Medium

CVE-2026-53208 — Bluetooth: L2CAP: reject BR/EDR signaling packets over MTUsig

In the Linux kernel, the following vulnerability has been resolved: Bluetooth: L2CAP: reject BR/EDR signaling packets over MTUsig net/bluetooth/l2cap_core.c:l2cap_sig_channel() accepts BR/EDR signaling packets up to the channel MTU and dispatches each command without enforcing the signaling MTU (MTUsig). A Bluetooth BR/EDR peer within radio range can send a fixed-channel CID 0x0001 packet that is larger than MTUsig and contains many L2CAP_ECHO_REQ commands before pairing. In a real-radio stock-kernel run, one 681-byte signaling packet containing 168 zero-length ECHO_REQ commands made the target transmit 168 ECHO_RSP frames over about 220 ms. Impact: a Bluetooth BR/EDR peer within radio range, before pairing, can force 168 ECHO_RSP frames from one 681-byte fixed-channel signaling packet containing packed ECHO_REQ commands. Define Linux's BR/EDR signaling MTU as the spec minimum of 48 bytes and reject any larger signaling packet with one L2CAP_COMMAND_REJECT_RSP carrying L2CAP_REJ_MTU_EXCEEDED before any command is dispatched. The Bluetooth Core spec wording for MTUExceeded says the reject identifier shall match the first request command in the packet, and that packets containing only responses shall be silently discarded. Linux intentionally deviates from that prescription: silently discarding desynchronizes the peer because the remote stack never learns its responses were dropped, and locating the first request command requires walking command headers past MTUsig, i.e. processing bytes from a packet we have already decided is too large to process. We therefore always emit one reject and use the identifier from the first command header, a single fixed-offset byte read. The unrestricted BR/EDR signaling parser and ECHO_REQ response path both trace to the initial git import; no later introducing commit is available for a Fixes tag.

Published Jun 25, 2026 · Updated Oct 15, 2026 · Sources: NIST National Vulnerability Database, CVE Program (cve.org) e CISA ADP, GitHub Security Advisories · CNA: Linux

Low

Who exploits it and how urgent it is

A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.

No exploitation signal in the sources consulted so far.

How the score was calculated

EPSS 0.1% (30-day exploitation probability)+0
Technical severity (medium)+3

The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.

Exploitation

Not confirmed

Not in CISA KEV — an absence of record, not proof it is unexploited.

EPSS FIRST

0.12%

ahead of 2% of scored CVEs · Oct 14, 2026

Affects

Linux

Linux and 1 more

CVSS base

5.5

Medium · 2 source(s)

Remediation

Fixes and mitigations documented by the sources — linked to the original advisory.

Documented patch — git.kernel.org (NIST National Vulnerability Database)
Documented patch — git.kernel.org (NIST National Vulnerability Database)
Documented patch — git.kernel.org (NIST National Vulnerability Database)
Documented patch — git.kernel.org (NIST National Vulnerability Database)
Documented patch — git.kernel.org (NIST National Vulnerability Database)
Documented patch — git.kernel.org (NIST National Vulnerability Database)
Documented patch — git.kernel.org (NIST National Vulnerability Database)
Documented patch — git.kernel.org (NIST National Vulnerability Database)

First 24 hours

Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.

Identify exposed assets running the affected vendor/product/version combinations (Linux Linux, Linux Linux Kernel).
Apply the fixed version or the patch documented under Remediation.
Search available logs for exploit probes, errors and authentication anomalies.

Affected scope

Vendor, product and versions as the sources word them.

Vendor	Product	Versions	Status	Source
Linux	Linux	version 2.6.12≥ 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and < dd214733544427587a95f66dbf3adff072568990≥ 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and < e2b8acf9405bd9b1baf1c54dc897b0905db689bf≥ 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and < dedc92b96dc1d8919a3bdf2495ede68922ef7ebc≥ 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and < a8335f3db15bd1e0e82e0db5d488fabc7d10d1ab≥ 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and < 214a2042b16b3c8d798a8b9ef9f36094f13a9859≥ 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and < b20e8a98dd29b121f58fcdf51e8576119aba536a≥ 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and < fa5823126239b3e453fac1a2fe50726c7f4a55e1 and 1 more ≥ 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and < e05c4ac575b457978a7ef441053394169084869c	Vulnerable	CVE Program (cve.org) e CISA ADP
Linux	Linux Kernel	version 7.1-rc2version 7.1-rc6version 7.1-rc5version 7.1-rc4version 7.1-rc3≥ 2.6.12.1 and < 5.10.259version 7.1-rc1version 2.6.12-rc5 and 10 more version 2.6.12-rc4version 2.6.12-rc3version 2.6.12-rc2version 2.6.12≥ 6.19 and < 7.0.13≥ 6.13 and < 6.18.36≥ 6.7 and < 6.12.94≥ 6.2 and < 6.6.143≥ 5.16 and < 6.1.176≥ 5.11 and < 5.15.210	Vulnerable	NIST National Vulnerability Database

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

Attack vector

Local

Attack complexity

Low

Privileges required

Low

User interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

None

Availability

High

Every base score collected

Sources score independently and may disagree; each row says who scored it and under which version.

