CVE-2026-19938: Use-after-free of an ATT PDU buffer when signing an outgoing Bluetooth ATT Signed Write Command fails
Noroxi assessment
Priority: Monitor (action score 23/100)
- The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
- Probability of exploitation in the next 30 days: 0.16% (FIRST EPSS).
- Someone on the same network segment can trigger it. No account or password is required. No user action is required. Special conditions such as timing or configuration are required.
- Fixed version: zephyrproject zephyr 4.3.2, 4.5.0.
Low priority for now. Upgrade to zephyrproject zephyr 4.3.2, 4.5.0 or later.
Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it
Primary sources: NVD · CVE.org · FIRST EPSS
The Bluetooth host's ATT transmit path releases a buffer it does not own when signing fails. chan_send() in subsys/bluetooth/host/att.c documents (and every other error exit implements) the contract that on failure the caller retains ownership of the net_buf; the BT_ATT_OP_SIGNED_WRITE_CMD branch instead called net_buf_unref(buf) when bt_smp_sign() returned an error and then returned that error to the caller. The callers act on the contract: process_queue() re-queues the buffer with k_queue_prepend(), bt_att_chan_send_rsp() puts it back on chan->tx_queue, bt_att_chan_req_send() restores it into the request, and att_req_retry() unreferences it — so the already-freed buffer was re-queued, later dereferenced, and eventually freed again. An ATT Signed Write Command is produced when an application calls bt_gatt_write_without_response_cb() with sign set on an unencrypted connection. bt_smp_sign() fails whenever no local CSRK exists for the peer (-ENOENT), and whether one exists is negotiated with the peer: smp_distribute_keys() stores a local CSRK only when the peer's pairing key-distribution field requests the signing key and bonding was agreed. A peer can therefore pair without accepting the CSRK, pair with No Bonding, remain unpaired, or keep the link unencrypted, and the victim's next signed write takes the failing path. Because struct net_buf's node field is simultaneously the linkage word for the ATT TX FIFO, for the deferred-destroy list used by the att_pool destroy callback att_tx_destroy(), and for the pool free list, the mishandled buffer corrupts these lists and can be re-issued by bt_att_create_pdu() to a new PDU while the ATT TX path still holds it. The same branch also saved the net_buf_simple_state only after signing, so a buffer restored after a bt_l2cap_send_pdu() failure kept its 12-octet signature; a subsequent retry re-signed it and appended a second signature with net_buf_add(buf, 12) to a buffer that bt_att_create_pdu() sized for exactly one, writing past the end of the pooled buffer in builds where the net_buf tailroom assertion is compiled out. Impact is host-side memory corruption in the Bluetooth stack: list corruption, a pooled ATT buffer with two owners (wrong PDU contents transmitted, or a double free when the queues are drained at disconnect), and a bounded out-of-bounds write on the retry path — typically observed as a crash or assertion failure. Exposure requires the deprecated CONFIG_BT_SIGNING to be enabled and an application that actually issues signed writes; in that configuration the triggering condition is under the remote peer's control.
- Published
- Oct 13, 2026
- Updated
- Nov 4, 2026
- EPSS
- 0.1% · 5th percentile
- CWE
- CWE-416
Report tools
Action score
23
Monitor
Low priority for now.
- CVSS
- 23 / 40 · 5.9 / 10
- CISA KEV
- 0 / 30 · Not listed
- EPSS
- 0 / 30 · 0.1%
CISA SSVC decision
- Exploitation
- none
- Automatable
- no
- Technical impact
- partial
Vulnrichment: CISA's decision-tree inputs.
CNA vs NVD score
- NVD
- —
- CNA · zephyr
- 5.9
- NVD has not scored this yet; the score shown is the CNA’s.
The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.
Get told when this record changes
- Not in KEV: no record of exploitation in the wild
- No public exploit code on record
- A fix has been released
If any of these changes, we'll tell you in the daily email digest.
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Noroxi analysis
What does it mean in your environment?
The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.
We use this product, ask for helpAffected systems
Is your version affected?
Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.
