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CVE Record

CVE-2021-47001: xprtrdma: Fix cwnd update ordering

In the Linux kernel, the following vulnerability has been resolved: xprtrdma: Fix cwnd update ordering After a reconnect, the reply handler is opening the cwnd (and thus enabling more RPC Calls to be sent) /before/ rpcrdma_post_recvs() can post enough Receive WRs to receive their replies. This causes an RNR and the new connection is lost immediately. The race is most clearly exposed when KASAN and disconnect injection are enabled. This slows down rpcrdma_rep_create() enough to allow the send side to post a bunch of RPC Calls before the Receive completion handler can invoke ib_post_recv().

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysisunknown

Security readout for executives and security teams

Plain-English summary

CVE-2021-47001 is a Linux kernel RPC-over-RDMA reliability flaw. After a reconnect, the kernel can send more RPC calls before enough receive buffers are posted, causing the new RDMA connection to fail immediately. The sources do not provide CVSS, CWE, or confirmed attack activity.

Executive priority

Treat this as targeted operational risk, not a broad emergency, unless your environment depends on RDMA-backed Linux storage or NetApp-advised products. Prioritize exposure discovery and patch through normal kernel maintenance, accelerating for critical NFS-over-RDMA workloads.

Technical view

The resolved Linux kernel bug is in xprtrdma cwnd update ordering. The reply handler opens the congestion window before rpcrdma_post_recvs() posts sufficient Receive Work Requests. Under timing stress, this can trigger RNR and drop the reconnected transport. The issue is most visible with KASAN and disconnect injection enabled.

Likely exposure

Exposure appears limited to Linux systems using RPC-over-RDMA, such as NFS over RDMA or products embedding affected Linux kernels. The bundle lists Linux 5.5 through 5.13-related affected ranges and stable kernel commits, but it does not map all downstream distro packages or appliances.

Exploitation context

No source in the bundle reports active exploitation, and KEV status is false. The description reads like a race condition causing connection loss after reconnect rather than a documented remote code execution path. Evidence is incomplete on practical attacker control, prerequisites, and business impact.

Researcher notes

The strongest evidence is the Linux kernel resolution text and stable commit references. Missing CVSS, CWE, and exploitability analysis limit confidence in impact ranking. Focus validation on code lineage, downstream backports, and whether the xprtrdma path is reachable in production.

Mitigation direction

  • Check Linux vendor or distribution guidance for backported fixes.
  • Upgrade to a kernel containing the referenced xprtrdma stable fixes.
  • Identify and prioritize systems using RPC-over-RDMA or NFS over RDMA.
  • Review NetApp advisory applicability for affected storage environments.
  • Monitor for reconnect-related RDMA or NFS service instability until patched.

Validation and detection

  • Inventory Linux kernel versions on RDMA-capable servers and appliances.
  • Confirm whether RPC-over-RDMA or NFS over RDMA is enabled.
  • Verify installed kernel packages include the xprtrdma cwnd ordering fix.
  • Review logs for RDMA RNR, reconnect, or transport-loss symptoms.
  • Track vendor advisories for downstream package or appliance status.
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-2021-47001 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
LinuxLinux2ae50ad68cd79224198b525f7bd645c9da98b6ff, 2ae50ad68cd79224198b525f7bd645c9da98b6ff, 2ae50ad68cd79224198b525f7bd645c9da98b6ff, 2ae50ad68cd79224198b525f7bd645c9da98b6ff, 3791c5982ba1eebf2900ee7ca7b9a89619c26d54unaffected
LinuxLinux5.5, 0, 5.10.38, 5.11.22, 5.12.5, 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.