Kernel compromise via ksmbd connection use-after-free
Published Apr 1, 2025 · Updated Aug 5, 2026
Use-after-free in affected Linux kernel ksmbd releases allows remote authenticated users to compromise the kernel through SMB2 traffic. During an oplock break, work continues after a connection and its transport are released because the reference count does not cover the pending request, leaving ksmbd_conn_write to dereference freed state. A low-privileged SMB share session or guest mapping and two attacker-controlled connections are required; reclaimed state enables kernel-memory access and control-flow hijacking, while a stale dereference can panic the host.
Summary
What happened
Use-after-free in affected Linux kernel ksmbd releases allows remote authenticated users to compromise the kernel through SMB2 traffic. During an oplock break, work continues after a connection and its transport are released because the reference count does not cover the pending request, leaving ksmbd_conn_write to dereference freed state. A low-privileged SMB share session or guest mapping and two attacker-controlled connections are required; reclaimed state enables kernel-memory access and control-flow hijacking, while a stale dereference can panic the host.
The record
- CVE
- CVE-2025-21955
- Published
- Apr 1, 2025
- Updated
- Aug 5, 2026
- Vendor
- The Linux Kernel Organization
- Product
- Linux
- Classifications
- T1210
- Attack vector
- network
- Privileges
- authenticated
Timeline
How it unfolded
- Apr 1, 2025CVE publishedPublication date reported by the CVE source.
- Aug 5, 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?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=0626e6641f6b467447c81dd7678a69c66f7746cf <09aeab68033161cb54f194da93e51a11aee6144b
- Affected versionversion=0626e6641f6b467447c81dd7678a69c66f7746cf <3aa660c059240e0c795217182cf7df32909dd917
- Affected versionversion=0626e6641f6b467447c81dd7678a69c66f7746cf <a4261bbc33fbf99b99c80aa3a2c5097611802980
- Affected versionversion=0626e6641f6b467447c81dd7678a69c66f7746cf <f17d1c63a76b0fe8e9c78023a86507a3a6d62cfa
- Affected versionversion=5.15
What conditions does exploitation require?
What is affected?
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.
Weakness, pattern, technique
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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