# CVE-2026-31498: Bluetooth: L2CAP: Fix ERTM re-init and zero pdu_len infinite loop

Status: published. Published: 2026-04-22. Updated: 2026-11-05.

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.

## Remediation

No remediation reported in collected sources

## Affected products and versions

- Linux / Linux: ≥ 96298f640104e4cd9a913a6e50b0b981829b94ff; < 9760b83cfd24b38caee663f429011a0dd6064fa9 (affected, git); ≥ 96298f640104e4cd9a913a6e50b0b981829b94ff; < de37e2655b7abc3f59254c6b72256840f39fc6d5 (affected, git); ≥ 96298f640104e4cd9a913a6e50b0b981829b94ff; < e7aab23b7df89a3d754a5f0a7d2237548b328bd0 (affected, git); ≥ 96298f640104e4cd9a913a6e50b0b981829b94ff; < 52667c859fe33f70c2e711cb81bbd505d5eb8e75 (affected, git); ≥ 96298f640104e4cd9a913a6e50b0b981829b94ff; < 9a21a631ee034b1573dce14b572a24943dbfd7ae (affected, git); ≥ 96298f640104e4cd9a913a6e50b0b981829b94ff; < 900e4db5385ec2cacd372345a80ab9c8e105b3a3 (affected, git); ≥ 96298f640104e4cd9a913a6e50b0b981829b94ff; < 042e2cd4bb11e5313b19b87593616524949e4c52 (affected, git); ≥ 96298f640104e4cd9a913a6e50b0b981829b94ff; < 25f420a0d4cfd61d3d23ec4b9c56d9f443d91377 (affected, git); 4ad03ff6f680681c5f78254e37c4c856fa953629 (affected, git); b7d0ca715c1008acd2fc018f02a56fed88f78b75 (affected, git); 799263eb37a4f7f6d39334046929c3bc92452a7f (affected, git); 8828622fb9b4201eeb0870587052e3d834cfaf61 (affected, git); b432ea85ab8472763870dd0f2c186130dd36d68c (affected, git); ≥ 4.4.238; < 4.5 (affected, semver); ≥ 4.9.238; < 4.10 (affected, semver); ≥ 4.14.200; < 4.15 (affected, semver); ≥ 4.19.149; < 4.20 (affected, semver); ≥ 5.4.69; < 5.5 (affected, semver). Source: CNA: Linux
- Linux / Linux: 5.7 (affected); ≥ 0; < 5.7 (unaffected, semver); ≥ 5.10.253; ≤ 5.10.* (unaffected, semver); ≥ 5.15.203; ≤ 5.15.* (unaffected, semver); ≥ 6.1.168; ≤ 6.1.* (unaffected, semver); ≥ 6.6.131; ≤ 6.6.* (unaffected, semver); ≥ 6.12.80; ≤ 6.12.* (unaffected, semver); ≥ 6.18.21; ≤ 6.18.* (unaffected, semver); ≥ 6.19.11; ≤ 6.19.* (unaffected, semver); ≥ 7.0; ≤ * (unaffected, original_commit_for_fix). Source: CNA: Linux

## Severity and prioritization

- CISA KEV: No listing in collected sources

- EPSS: 0.12% as of 2026-11-05; percentile 2.04%

- SSVC: exploitation none; automatable no; technical impact partial; source ADP: CISA-ADP

- Weaknesses: Not reported

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://git.kernel.org/stable/c/9760b83cfd24b38caee663f429011a0dd6064fa9 (CNA: Linux)

- https://git.kernel.org/stable/c/de37e2655b7abc3f59254c6b72256840f39fc6d5 (CNA: Linux)

- https://git.kernel.org/stable/c/e7aab23b7df89a3d754a5f0a7d2237548b328bd0 (CNA: Linux)

- https://git.kernel.org/stable/c/52667c859fe33f70c2e711cb81bbd505d5eb8e75 (CNA: Linux)

- https://git.kernel.org/stable/c/9a21a631ee034b1573dce14b572a24943dbfd7ae (CNA: Linux)

- https://git.kernel.org/stable/c/900e4db5385ec2cacd372345a80ab9c8e105b3a3 (CNA: Linux)

- https://git.kernel.org/stable/c/042e2cd4bb11e5313b19b87593616524949e4c52 (CNA: Linux)

- https://git.kernel.org/stable/c/25f420a0d4cfd61d3d23ec4b9c56d9f443d91377 (CNA: Linux)

## Provenance

- CNA: Linux: https://www.cve.org/CVERecord?id=CVE-2026-31498; retrieved 2026-11-05; source updated 2026-11-05

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2026-31498; retrieved 2026-11-05; source updated Not reported

Revision: 7043c573d47af3d0a68fe2b8f5ba1be0917838958474bd6f3794b53f89e92021

Canonical: https://y2.dev/cve/CVE-2026-31498

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