What is CVE-2021-3716?

CVE-2021-3716 is a low-severity vulnerability in Nbdkit Project, classified under Improper Enforcement of Message Integrity During Transmission in a Communication Channel. CVSS score: 3.1/10. Published 2022-03-02.

How severe is CVE-2021-3716?

Low severity. CVSS v3 base score is 3.1 out of 10.

Is CVE-2021-3716 known to be exploited?

1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.

Vulnerability in Nbdkit Project

CVE-2021-3716

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.

Published 2022-03-02 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 3.1 (Low). Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L.

EPSS exploit prediction

EPSS: 0.006 (45.6th percentile), scored 2026-09-29.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 46th percentile — 45.6% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.006 · newest: 0.006 · change: 0.000

Affected products

Nbdkit Project
Red Hat Enterprise Linux — versions 8.0
Nbdkit — versions Affects nbdkit v1.12 through v1.26.4 | Fixedin nbdkit v1.26.5

Weakness classification (CWE)

CWE-924 — Improper Enforcement of Message Integrity During Transmission in a Communication Channel

Public proof-of-concept exploits

ARPSyndicate/cvemon

References

www.openwall.com/lists/oss-security/2021/08/18/2 (Mailing List, Third Party Advisory)
listman.redhat.com/archives/libguestfs/2021-August/msg00083.html (Broken Link)
gitlab.com/nbdkit/nbdkit/-/commit/09a13dafb7bb3a38ab52eb5501cba786365ba7fd (Patch, Third Party Advisory)
gitlab.com/nbdkit/nbdkit/-/commit/6c5faac6a37077cf2366388a80862bb00616d0d8 (Patch, Third Party Advisory)
bugzilla.redhat.com/show_bug.cgi (Patch, Third Party Advisory, Issue Tracking)

Frequently asked questions

What is CVE-2021-3716?: CVE-2021-3716 is a low-severity vulnerability in Nbdkit Project, classified under Improper Enforcement of Message Integrity During Transmission in a Communication Channel. CVSS score: 3.1/10. Published 2022-03-02.
How severe is CVE-2021-3716?: Low severity. CVSS v3 base score is 3.1 out of 10.
Is CVE-2021-3716 known to be exploited?: 1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.