediate through normal kernel patch management, with higher priority for infrastructure using MPTCP. There is not enough source evidence to justify emergency action solely from this CVE.

Technical view

The flaw is in MPTCP handling of sk_forward_memory/sk_forward_alloc during retransmission. A path through __mptcp_retrans() to __mptcp_clean_una_wakeup() updated memory accounting without the msk socket spin lock. The fix adds and uses a variant that explicitly takes the required lock.

Likely exposure

Likely limited to Linux systems running affected 5.12/5.13-era kernels or listed vulnerable commits where MPTCP is enabled or used. Distribution backports may change exposure, so confirm against the vendor kernel package rather than upstream version alone.

Exploitation context

The provided sources do not state active exploitation, KEV listing, exploit availability, attacker prerequisites, or reachable attack paths. Treat this as a kernel reliability and memory corruption risk until vendor-specific advisories clarify impact.

Researcher notes

The record describes a concurrency bug in MPTCP memory accounting protected by the wrong lock discipline. The public bundle lacks CVSS, CWE, exploitability analysis, and operational impact details, so validation should focus on kernel provenance and MPTCP usage.

Mitigation direction

  • Apply Linux kernel updates containing the referenced MPTCP locking fix.
  • Check your Linux distribution advisory for backported fixed kernel packages.
  • Prioritize systems where MPTCP is enabled or operationally required.
  • If no update is available, follow vendor guidance for temporary risk reduction.

Validation and detection

  • Inventory running Linux kernel versions across affected assets.
  • Confirm whether MPTCP is enabled or used by workloads.
  • Map installed kernels to vendor advisories or the referenced stable commits.
  • Review kernel crash or instability reports on systems using MPTCP.
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

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CVE-2021-47132 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

CISA-ADPCISA ADP Vulnrichment
other:ssvc
CVECVE Program Container

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinux64b9cea7a0afe579dd2682f1f1c04f2e4e72fd25, 64b9cea7a0afe579dd2682f1f1c04f2e4e72fd25, 96db8ffef07516a6d7414b6988f2a4298a839977unaffected
LinuxLinux5.12, 0, 5.12.10, 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.