High severity · published May 1, 2026
CVE-2026-31773
Bluetooth: SMP: derive legacy responder STK authentication from MITM state
8.8
CVSS
0.3%
EPSS
No
On KEV
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.
CVSS vector
CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Attack vector
Adjacent
Complexity
Low
Privileges
None
User interaction
None
Confidentiality
High
Integrity
High
Availability
High
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.3% · higher than 20% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
KE
Kernel · Linux
3.15.5 before 3.16; 3.16.1 before 5.10.253; 5.11 before 5.15.203; 5.16 before 6.1.168; 6.2 before 6.6.134; 6.7 before 6.12.81; +9 more · source: NVD
LI
Linux · Linux
fff3490f47810e2d34b91fb9e31103e923b11c2f before 9a38659a3d06080715691bd3139f9c4b61f688e3; fff3490f47810e2d34b91fb9e31103e923b11c2f before 667f44f1392df6482483756458c48670e579e9ff; fff3490f47810e2d34b91fb9e31103e923b11c2f before 929db734d12db41ca5f95424db4612397f1bd4a7; fff3490f47810e2d34b91fb9e31103e923b11c2f before b1c6a8e554a39b222c0879a288ea98e338fc4d77; fff3490f47810e2d34b91fb9e31103e923b11c2f before 0afc846bd80073ffcd2b8040f2b2fafaea3d9f72; fff3490f47810e2d34b91fb9e31103e923b11c2f before 061ee71ac6b03c9f8432fe49538c3682bfcf4cf3; +5 more · source: vendor
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-31773
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-31773
Patch
https://git.kernel.org/stable/c/061ee71ac6b03c9f8432fe49538c3682bfcf4cf3
Patch
https://git.kernel.org/stable/c/0afc846bd80073ffcd2b8040f2b2fafaea3d9f72
Patch
https://git.kernel.org/stable/c/20756fec2f0108cb88e815941f1ffff88dc286fe
Patch
https://git.kernel.org/stable/c/667f44f1392df6482483756458c48670e579e9ff
Patch
https://git.kernel.org/stable/c/929db734d12db41ca5f95424db4612397f1bd4a7
Patch
https://git.kernel.org/stable/c/9a38659a3d06080715691bd3139f9c4b61f688e3
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