CVE-2023-5871Public exploitNetwork attack vector

Client crash via oversized block-status flag

Published Nov 27, 2023 · Updated Nov 20, 2025

Reachable assertion in libnbd on Red Hat Enterprise Linux 9 allows remote attackers controlling an NBD server to crash the client process. During nbd_block_status(), the 32-bit client API asserts instead of returning EOVERFLOW when an extended-header reply carries a flag above 32 bits. The client must negotiate 64-bit extended headers, use the legacy API, and request block status; the denial of service terminates only the calling process.

CVSS severity5.3
Medium
EPSS probability0.92%
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 libnbd on Red Hat Enterprise Linux 9 allows remote attackers controlling an NBD server to crash the client process. During nbd_block_status(), the 32-bit client API asserts instead of returning EOVERFLOW when an extended-header reply carries a flag above 32 bits. The client must negotiate 64-bit extended headers, use the legacy API, and request block status; the denial of service terminates only the calling process.

The record

CVE
CVE-2023-5871
Published
Nov 27, 2023
Updated
Nov 20, 2025
Vendor
Red Hat
Product
Red Hat Enterprise Linux 9
Classifications
CWE-617, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Nov 27, 2023CVE publishedPublication date reported by the CVE source.
  2. Nov 20, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected versions are unavailable in this record. Check the vendor advisory for version and patch details.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Red Hat · Red Hat Enterprise Linux 9Affected versions are unavailable in this record.

Published CVSS scores

5.3Red HatCVSS:3.1/AV:N/AC:L/PR:N/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 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

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

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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