---
id: CVE-2026-31498
title: 'Bluetooth: L2CAP: Fix ERTM re-init and zero pdu_len infinite loop'
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  Bluetooth: L2CAP: Fix ERTM re-init and zero pdu_len infinite loop

  l2cap_config_req() processes CONFIG_REQ for channels in BT_CONNECTED
  state to support L2CAP reconfigu…
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= 96298f640104e4cd9a913a6e50b0b981829b94ff <
    9760b83cfd24b38caee663f429011a0dd6064fa9
  - >-
    Linux >= 96298f640104e4cd9a913a6e50b0b981829b94ff <
    de37e2655b7abc3f59254c6b72256840f39fc6d5
  - >-
    Linux >= 96298f640104e4cd9a913a6e50b0b981829b94ff <
    e7aab23b7df89a3d754a5f0a7d2237548b328bd0
  - >-
    Linux >= 96298f640104e4cd9a913a6e50b0b981829b94ff <
    52667c859fe33f70c2e711cb81bbd505d5eb8e75
  - >-
    Linux >= 96298f640104e4cd9a913a6e50b0b981829b94ff <
    9a21a631ee034b1573dce14b572a24943dbfd7ae
  - >-
    Linux >= 96298f640104e4cd9a913a6e50b0b981829b94ff <
    900e4db5385ec2cacd372345a80ab9c8e105b3a3
  - >-
    Linux >= 96298f640104e4cd9a913a6e50b0b981829b94ff <
    042e2cd4bb11e5313b19b87593616524949e4c52
  - >-
    Linux >= 96298f640104e4cd9a913a6e50b0b981829b94ff <
    25f420a0d4cfd61d3d23ec4b9c56d9f443d91377
  - Linux 4ad03ff6f680681c5f78254e37c4c856fa953629
  - Linux b7d0ca715c1008acd2fc018f02a56fed88f78b75
  - Linux 799263eb37a4f7f6d39334046929c3bc92452a7f
  - Linux 8828622fb9b4201eeb0870587052e3d834cfaf61
  - Linux b432ea85ab8472763870dd0f2c186130dd36d68c
  - Linux >= 4.4.238 < 4.5
  - Linux >= 4.9.238 < 4.10
  - Linux >= 4.14.200 < 4.15
  - Linux >= 4.19.149 < 4.20
  - Linux >= 5.4.69 < 5.5
  - Linux 5.7
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: partial
  timestamp: '2026-11-05T21:35:45.390526Z'
published: '2026-04-22'
updated: '2026-11-05'
sourceUpdated: '2026-11-05T21:45:03.103Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-31498'
references:
  - url: 'https://git.kernel.org/stable/c/9760b83cfd24b38caee663f429011a0dd6064fa9'
  - url: 'https://git.kernel.org/stable/c/de37e2655b7abc3f59254c6b72256840f39fc6d5'
  - url: 'https://git.kernel.org/stable/c/e7aab23b7df89a3d754a5f0a7d2237548b328bd0'
  - url: 'https://git.kernel.org/stable/c/52667c859fe33f70c2e711cb81bbd505d5eb8e75'
  - url: 'https://git.kernel.org/stable/c/9a21a631ee034b1573dce14b572a24943dbfd7ae'
  - url: 'https://git.kernel.org/stable/c/900e4db5385ec2cacd372345a80ab9c8e105b3a3'
  - url: 'https://git.kernel.org/stable/c/042e2cd4bb11e5313b19b87593616524949e4c52'
  - url: 'https://git.kernel.org/stable/c/25f420a0d4cfd61d3d23ec4b9c56d9f443d91377'
tags:
  - cve.org
epss: 0.00123
epssPercentile: 0.02054
ingestedAt: '2026-11-05T23:41:31.985Z'
---

## Overview

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

Bluetooth: L2CAP: Fix ERTM re-init and zero pdu_len infinite loop

l2cap_config_req() processes CONFIG_REQ for channels in BT_CONNECTED
state to support L2CAP reconfiguration (e.g. MTU changes). However,
since both CONF_INPUT_DONE and CONF_OUTPUT_DONE are already set from
the initial configuration, the reconfiguration path falls through to
l2cap_ertm_init(), which re-initializes tx_q, srej_q, srej_list, and
retrans_list without freeing the previous allocations and sets
chan->sdu to NULL without freeing the existing skb. This leaks all
previously allocated ERTM resources.

Additionally, l2cap_parse_conf_req() does not validate the minimum
value of remote_mps derived from the RFC max_pdu_size option. A zero
value propagates to l2cap_segment_sdu() where pdu_len becomes zero,
causing the while loop to never terminate since len is never
decremented, exhausting all available memory.

Fix the double-init by skipping l2cap_ertm_init() and
l2cap_chan_ready() when the channel is already in BT_CONNECTED state,
while still allowing the reconfiguration parameters to be updated
through l2cap_parse_conf_req(). Also add a pdu_len zero check in
l2cap_segment_sdu() as a safeguard.

## Affected

- `Linux >= 96298f640104e4cd9a913a6e50b0b981829b94ff < 9760b83cfd24b38caee663f429011a0dd6064fa9`
- `Linux >= 96298f640104e4cd9a913a6e50b0b981829b94ff < de37e2655b7abc3f59254c6b72256840f39fc6d5`
- `Linux >= 96298f640104e4cd9a913a6e50b0b981829b94ff < e7aab23b7df89a3d754a5f0a7d2237548b328bd0`
- `Linux >= 96298f640104e4cd9a913a6e50b0b981829b94ff < 52667c859fe33f70c2e711cb81bbd505d5eb8e75`
- `Linux >= 96298f640104e4cd9a913a6e50b0b981829b94ff < 9a21a631ee034b1573dce14b572a24943dbfd7ae`
- `Linux >= 96298f640104e4cd9a913a6e50b0b981829b94ff < 900e4db5385ec2cacd372345a80ab9c8e105b3a3`
- `Linux >= 96298f640104e4cd9a913a6e50b0b981829b94ff < 042e2cd4bb11e5313b19b87593616524949e4c52`
- `Linux >= 96298f640104e4cd9a913a6e50b0b981829b94ff < 25f420a0d4cfd61d3d23ec4b9c56d9f443d91377`
- `Linux 4ad03ff6f680681c5f78254e37c4c856fa953629`
- `Linux b7d0ca715c1008acd2fc018f02a56fed88f78b75`
- `Linux 799263eb37a4f7f6d39334046929c3bc92452a7f`
- `Linux 8828622fb9b4201eeb0870587052e3d834cfaf61`
- `Linux b432ea85ab8472763870dd0f2c186130dd36d68c`
- `Linux >= 4.4.238 < 4.5`
- `Linux >= 4.9.238 < 4.10`
- `Linux >= 4.14.200 < 4.15`
- `Linux >= 4.19.149 < 4.20`
- `Linux >= 5.4.69 < 5.5`
- `Linux 5.7`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.