—
Versions reported by the vendor
Affected version ranges reported by the assigning authority (zephyr). Independent of NVD's CPE analysis and usually ahead of it.
zephyrproject zephyr
- 2.3.0 and later · before 4.3.2affected · semver
- 4.4.0 and later · before 4.5.0affected · semver
Same product
zephyrproject: all recordsOther highest-scoring records for the same primary product.
- CVE-2023-4260Potential off-by-one buffer overflow vulnerability in the Zephyr FS subsystem40Plan
- CVE-2021-3625Buffer overflow in Zephyr USB DFU DNLOAD40Plan
- CVE-2020-10071Insufficient publish message length validation in MQTT40Plan
Published before and after this one in the same product
- ← EarlierCVE-2026-19936Oct 13, 2026 · Bluetooth Mesh delayable message queue: unsynchronized list access leads to NULL pointer dereference19Monitor
- ← EarlierCVE-2026-19937Oct 13, 2026 · Bluetooth Mesh Access layer permanently leaks delayable-message contexts, disabling all model responses22Monitor
- Later →CVE-2026-19939Oct 13, 2026 · Bluetooth Classic AVDTP: stale timeout work on signalling-channel disconnect leads to kernel timeout-list corruption25Monitor
Remediation
Which version to upgrade to
Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.
| Product / package | Fixed version | Source |
|---|---|---|
| zephyrproject zephyr | 4.3.2 | Vendor (CNA) |
| zephyrproject zephyr | 4.5.0 | Vendor (CNA) |
Exploit status
No known public exploit
No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.
Research context
For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.
Timeline
From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.
- Published
- Fix recorded+2 d
- TodayNov 6, 2026+24 d
FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).
Patch and commit links
Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.
Credits
All researchersFinders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.
No credits in the CNA record.
Variant candidates
Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.
- CVE-2026-8503521 days apartUse-after-free via dynamically allocated message queue retained by the CAN RX filter35Monitor
- CVE-2026-1236660 days apartUse-after-free freeing an armed dynamically-allocated k_timer in Zephyr userspace object disposal35Monitor
- CVE-2026-7997910 days apartStale TLB entries after demand-paging page-out let arm64 user threads access reused physical frames31Monitor
- CVE-2026-1066793 days apartSMP use-after-free in Zephyr `CONFIG_USERSPACE` dynamic kernel-object tracking, reachable from unprivileged user threads31Monitor
- CVE-2026-199352 days apartUse-after-free of an L2CAP CoC channel object in the Zephyr Bluetooth host: RX work item is not cancelled on channel teardown30Monitor
- CVE-2026-1068574 days apartUse-after-free of GATT subscribe params in Bluetooth host CCC-write response handler30Monitor
Chain candidates
An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.
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Bug bounty scope
No known public program.
Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).
Technical details
Attack conditions
- Someone on the same network segment can trigger it.
- No account or password is required.
- No user action is required.
- Special conditions such as timing or configuration are required.
If successful
- Confidentiality
- none
- Integrity
- low · data or configuration can be modified
- Availability
- high · the service can be disrupted
- Attack vector
- Adjacent
- Attack complexity
- High
- Privileges required
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality impact
- None
- Integrity impact
- Low
- Availability impact
- High
Weakness class (CWE)
CWE-416 · Use After FreeCVSS vector
CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:H
nvd-secondary
Root cause
After a memory region is freed, another reference pointing to it is still used. By then, the same region may have been allocated for different data.
The bug in code
The whole CWE-416 classA representative example of this vulnerability class. Not the vendor's source code; it shows the faulty pattern and its fix.
Vulnerable
free(dev->buf);
/* ... another thread is still running ... */
process(dev->buf);Fixed
lock(&dev->lock);
free(dev->buf);
dev->buf = NULL;
unlock(&dev->lock);Attack context
MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.
MITRE has no CAPEC/ATT&CK mapping for this CWE.
Change log
- Fix✗ → ✓
- SSVC exploitation— → none
- Exploit maturity— → none
For records you follow, these changes also arrive as notifications. →
References
Show all references (1 more)Show less
Vendor advisories and official records. Exploit/PoC links are deliberately left out.