CVE-2026-18746: NULL pointer dereference in Zephyr LwM2M client when the CoAP Block1 context pool is exhausted
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: 0.26% (FIRST EPSS).
- Anyone who can reach it over the internet 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
parse_write_op() in subsys/net/lib/lwm2m/lwm2m_message_handling.c handles inbound CoAP WRITE/CREATE requests that carry a Block1 option. For the first block of a transfer it called init_block_ctx() and then immediately stored the peer-selected block size with block_ctx->ctx.block_size = block_size before inspecting the return code. init_block_ctx() sets the caller's pointer to NULL and returns -ENOMEM when no entry of the static block1_contexts[] pool is free or timed out, so that store dereferences a NULL pointer. The pool holds CONFIG_LWM2M_NUM_BLOCK1_CONTEXT entries (default 3) and an entry is only reclaimed once its transfer completes, fails, or ages past 30 seconds. A peer that reaches the client's LwM2M socket can therefore start three block-wise writes on three distinct object paths with the CoAP More bit set and leave them incomplete, then send the first block of a fourth write on a new path to reach the unguarded dereference. Reachability is gated only by the connected UDP socket's source-address filter unless CONFIG_LWM2M_DTLS_SUPPORT is enabled — which has no default — so in a NoSec deployment an on-path or address-spoofing attacker needs no credentials; the same sequence is also reachable from a bootstrap or lower-trust server, and can be hit accidentally by a legitimate server running four concurrent block transfers. The write targets a fixed low address with a value between 0 and 7, so the consequence is a fatal memory fault (BusFault or corrupted low memory leading to a fault) rather than a usable memory-corruption primitive: the device crashes or resets. Confidentiality and integrity are not affected. The fix moves the store below the guard and validates the context pointer itself instead of the return code, so the context is only touched once it is known to be valid.
- Published
- Sep 29, 2026
- Updated
- Nov 6, 2026
- EPSS
- 0.2% · 18th percentile
- CWE
- CWE-476
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 · 0.2%
CISA SSVC decision
- Exploitation
- none
- Automatable
- no
- Technical impact
- partial
Vulnrichment: CISA's decision-tree inputs.
CNA vs NVD score
- NVD
- 5.9
- CNA · zephyr
- 5.9
- agree
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.
| Vendor | Product | CPE |
|---|---|---|
| zephyrproject | zephyr | cpe:2.3:o:zephyrproject:zephyr |
Affected versions
NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.
- zephyrproject zephyr3.7.0 and later · before 4.3.2
- zephyrproject zephyr4.4.0 and later · before 4.5.0
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
- 3.7.0 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-2026-18416Sep 28, 2026 · Out-of-bounds read in CoAP well-known-core Uri-Query href matching (match_path_uri)21Monitor
- ← EarlierCVE-2026-18417Sep 29, 2026 · Wild pointer dereference in Zephyr BSD sockets when a TCP listening socket reports an asynchronous error26Monitor
- Later →CVE-2026-18747Sep 29, 2026 · Integer underflow of net_buf length in the MCUmgr serial (SMP over console) transport leads to out-of-bounds read24Monitor
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 recordedsame day
- TodayNov 10, 2026+42 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-2026-1067870 days apartNULL-pointer / out-of-bounds write in Zephyr MCTP I2C+GPIO target binding driven by an unauthenticated I2C controller32Monitor
- CVE-2026-1589116 days apartNULL pointer dereference in Zephyr MQTT-SN client when removing a non-responsive gateway30Monitor
- CVE-2026-8704538 days apartNULL pointer dereference in the Zephyr HTTP/2 server when a header block is completed by a CONTINUATION frame30Monitor
- CVE-2026-1181050 days apartNULL-pointer dereference in UpdateHub OTA agent on empty inner metadata array (remote DoS)30Monitor
- CVE-2026-7997622 days apartNULL pointer dereference in the MCTP I2C+GPIO target binding triggerable by a peer I2C controller28Monitor
- CVE-2026-8238927 days apartBluetooth Classic HFP AG wipes an object still linked in the SDP request list on connect failure, causing a NULL dereference26Monitor
Chain candidates
An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.
—
Bug bounty scope
No known public program.
Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).
Technical details
Attack conditions
- Anyone who can reach it over the internet 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
- none
- Availability
- high · the service can be disrupted
- Attack vector
- Network
- Attack complexity
- High
- Privileges required
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality impact
- None
- Integrity impact
- None
- Availability impact
- High
Weakness class (CWE)
CWE-476 · NULL Pointer DereferenceCVSS vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
nvd-primary
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
- SSVC exploitation— → none
- Exploit maturity— → none
- Fix✗ → ✓
For records you follow, these changes also arrive as notifications. →
References
Vendor advisories and official records. Exploit/PoC links are deliberately left out.