CVE-2021-3716

Name: CVE-2021-3716
Creator: NVD / NIST
Published: 2022-03-02T23:15:09.013+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

LOWCVSS 3.1/10EPSS 0.56%

Last modified Jun 17, 2026

CVE-2021-3716 is a low-severity vulnerability rated 3.1/10 on the CVSS scale. 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. EPSS estimates a 0.56% chance of exploitation in the next 30 days.

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.

Metrics

CVSS 3.1

3.1/10

CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L

EPSS Probability

0.56%

42.1th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-924

Affected Software

Vendor	Product	Versions
Nbdkit Project	Nbdkit	>= 1.11.8, < 1.24.6
Nbdkit Project	Nbdkit	>= 1.25.1, < 1.26.5
Nbdkit Project	Nbdkit	>= 1.27.1, < 1.27.6
Redhat	Enterprise Linux	8.0

References

https://bugzilla.redhat.com/show_bug.cgi?id=1994695Issue Tracking, Patch, Third Party Advisory
https://gitlab.com/nbdkit/nbdkit/-/commit/09a13dafb7bb3a38ab52eb5501cba786365ba7fdPatch, Third Party Advisory
https://gitlab.com/nbdkit/nbdkit/-/commit/6c5faac6a37077cf2366388a80862bb00616d0d8Patch, Third Party Advisory
https://listman.redhat.com/archives/libguestfs/2021-August/msg00083.htmlBroken Link
https://www.openwall.com/lists/oss-security/2021/08/18/2Mailing List, Third Party Advisory
https://bugzilla.redhat.com/show_bug.cgi?id=1994695Issue Tracking, Patch, Third Party Advisory
https://gitlab.com/nbdkit/nbdkit/-/commit/09a13dafb7bb3a38ab52eb5501cba786365ba7fdPatch, Third Party Advisory
https://gitlab.com/nbdkit/nbdkit/-/commit/6c5faac6a37077cf2366388a80862bb00616d0d8Patch, Third Party Advisory
https://listman.redhat.com/archives/libguestfs/2021-August/msg00083.htmlBroken Link
https://www.openwall.com/lists/oss-security/2021/08/18/2Mailing List, Third Party Advisory

Timeline

Published: Mar 2, 2022
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-3716?

How severe is CVE-2021-3716?

CVE-2021-3716 has a CVSS score of 3.1/10 (LOW severity). The EPSS model estimates a 0.56% probability of exploitation in the next 30 days.

How do I fix CVE-2021-3716?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2021-3716?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST