# CVE-2026-64127: Bluetooth: L2CAP: ecred_reconfigure: send packed pdu, not stack pointer

> A Bluetooth L2CAP vulnerability leaks kernel stack addresses to remote peers due to incorrect PDU size and pointer usage, requiring a kernel patch.

- **Severity:** Medium 5.5 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 19 Jul 2026
- **Updated:** 19 Jul 2026
- **Also known as:** BELL-CVE-2026-64127, DEBIAN-CVE-2026-64127, GHSA-w532-m3j8-f99h, UBUNTU-CVE-2026-64127

## What is CVE-2026-64127?

CVE-2026-64127 is a medium-severity vulnerability in Linux kernel, published on 19 Jul 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

In the Linux kernel, the following vulnerability has been resolved:

Bluetooth: L2CAP: ecred_reconfigure: send packed pdu, not stack pointer

Commit 1c08108f3014 ("Bluetooth: L2CAP: Avoid -Wflex-array-member-not-at-end
warnings") converted the on-stack request PDU in l2cap_ecred_reconfigure()
from an explicit packed struct to DEFINE_RAW_FLEX(), but did not adjust the
size and source-pointer arguments to l2cap_send_cmd():

  -    struct {
  -            struct l2cap_ecred_reconf_req req;
  -            __le16 scid;
  -    } pdu;
  +    DEFINE_RAW_FLEX(struct l2cap_ecred_reconf_req, pdu, scid, 1);
       ...
       l2cap_send_cmd(conn, chan->ident, L2CAP_ECRED_RECONF_REQ,
                      sizeof(pdu), &pdu);

After the conversion, DEFINE_RAW_FLEX() expands to declare an anonymous
union pdu_u plus a local pointer "pdu" pointing at it. Therefore:

  - sizeof(pdu) is now sizeof(struct l2cap_ecred_reconf_req *) = 8 on
    64-bit (4 on 32-bit), not the 6 bytes of (mtu, mps, scid[1]).
  - &pdu is the address of the local pointer's stack storage, not the
    address of the request payload.

l2cap_send_cmd() forwards (data, count) to l2cap_build_cmd(), which calls
skb_put_data(skb, data, count). The L2CAP_ECRED_RECONFIGURE_REQ packet
body therefore contains 8 bytes copied from the kernel stack starting at
&pdu -- the 8 bytes overlap the pdu pointer's value, leaking a kernel
stack address to the paired Bluetooth peer. The intended (mtu, mps, scid)
fields are not transmitted at all, so the peer rejects the request as
malformed and the L2CAP_ECRED_RECONFIGURE feature itself has been broken
for the local-side initiator since the introducing commit landed.

The sibling site l2cap_ecred_conn_req() in the same commit was converted
correctly (sizeof(*pdu) + len, pdu); only this site was missed.

Restore the original semantics: pass the full flex-struct size via
struct_size(pdu, scid, 1) and the pdu pointer (the struct address) as
the source.

Validated on a stock 7.0-based host kernel via the real call path:
setsockopt(SOL_BLUETOOTH, BT_RCVMTU, ...) on a BT_CONNECTED
L2CAP_MODE_EXT_FLOWCTL socket emits an L2CAP_ECRED_RECONFIGURE_REQ
whose body is 8 bytes (the on-stack pdu local's value) rather than
the expected 6. Three captures from fresh socket / fresh hciemu peer
on the same host -- low bytes vary per call, high 0xffff confirms a
kernel virtual address (KASLR-randomised stack slot, not a fixed
string):

  RECONF_REQ body (ident=0x02 len=8): 42 fb 54 af 0e ca ff ff
  RECONF_REQ body (ident=0x02 len=8): 52 3d 2e af 0e ca ff ff
  RECONF_REQ body (ident=0x02 len=8): b2 fc 5b af 0e ca ff ff

After this patch the body is 6 bytes carrying the expected
little-endian (mtu, mps, scid).

## Which versions are affected by CVE-2026-64127?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-64127?

Apply the vendor's patch.

## Is CVE-2026-64127 being exploited?

There is no known exploitation of CVE-2026-64127 in the wild and no public exploit code.

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-64127 and fix it if it is affected.

What it is: CVE-2026-64127 is a medium-severity vulnerability in Linux kernel, published on 19 Jul 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-64127 in the wild and no public exploit code.

Affected product: Linux kernel. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-64127/ (Markdown: https://insights.sbomify.com/CVE-2026-64127/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-64127
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-64127
- OSV: https://osv.dev/vulnerability/CVE-2026-64127

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-64127/
Summaries are generated and may contain mistakes; the official description above is the record.