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Fencer Vulns
low 3.1

CVE-2021-3716 json

A flaw was found in nbdkit due to to improperly caching plaintext state across the STARTTLS encryption boundary.

published 2022-03-02 4 y ago modified 2026-06-17 4 mo ago also EUVD-2021-26997

cvss
3.1
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
0.6%
EPSS 0.6% chance of exploitation in 30 days, percentile 48%
public exploits
0
none known

Summary

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.

Patch / fix

  • nbdkit_project nbdkit 1.24.6, 1.26.5, 1.27.6
  • nbdkit Debian 14, Debian 13, Debian 12 1.26.5-1

debian advisories DEBIAN-CVE-2021-3716

  • SLOF RHEL 8 20210217-1.module+el8.6.0+14480+c0a3aa0f
  • hivex RHEL 8 1.3.18-23.module+el8.6.0+14480+c0a3aa0f
  • netcf RHEL 8 0.2.8-12.module+el8.6.0+14480+c0a3aa0f
  • swtpm RHEL 8 0.7.0-1.20211109gitb79fd91.module+el8.6.0+14480+c0a3aa0f
  • libnbd RHEL 8 1.6.0-5.module+el8.6.0+14480+c0a3aa0f
  • nbdkit RHEL 8 1.24.0-4.module+el8.6.0+14480+c0a3aa0f
  • libtpms RHEL 8 0.9.1-0.20211126git1ff6fe1f43.module+el8.6.0+14480+c0a3aa0f
  • libvirt RHEL 8 8.0.0-5.module+el8.6.0+14480+c0a3aa0f

red hat advisories RHSA-2022:1759RHSA-2022:0397

  • nbdkit openSUSE Tumbleweed 1.27.8-1.2

opensuse advisories openSUSE-SU-2024:11078-1

  • SLOF AlmaLinux 8 20210217-1.module_el8.6.0+2880+7d9e3703
  • hivex AlmaLinux 8 1.3.18-23.module_el8.6.0+2880+7d9e3703
  • netcf AlmaLinux 8 0.2.8-12.module_el8.6.0+2880+7d9e3703
  • swtpm AlmaLinux 8 0.7.0-1.20211109gitb79fd91.module_el8.6.0+2880+7d9e3703
  • libnbd AlmaLinux 8 1.6.0-5.module_el8.6.0+2880+7d9e3703
  • nbdkit AlmaLinux 8 1.24.0-4.module_el8.6.0+2880+7d9e3703
  • libtpms AlmaLinux 8 0.9.1-0.20211126git1ff6fe1f43.module_el8.6.0+2880+7d9e3703
  • libvirt AlmaLinux 8 8.0.0-5.module_el8.6.0+2880+7d9e3703

almalinux advisories ALSA-2022:1759

  • hivex Rocky Linux 8 1.3.18-23.module+el8.7.0+1084+97b81f61
  • hivex Rocky Linux 8 1.3.18-23.module+el8.6.0+847+b490afdd
  • netcf Rocky Linux 8 0.2.8-12.module+el8.7.0+1084+97b81f61
  • netcf Rocky Linux 8 0.2.8-12.module+el8.4.0+534+4680a14e
  • netcf Rocky Linux 8 0.2.8-12.module+el8.6.0+847+b490afdd
  • swtpm Rocky Linux 8 0.7.0-1.20211109gitb79fd91.module+el8.6.0+847+b490afdd
  • libnbd Rocky Linux 8 1.6.0-5.module+el8.7.0+1084+97b81f61
  • libnbd Rocky Linux 8 1.6.0-5.module+el8.6.0+847+b490afdd

rocky linux advisories RLSA-2022:1759

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2021-3716 updated cvss 3.5

nbdkit: NBD_OPT_STRUCTURED_REPLY injection on STARTTLS

  • Red Hat Enterprise Linux 8 Advanced Virtualization nbdkit, nbdkit-server, nbdkit-plugin-xz, nbdkit-xz-filter, nbdkit-nbd-plugin, nbdkit-ssh-plugin, +17 more
    affected: workaround, no fix available, no fix planned “Out of support scope”
  • Red Hat Advanced Virtualization for RHEL 8.5.0.Z netcf 0.2.8-12.module+el8.4.0+8855+a9e237a9, libnbd 1.6.0-4.module+el8.5.0+11638+3d8f9850, hivex 1.3.18-22.module+el8.5.0+12087+2208d04c, libvirt 7.6.0-6.module+el8.5.0+13051+7ddbe958, nbdfuse 1.6.0-4.module+el8.5.0+11638+3d8f9850, nbdkit 1.24.0-3.module+el8.5.0+13900+a08c0464, +110 more
    fixed: vendor fix RHSA-2022:0397
  • Red Hat Enterprise Linux AppStream (v. 8) libnbd 1.6.0-5.module+el8.6.0+14480+c0a3aa0f, netcf 0.2.8-12.module+el8.6.0+14480+c0a3aa0f, hivex 1.3.18-23.module+el8.6.0+14480+c0a3aa0f, libvirt 8.0.0-5.module+el8.6.0+14480+c0a3aa0f, nbdfuse 1.6.0-5.module+el8.6.0+14480+c0a3aa0f, nbdkit 1.24.0-4.module+el8.6.0+14480+c0a3aa0f, +104 more Red Hat Enterprise Linux CRB (v. 8) libnbd 1.6.0-5.module+el8.6.0+14480+c0a3aa0f, netcf 0.2.8-12.module+el8.6.0+14480+c0a3aa0f, hivex 1.3.18-23.module+el8.6.0+14480+c0a3aa0f, libvirt 8.0.0-5.module+el8.6.0+14480+c0a3aa0f, nbdfuse 1.6.0-5.module+el8.6.0+14480+c0a3aa0f, SLOF 20210217-1.module+el8.6.0+14480+c0a3aa0f, +38 more
    fixed: vendor fix RHSA-2022:1759
  • Red Hat Enterprise Linux 7 nbdkit, nbdkit-plugin-vddk, nbdkit-basic-plugins, nbdkit-plugin-python2, nbdkit-example-plugins, nbdkit-plugin-python-common Red Hat Enterprise Linux 9 nbdkit, nbdkit-server, nbdkit-selinux, nbdkit-xz-filter, nbdkit-nbd-plugin, nbdkit-ssh-plugin, +12 more Red Hat Virtualization 4 nbdkit
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

0.58% chance of exploitation in the next 30 days, higher than 48% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
NVD 3.1 3.1 CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L
NVD 2.0 3.5 AV:N/AC:M/Au:S/C:N/I:N/A:P

Affected products

  • n/a nbdkit

Classification

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

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.