Local privilege escalation via NBD reconnect use-after-free
Published Feb 27, 2025 · Updated Sep 8, 2026
Use-after-free in the Linux kernel NBD driver allows local users to gain elevated privileges by reconnecting a device after disconnect. nbd_genl_disconnect leaves NBD_RT_BOUND set after releasing the initial nbd_config reference, so nbd_genl_reconfigure can queue recv_work that decrements recv_threads after the configuration is freed. Reaching the flaw requires low-privileged local access and an NBD configuration whose disconnect and reconfigure operations race.
Summary
What happened
Use-after-free in the Linux kernel NBD driver allows local users to gain elevated privileges by reconnecting a device after disconnect. nbd_genl_disconnect leaves NBD_RT_BOUND set after releasing the initial nbd_config reference, so nbd_genl_reconfigure can queue recv_work that decrements recv_threads after the configuration is freed. Reaching the flaw requires low-privileged local access and an NBD configuration whose disconnect and reconfigure operations race.
The record
- CVE
- CVE-2025-21731
- Published
- Feb 27, 2025
- Updated
- Sep 8, 2026
- Vendor
- Siemens
- Product
- SIPLUS S7-1500 CPU 1518-4 PN/DP MFP
- Classifications
- CWE-416, T1068
- Attack vector
- local
- Privileges
- authenticated
Timeline
How it unfolded
- Feb 27, 2025CVE publishedPublication date reported by the CVE source.
- Sep 8, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
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- Affected versionversion=V3.1.6 <*
What conditions does exploitation require?
What is affected?
Published CVSS scores
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Attacks
What attackers are doing with it
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Public exploit references
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Technologies
Your stack
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Your stack
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