Score	Version	Severity	Expl.	Impact	Scored by
5.5	CVSS 3.1	Medium	1.8	3.6	nvd@nist.gov via NIST National Vulnerability Database
5.5	CVSS 3.1	Medium	—	—	GitHub, Inc. via GitHub Security Advisories

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H (score shown at the top: nvd@nist.gov)

EPSS over time FIRST

Oct 13, 2026 → Oct 14, 2026 · 2 reading(s) · max 0.12%

Detection

Read off the CVSS vector and the weakness class. Starting points, not tested rules.

Local/physical vector: focus on endpoint telemetry (EDR) from affected hosts.

endpoint telemetry (EDR)

Timeline

What happened to this CVE, newest first.

2026
Source status changed · Analyzed → Modified
Oct 15, 2026 · NIST National Vulnerability Database
Affected products added · linux/linux
Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
Record published
Oct 13, 2026
Fix documented
Oct 13, 2026 · NIST National Vulnerability Database
CVSS changed · 5.5
Oct 13, 2026 · NIST National Vulnerability Database
Source status changed · → Analyzed
Oct 13, 2026 · NIST National Vulnerability Database
Record created in this database
Oct 13, 2026 · NIST National Vulnerability Database
CVE published
Jun 25, 2026 · Linux

Source activity

Repeated readings are counted rather than listed.

2× References added · Oct 15, 2026 – Oct 15, 2026
1× Official description updated · Oct 13, 2026 – Oct 13, 2026

References

11 on the record

git.kernel.org/stable/c/e2b8acf9405bd9b1baf1c54dc897b0905db689bf
Patch, NIST National Vulnerability Database
git.kernel.org/stable/c/e05c4ac575b457978a7ef441053394169084869c
Patch, NIST National Vulnerability Database
git.kernel.org/stable/c/b20e8a98dd29b121f58fcdf51e8576119aba536a
Patch, NIST National Vulnerability Database
git.kernel.org/stable/c/fa5823126239b3e453fac1a2fe50726c7f4a55e1
Patch, NIST National Vulnerability Database
git.kernel.org/stable/c/dd214733544427587a95f66dbf3adff072568990
Patch, NIST National Vulnerability Database
git.kernel.org/stable/c/dedc92b96dc1d8919a3bdf2495ede68922ef7ebc
Patch, NIST National Vulnerability Database
git.kernel.org/stable/c/a8335f3db15bd1e0e82e0db5d488fabc7d10d1ab
Patch, NIST National Vulnerability Database
git.kernel.org/stable/c/214a2042b16b3c8d798a8b9ef9f36094f13a9859
Patch, NIST National Vulnerability Database
github.com/advisories/GHSA-hhxp-r7j7-v7jv
GitHub Security Advisories
cert-portal.siemens.com/productcert/html/ssa-784472.html
NIST National Vulnerability Database
nvd.nist.gov/vuln/detail/CVE-2026-53208
GitHub Security Advisories

Elsewhere on this site

Linux
every CVE for this vendor

Related CVEs (same products)

Critical CVE-2026-99999 ipv4: validate checksum_start before completing checksum 7h
Unknown CVE-2026-98432 ipv4: free inet_opt and ireq_opt after an RCU grace period 7h
Unknown CVE-2026-98431 RDMA/uverbs: Fix mmap_lock/disassociation_lock circular dependency 1d
Unknown CVE-2026-98424 wifi: cfg80211: undo netns switch if renaming the wiphy fails 1d
Unknown CVE-2026-98425 wifi: mac80211: don't warn when an IBSS has no channel to scan 1d
Unknown CVE-2026-98426 wifi: mwifiex: fix IRQ leak using wrong index in MSI-X error path 1d

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

No CISA SSVC assessment.
No CWE classification.
No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record

Text assembled only from the fields above — no additional claims.

What should defenders know first?

CVE-2026-53208 is "Bluetooth: L2CAP: reject BR/EDR signaling packets over MTUsig", rated Medium. It affects Linux (Linux); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 5.5 describes technical severity. EPSS 0.12% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.

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