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VulnerabilityAwaiting classification

CVE-2026-64523

CRITICAL · 9.8 CVSS v3.1 Published 2026-07-25
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
100/100
Remediation priority · Urgent
Remotely reachable No privileges Zero-click 4 weeks old

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 · unedited
In the Linux kernel, the following vulnerability has been resolved: net/handshake: Take a long-lived file reference at submit handshake_nl_accept_doit() needs the file pointer backing req->hr_sk->sk_socket to survive the window between handshake_req_next() and the subsequent FD_PREPARE() and get_file(). The submit-side sock_hold() does not provide that. sk_refcnt keeps struct sock alive, but struct socket is owned by sock->file: when the consumer fputs the last file reference, sock_release() tears the socket down regardless of any sock_hold. Add an hr_file pointer to struct handshake_req and acquire an explicit reference on sock->file during handshake_req_submit(). handshake_complete() and handshake_req_cancel() release the reference on the completion-bit-winning path. The submit error path must also release the file reference, but after rhashtable insertion a concurrent handshake_req_cancel() can discover the request and race the error path. Gate the error-path cleanup -- sk_destruct restoration, fput, and request destruction -- with test_and_set_bit(HANDSHAKE_F_REQ_COMPLETED), the same serialization handshake_complete() and handshake_req_cancel() already use. When cancel has already claimed ownership, the submit error path returns without touching the request; socket teardown handles final destruction. The accept-side dereferences are not yet retargeted; that change comes in the next patch.

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 confidence

Race condition in Linux kernel's net/handshake subsystem where file reference counting is insufficient. The submit-side sock_hold() keeps struct sock alive but struct socket is owned by sock->file; when the consumer fputs the last file reference, sock_release() tears down the socket regardless of sock_hold, leading to use-after-free. The fix adds an hr_file pointer to struct handshake_req with explicit reference acquisition on sock->file.

MitigationApply the kernel patch that adds hr_file pointer and proper file reference counting in handshake_req_submit(), handshake_complete(), and handshake_req_cancel() to prevent the race condition.

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 checks

Work through these to decide whether this CVE applies to you.

  1. Check kernel version for patch presence
    Run 'uname -r' or check /proc/version. Compare against the version that includes the fix for this race condition (the fix adds hr_file pointer handling to struct handshake_req).
    Affected if Kernel version is older than the patched version containing the race condition fix for net/handshake.
  2. Verify net/handshake module is present
    Check if the kernel has handshake support: 'ls //net/handshake' or look for 'handshake' in kernel config via 'zcat /proc/config.gz 2>/dev/null | grep -i handshake' or check /boot/config-$(uname -r).
    Affected if The net/handshake module or code exists in the kernel, making the code path potentially reachable.
  3. Determine if TLS handshake operations are in use
    Check for active TLS sockets using 'ss -M' or examine /proc/net/sockstat for TLS activity. The race occurs during handshake request processing on sockets accepting TLS connections.
    Affected if The system accepts or processes TLS connections, which triggers the net/handshake code path.
  4. Look for the specific vulnerable code pattern
    If kernel source is available, grep for 'handshake_req_next' and check if FD_PREPARE/get_file is called without proper file reference acquisition between request iteration and file preparation.
    Affected if The code lacks the hr_file pointer and proper test_and_set_bit(HANDSHAKE_F_REQ_COMPLETED) serialization present in the patched version.

You are affected if your kernel version predates the fix and the system processes TLS connections using the net/handshake module.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

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.

From vendor data
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Apply the kernel patch that adds hr_file pointer and proper file reference counting in handshake_req_submit(), handshake_complete(), and handshake_req_cancel() to prevent the race condition.

Have this fixed Scoped from the published advisory
  • Consultation2.0 h
  • Implementation12.0 h
  • Testing8.0 h
  • Review / QA4.0 h
26.0 hours of engineering $4,480
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-64523 in production — separate from our analysis above.

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What this is

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What belongs here
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  • Version or environment caveats, and links to real fixes
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