CVE-2021-20286Network attack vector

Client process crash via incomplete option replies

Published Mar 15, 2021 · Updated Aug 3, 2024

Reachable assertion in Red Hat libnbd 1.7.3 allows remote attackers controlling an NBD server to crash a client during option negotiation. In nbd_unlocked_opt_go and nbd_unlocked_opt_info, an incomplete NBD_OPT_GO or NBD_OPT_INFO reply can leave the next state dead, but the code asserts that it remains negotiating. The client must enable option mode and connect to an attacker-controlled or compromised NBD server; the consequence is termination of the consuming process.

CVSS severity2.7
Low
EPSS probability1.14%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Reachable assertion in Red Hat libnbd 1.7.3 allows remote attackers controlling an NBD server to crash a client during option negotiation. In nbd_unlocked_opt_go and nbd_unlocked_opt_info, an incomplete NBD_OPT_GO or NBD_OPT_INFO reply can leave the next state dead, but the code asserts that it remains negotiating. The client must enable option mode and connect to an attacker-controlled or compromised NBD server; the consequence is termination of the consuming process.

The record

CVE
CVE-2021-20286
Published
Mar 15, 2021
Updated
Aug 3, 2024
Vendor
Red Hat
Product
libnbd
Classifications
CWE-617, T1499.004
Attack vector
network
Privileges
Unavailable

Timeline

How it unfolded

  1. Mar 15, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=libnbd 1.7.3

What conditions does exploitation require?

Attack vectornetwork
Required privilegesUnavailable in this record.

What is affected?

Red Hat · libnbdversion=libnbd 1.7.3

Published CVSS scores

4.0NIST NVDAV:N/AC:L/Au:S/C:N/I:N/A:P
2.7NIST NVDCVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:L

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
PrivilegesUnavailable
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-617Reachable Assertion
T1499.004Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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