Local privilege escalation via stale RACK PCB pointer
Published Aug 19, 2026 · Updated Aug 20, 2026
Use-after-free in the TCP RACK stack in FreeBSD allows local users to escalate privileges via crafted setsockopt calls. In the RACK setsockopt handler in sys/netinet/tcp_stacks/rack.c, the code drops the connection lock to copy option data from userspace, then reacquires the lock, verifies that the TCP stack identity still matches, but reuses a saved per-connection stack control-block pointer instead of reloading it; switching stacks twice in that window leaves the saved pointer dangling to freed memory. Exposure requires local code execution and tcp_rack.ko to be loaded, which FreeBSD states is not the default; affected release branches are 14.3 before p16, 14.4 before p7, 15.0 before p11, and 15.1 before p1.
Summary
What happened
Use-after-free in the TCP RACK stack in FreeBSD allows local users to escalate privileges via crafted setsockopt calls. In the RACK setsockopt handler in sys/netinet/tcp_stacks/rack.c, the code drops the connection lock to copy option data from userspace, then reacquires the lock, verifies that the TCP stack identity still matches, but reuses a saved per-connection stack control-block pointer instead of reloading it; switching stacks twice in that window leaves the saved pointer dangling to freed memory. Exposure requires local code execution and tcp_rack.ko to be loaded, which FreeBSD states is not the default; affected release branches are 14.3 before p16, 14.4 before p7, 15.0 before p11, and 15.1 before p1.
The record
- CVE
- CVE-2026-49422
- Published
- Aug 19, 2026
- Updated
- Aug 20, 2026
- Vendor
- The FreeBSD Project
- Product
- FreeBSD
- Classifications
- T1068
- Attack vector
- local
- Privileges
- authenticated
Timeline
How it unfolded
- Aug 19, 2026CVE publishedPublication date reported by the CVE source.
- Aug 20, 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=14.3-RELEASE <p16
- Affected versionversion=14.4-RELEASE <p7
- Affected versionversion=15.0-RELEASE <p11
- Affected versionversion=15.1-RELEASE <p1
What conditions does exploitation require?
What is affected?
Published CVSS scores
No CVSS assessment is available in this record.
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.
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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