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VulnerabilityAwaiting classification

CVE-2025-68775

CRITICAL · 9.8 CVSS v3.1 Published 2026-01-13
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

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: duplicate handshake cancellations leak socket When a handshake request is cancelled it is removed from the handshake_net->hn_requests list, but it is still present in the handshake_rhashtbl until it is destroyed. If a second cancellation request arrives for the same handshake request, then remove_pending() will return false... and assuming HANDSHAKE_F_REQ_COMPLETED isn't set in req->hr_flags, we'll continue processing through the out_true label, where we put another reference on the sock and a refcount underflow occurs. This can happen for example if a handshake times out - particularly if the SUNRPC client sends the AUTH_TLS probe to the server but doesn't follow it up with the ClientHello due to a problem with tlshd. When the timeout is hit on the server, the server will send a FIN, which triggers a cancellation request via xs_reset_transport(). When the timeout is hit on the client, another cancellation request happens via xs_tls_handshake_sync(). Add a test_and_set_bit(HANDSHAKE_F_REQ_COMPLETED) in the pending cancel path so duplicate cancels can be detected.

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

A race condition in the Linux kernel's net/handshake module allows duplicate cancellation requests to trigger a reference count underflow. When a handshake request is cancelled, it's removed from the pending list but remains in the hash table. A second cancellation attempt (e.g., from server FIN after timeout followed by client timeout) calls remove_pending() which returns false, then incorrectly adds another sock reference, causing refcount underflow and potential use-after-free.

MitigationApply the upstream kernel patch that adds test_and_set_bit(HANDSHAKE_F_REQ_COMPLETED) in the pending cancel path to detect and reject duplicate cancellation requests.

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. Identify kernel version
    Run 'uname -r' or check /proc/version to determine the running kernel version
    Affected if The kernel version is older than the version that includes the fix for CVE-2025-68775 (the patch adding test_and_set_bit(HANDSHAKE_F_REQ_COMPLETED) in the pending cancel path)
  2. Determine if net/handshake is enabled
    Check if the kernel was built with CONFIG_HANDSHAKE (look in /boot/config-* or /proc/config.gz, or check for /proc/net/handshake* existence)
    Affected if The net/handshake module or functionality is compiled into the running kernel (the vulnerability only applies when handshake support exists)
  3. Verify fix presence in kernel source
    If kernel source is available, grep for 'test_and_set_bit.*HANDSHAKE_F_REQ_COMPLETED' in net/handshake/*.c files, or check the pending cancel function for the duplicate request guard
    Affected if The fix code is absent; duplicate cancellation requests are not being rejected before triggering the refcount underflow
  4. Check for active handshake sockets
    Inspect /proc/net/handshake* (if it exists) or use 'ss -x' to look for handshake-associated sockets
    Affected if There are active handshake sockets in the system (the race condition requires an existing handshake to cancel twice)

A system is affected if it runs a kernel older than the fixed version, has net/handshake enabled, and uses handshake functionality where duplicate cancellation requests can occur.

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 upstream kernel patch that adds test_and_set_bit(HANDSHAKE_F_REQ_COMPLETED) in the pending cancel path to detect and reject duplicate cancellation requests.

Have this fixed Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing8.0 h
  • Review / QA4.0 h
18.0 hours of engineering $3,040
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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-2025-68775 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
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