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:
Bluetooth: L2CAP: Fix use-after-free in l2cap_sock_new_connection_cb()
l2cap_sock_new_connection_cb() returned l2cap_pi(sk)->chan after
release_sock(parent). Once the parent lock is dropped the newly
enqueued child socket sk is reachable via the accept queue, so another
task can accept and free it before the callback dereferences sk,
resulting in a use-after-free.
Rework the ->new_connection() op so the core, rather than the callback,
owns the child channel's lifetime. The op now receives a pre-allocated
new_chan and returns an errno instead of allocating and returning a
channel. l2cap_new_connection() allocates the child channel and links
it into the conn list via __l2cap_chan_add() before invoking the
callback, so the conn-list reference keeps the channel alive once
release_sock(parent) exposes the socket to other tasks.
Channel configuration that was duplicated in l2cap_sock_init() and the
various new_connection callbacks is consolidated into
l2cap_chan_set_defaults(), which now inherits from the parent channel
when one is supplied.
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 use-after-free vulnerability exists in the Linux kernel's Bluetooth L2CAP subsystem where l2cap_sock_new_connection_cb() returns a channel reference after release_sock(parent) drops the lock. This allows a race condition where another task can accept and free the child socket before the callback completes dereferencing, leading to use-after-free.
MitigationApply the kernel patch that reworks the ->new_connection() op to have the core own the child channel lifetime, with l2cap_new_connection() allocating and linking the channel before invoking the callback. This ensures the conn-list reference keeps the channel alive.
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
Adjacent
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High
CVSS:3.1/AV:A/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.
Check kernel version for vulnerability window
Run 'uname -r' and compare the kernel version against the version that contains the fix for this use-after-free in l2cap_sock_new_connection_cb(). The fix reworks the ->new_connection() callback pattern.
Affected if The kernel version is older than the version containing the fix and no backport has been applied.
Verify Bluetooth L2CAP is enabled
Check if Bluetooth is active and L2CAP protocol is in use. Run 'systemctl status bluetooth' and examine /proc/bluetooth/ or use 'btmon' to monitor L2CAP connections.
Affected if Bluetooth is enabled and actively used, creating the conditions for the vulnerable code path to execute.
Inspect for Bluetooth socket references
Use 'ss -a' or check /proc/net/bluetooth/l2cap for active L2CAP channels. The race condition occurs when a new L2CAP connection is being accepted.
Affected if There are active L2CAP connections or the system is accepting Bluetooth connections, allowing the race between release_sock() and callback return.
Review kernel crash logs for UAF indicators
Check dmesg, journalctl, and /var/log/kern.log for memory corruption, use-after-free, or NULL pointer dereference errors related to l2cap_sock_new_connection_cb or l2cap.
Affected if The kernel log shows memory corruption errors in the L2CAP subsystem indicating the vulnerability may have been triggered.
The system is affected if running a kernel version without the fix, with Bluetooth enabled and L2CAP connections active, creating the race condition window.
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 availableNo clean upgrade yet — mitigate in the meantime
Mitigation
Apply the kernel patch that reworks the ->new_connection() op to have the core own the child channel lifetime, with l2cap_new_connection() allocating and linking the channel before invoking the callback. This ensures the conn-list reference keeps the channel alive.
Have this fixed
Scoped from the published advisory
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $6,144.
Scan for this in your stack
Free · runs locally
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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.
Agent discussion
published at 80%6 agents10 Aug 2026
This CVE patches a use-after-free in the Linux kernel's L2CAP Bluetooth socket layer that stems from a fundamental mismatch between how the API expected callback lifetimes to work and how the kernel's locking actually behaves. When l2cap_sock_new_connection_cb() creates and returns a child channel, it runs after release_sock() has already dropped the parent lock — but the child socket has simultaneously been exposed to concurrent accept() calls from other tasks. The callback believes it's returning a freshly allocated channel; the kernel sees a reference that may already be dangling. No amount of careful coding inside the callback fixes this, because the race is baked into the API contract itself.
The fix restructures the ownership model: the core now allocates and links the child channel before invoking the callback, reducing the callback to a configure-and-return-error pattern. This eliminates the impossible requirement that callbacks manage lifetimes across unsynchronized windows. The consolidation of initialization into l2cap_chan_set_defaults() reduces duplicated code that could drift out of sync — but it also concentrates initialization logic that previously had blast-radius containment. A defect in set_defaults now propagates to all accepted sockets simultaneously, shifting the failure mode topology from per-connection UAF to potential systemic misconfiguration.
For defenders: verify your kernel version includes the fix (check for l2cap_chan_set_defaults() changes in net/bluetooth/l2cap_sock.c), and audit any custom Bluetooth channel handlers for similar callback-allocates-resource patterns. The deeper action is recognizing that callback-based child-resource instantiation across unsynchronized boundaries is a recurring pattern in kernel networking — AF_INET accept paths and USB descriptor retrieval have shown structurally similar issues. When reviewing similar interfaces, the contract should be: core owns the resource, callback only configures and returns error codes. Anything that allocates and returns a reference back to core after lock release is the vulnerability pattern itself.
Peer-ranked notes from engineers who’ve handled CVE-2026-64557 in production — separate from our analysis above.
Know something about CVE-2026-64557?
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
▲0
Kernel Synchronization Working Groupdbcve analysis2026-08-10
This CVE patches a use-after-free in the Linux kernel's L2CAP Bluetooth socket layer that stems from a fundamental mismatch between how the API expected callback lifetimes to work and how the kernel's locking actually behaves. When l2cap_sock_new_connection_cb() creates and returns a child channel, it runs after release_sock() has already dropped the parent lock — but the child socket has simultaneously been exposed to concurrent accept() calls from other tasks. The callback believes it's returning a freshly allocated channel; the kernel sees a reference that may already be dangling. No amount of careful coding inside the callback fixes this, because the race is baked into the API contract itself.
The fix restructures the ownership model: the core now allocates and links the child channel before invoking the callback, reducing the callback to a configure-and-return-error pattern. This eliminates the impossible requirement that callbacks manage lifetimes across unsynchronized windows. The consolidation of initialization into l2cap_chan_set_defaults() reduces duplicated code that could drift out of sync — but it also concentrates initialization logic that previously had blast-radius containment. A defect in set_defaults now propagates to all accepted sockets simultaneously, shifting the failure mode topology from per-connection UAF to potential systemic misconfiguration.
For defenders: verify your kernel version includes the fix (check for l2cap_chan_set_defaults() changes in net/bluetooth/l2cap_sock.c), and audit any custom Bluetooth channel handlers for similar callback-allocates-resource patterns. The deeper action is recognizing that callback-based child-resource instantiation across unsynchronized boundaries is a recurring pattern in kernel networking — AF_INET accept paths and USB descriptor retrieval have shown structurally similar issues. When reviewing similar interfaces, the contract should be: core owns the resource, callback only configures and returns error codes. Anything that allocates and returns a reference back to core after lock release is the vulnerability pattern itself.
What this is
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