CVE-2026-63979
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedIn the Linux kernel, the following vulnerability has been resolved: net/handshake: hand off the pinned file reference to accept_doit handshake_req_next() removes the request from the per-net pending list and drops hn_lock before handshake_nl_accept_doit() reads req->hr_sk->sk_socket and dereferences sock->file (once in FD_PREPARE() and again in get_file()). In that window a consumer running tls_handshake_cancel() followed by sockfd_put() (svc_sock_free) or __fput_sync() (xs_reset_transport) releases sock->file. sock_release() then runs sock_orphan(), zeroing sk_socket, and frees the struct socket. The accept-side code either reads NULL through sk_socket or chases freed memory. The submit-side sock_hold() does not prevent this. sk_refcnt protects struct sock, but struct socket and sock->file are independently refcounted via the file descriptor the consumer owns. Pinning sk leaves sock and sock->file unprotected. Retarget the accept-side dereferences at req->hr_file, which was pinned at submit time, instead of req->hr_sk->sk_socket->file. Pinning on its own is not sufficient: a consumer that cancels between handshake_req_next() returning and accept_doit reaching FD_PREPARE() takes the !remove_pending() branch in handshake_req_cancel() and drops hr_file before the accept side takes its own reference. Hand off an additional file reference inside handshake_req_next(), under hn_lock, so the accept side operates on a reference that no concurrent handshake_req_cancel() can revoke. FD_PREPARE() consumes that handed-off reference, either by transferring it to the new fd in fd_publish() or by dropping it in the cleanup destructor on error; the explicit get_file() that previously balanced FD_PREPARE() is therefore redundant and goes away. Update handshake_req_cancel_test2 and _test3 to simulate the FD_PREPARE() consumption with an fput() so the kunit file-count assertions stay balanced.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidenceUse-after-free race condition in Linux kernel's net/handshake subsystem where the accept-side code dereferences sock->file after the submit-side consumer releases it via tls_handshake_cancel() followed by sockfd_put() or __fput_sync(). The race window exists between handshake_req_next() dropping hn_lock and accept_doit reading the socket, allowing sock_release() to free struct socket before the accept path accesses it.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- Low
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Identify kernel versionRun 'uname -r' or 'cat /proc/version' to obtain the running kernel versionAffected if The kernel version is older than the patched version containing the fix for this race condition
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Verify net/handshake module presenceCheck if the kernel has the net/handshake module or code by looking for /proc/net/handshake or examining kernel config for CONFIG_HANDSHAKE (if accessible)Affected if The net/handshake functionality is present in the kernel and the version is unpatched
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Identify TLS accept operationsReview running services that perform TLS accept operations (e.g., web servers, VPN services, database servers with TLS) using commands like 'ss -tlnp' or 'netstat -tlnp' to list listening TLS socketsAffected if The system is accepting TLS connections, which triggers the vulnerable handshake accept code path
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Check for concurrent TLS cancel activityMonitor for processes calling tls_handshake_cancel() concurrently with accept operations; this requires kernel tracing (e.g., ftrace, eBPF) if active exploitation is suspectedAffected if Concurrent tls_handshake_cancel() calls occur while TLS accept is in progress, creating the race window
The system is affected if it runs a kernel version older than the patched version, has the net/handshake module present, and accepts TLS connections which triggers the vulnerable accept processing path.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
dbcve · scopedApply the kernel patch that retargets accept-side dereferences at the pre-pinned req->hr_file and hands off an additional file reference under hn_lock to prevent concurrent cancellation from revoking the reference.
Linux kernel version containing the fix commit (any stable/longterm kernel release dated after the patch was merged into the upstream kernel tree)
- Identify the current running Linux kernel version using `uname -r`
- Check if your distribution has released a kernel update that includes the fix for CVE-2026-63979
- For enterprise distributions (RHEL, Ubuntu LTS, Debian, SUSE), apply the vendor-provided kernel security update
- Reboot the system to load the patched kernel
- Verify the fix is applied by checking the kernel version matches a release after the patch date
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation4.0 h
- Implementation8.0 h
- Testing12.0 h
- Review / QA6.0 h
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Free · runs locallyCheck whether your project pulls in CVE-2026-63979 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2026-63979 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Version or environment caveats, and links to real fixes
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