CVE-2023-5215: Libnbd: crash or misbehaviour when nbd server returns an unexpected block size

Severity: medium (CVSS 6.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.8% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2023-09-28 · updated 2026-06-17
Weakness: CWE-241

Description

A flaw was found in libnbd. A server can reply with a block size larger than 2^63 (the NBD spec states the size is a 64-bit unsigned value). This issue could lead to an application crash or other unintended behavior for NBD clients that doesn't treat the return value of the nbd_get_size() function correctly.

Affected products

Red Hat Enterprise Linux: 8.0, 9.0
[UNKNOWN] libnbd: before 1.18.0 — fixed in 1.18.0

How to fix

Upgrade to a fixed version: [UNKNOWN] libnbd 1.18.0. Check the vendor advisory for mitigations.

References

https://access.redhat.com/errata/RHSA-2024:2204
https://access.redhat.com/security/cve/CVE-2023-5215
https://bugzilla.redhat.com/show_bug.cgi?id=2241041
https://listman.redhat.com/archives/libguestfs/2023-September/032635.html
https://access.redhat.com/errata/RHSA-2024:2204
https://access.redhat.com/security/cve/CVE-2023-5215
https://bugzilla.redhat.com/show_bug.cgi?id=2241041
https://listman.redhat.com/archives/libguestfs/2023-September/032635.html

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