CVE-2026-31773

Bluetooth: SMP: derive legacy responder STK authentication from MITM state

State: Published
Severity: 8.8 High
Published: May 1, 2026
Updated: Oct 19, 2026
Reserved: Mar 9, 2026

Description

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

Bluetooth: SMP: derive legacy responder STK authentication from MITM state

The legacy responder path in smp_random() currently labels the stored STK as authenticated whenever pending_sec_level is BT_SECURITY_HIGH. That reflects what the local service requested, not what the pairing flow actually achieved.

For Just Works/Confirm legacy pairing, SMP_FLAG_MITM_AUTH stays clear and the resulting STK should remain unauthenticated even if the local side requested HIGH security. Use the established MITM state when storing the responder STK so the key metadata matches the pairing result.

This also keeps the legacy path aligned with the Secure Connections code, which already treats JUST_WORKS/JUST_CFM as unauthenticated.

Scores

CVSS	Score	Vector	Source
3.1	8.8 High	CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H	Linux

Weaknesses

CWE-287 Improper Authentication

Affected Products

Product	Versions
LinuxLinux	fff3490f47810e2d34b91fb9e31103e923b11c2f to before 9a38659a3d06080715691bd3139f9c4b61f688e3Affected fff3490f47810e2d34b91fb9e31103e923b11c2f to before 667f44f1392df6482483756458c48670e579e9ffAffected fff3490f47810e2d34b91fb9e31103e923b11c2f to before 929db734d12db41ca5f95424db4612397f1bd4a7Affected fff3490f47810e2d34b91fb9e31103e923b11c2f to before b1c6a8e554a39b222c0879a288ea98e338fc4d77Affected fff3490f47810e2d34b91fb9e31103e923b11c2f to before 0afc846bd80073ffcd2b8040f2b2fafaea3d9f72Affected fff3490f47810e2d34b91fb9e31103e923b11c2f to before 061ee71ac6b03c9f8432fe49538c3682bfcf4cf3Affected fff3490f47810e2d34b91fb9e31103e923b11c2f to before 9a6d0db176f082685e0b6149700c0baf3ce2aa8bAffected fff3490f47810e2d34b91fb9e31103e923b11c2f to before 20756fec2f0108cb88e815941f1ffff88dc286feAffected 14ec593d6bb050cf40a4ade2f9ac9ca050e0412cAffected 3.15.5 to before 3.16Affected
LinuxLinux	3.16Affected before 3.16Not affected 5.10.253 through 5.10.Not affected 5.15.203 through 5.15.Not affected 6.1.168 through 6.1.Not affected 6.6.134 through 6.6.Not affected 6.12.81 through 6.12.Not affected 6.18.22 through 6.18.Not affected 6.19.12 through 6.19.*Not affected 7.0 and laterNot affected

Product

Versions

LinuxLinux

fff3490f47810e2d34b91fb9e31103e923b11c2f to before 9a38659a3d06080715691bd3139f9c4b61f688e3Affected
fff3490f47810e2d34b91fb9e31103e923b11c2f to before 667f44f1392df6482483756458c48670e579e9ffAffected
fff3490f47810e2d34b91fb9e31103e923b11c2f to before 929db734d12db41ca5f95424db4612397f1bd4a7Affected
fff3490f47810e2d34b91fb9e31103e923b11c2f to before b1c6a8e554a39b222c0879a288ea98e338fc4d77Affected
fff3490f47810e2d34b91fb9e31103e923b11c2f to before 0afc846bd80073ffcd2b8040f2b2fafaea3d9f72Affected
fff3490f47810e2d34b91fb9e31103e923b11c2f to before 061ee71ac6b03c9f8432fe49538c3682bfcf4cf3Affected
fff3490f47810e2d34b91fb9e31103e923b11c2f to before 9a6d0db176f082685e0b6149700c0baf3ce2aa8bAffected
fff3490f47810e2d34b91fb9e31103e923b11c2f to before 20756fec2f0108cb88e815941f1ffff88dc286feAffected
14ec593d6bb050cf40a4ade2f9ac9ca050e0412cAffected
3.15.5 to before 3.16Affected

LinuxLinux

3.16Affected
before 3.16Not affected
5.10.253 through 5.10.*Not affected
5.15.203 through 5.15.*Not affected
6.1.168 through 6.1.*Not affected
6.6.134 through 6.6.*Not affected
6.12.81 through 6.12.*Not affected
6.18.22 through 6.18.*Not affected
6.19.12 through 6.19.*Not affected
7.0 and laterNot affected

References

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