{"cve":"CVE-2026-64127","nvd":{"published":"2026-07-19T16:17:54.387","modified":"2026-08-13T15:11:11.960","status":"Analyzed","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nBluetooth: L2CAP: ecred_reconfigure: send packed pdu, not stack pointer\n\nCommit 1c08108f3014 (\"Bluetooth: L2CAP: Avoid -Wflex-array-member-not-at-end\nwarnings\") converted the on-stack request PDU in l2cap_ecred_reconfigure()\nfrom an explicit packed struct to DEFINE_RAW_FLEX(), but did not adjust the\nsize and source-pointer arguments to l2cap_send_cmd():\n\n  -    struct {\n  -            struct l2cap_ecred_reconf_req req;\n  -            __le16 scid;\n  -    } pdu;\n  +    DEFINE_RAW_FLEX(struct l2cap_ecred_reconf_req, pdu, scid, 1);\n       ...\n       l2cap_send_cmd(conn, chan->ident, L2CAP_ECRED_RECONF_REQ,\n                      sizeof(pdu), &pdu);\n\nAfter the conversion, DEFINE_RAW_FLEX() expands to declare an anonymous\nunion pdu_u plus a local pointer \"pdu\" pointing at it. Therefore:\n\n  - sizeof(pdu) is now sizeof(struct l2cap_ecred_reconf_req *) = 8 on\n    64-bit (4 on 32-bit), not the 6 bytes of (mtu, mps, scid[1]).\n  - &pdu is the address of the local pointer's stack storage, not the\n    address of the request payload.\n\nl2cap_send_cmd() forwards (data, count) to l2cap_build_cmd(), which calls\nskb_put_data(skb, data, count). The L2CAP_ECRED_RECONFIGURE_REQ packet\nbody therefore contains 8 bytes copied from the kernel stack starting at\n&pdu -- the 8 bytes overlap the pdu pointer's value, leaking a kernel\nstack address to the paired Bluetooth peer. The intended (mtu, mps, scid)\nfields are not transmitted at all, so the peer rejects the request as\nmalformed and the L2CAP_ECRED_RECONFIGURE feature itself has been broken\nfor the local-side initiator since the introducing commit landed.\n\nThe sibling site l2cap_ecred_conn_req() in the same commit was converted\ncorrectly (sizeof(*pdu) + len, pdu); only this site was missed.\n\nRestore the original semantics: pass the full flex-struct size via\nstruct_size(pdu, scid, 1) and the pdu pointer (the struct address) as\nthe source.\n\nValidated on a stock 7.0-based host kernel via the real call path:\nsetsockopt(SOL_BLUETOOTH, BT_RCVMTU, ...) on a BT_CONNECTED\nL2CAP_MODE_EXT_FLOWCTL socket emits an L2CAP_ECRED_RECONFIGURE_REQ\nwhose body is 8 bytes (the on-stack pdu local's value) rather than\nthe expected 6. Three captures from fresh socket / fresh hciemu peer\non the same host -- low bytes vary per call, high 0xffff confirms a\nkernel virtual address (KASLR-randomised stack slot, not a fixed\nstring):\n\n  RECONF_REQ body (ident=0x02 len=8): 42 fb 54 af 0e ca ff ff\n  RECONF_REQ body (ident=0x02 len=8): 52 3d 2e af 0e ca ff ff\n  RECONF_REQ body (ident=0x02 len=8): b2 fc 5b af 0e ca ff ff\n\nAfter this patch the body is 6 bytes carrying the expected\nlittle-endian (mtu, mps, scid).","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H","score":5.5},"cwes":[],"references":["https://git.kernel.org/stable/c/051922ab709c0a6917eae765c22481dfc68379e5","https://git.kernel.org/stable/c/3374ef8cf99368a40f7efd51a2a375a4c5dc6f0d","https://git.kernel.org/stable/c/356c9d1a1cbacd2a1640fff3c050e1c3472e924f","https://git.kernel.org/stable/c/ed5fcd2a26f0c16fc289c8cd6b03328a0582a687"],"products":["linux:linux_kernel"],"source":"nvd","synced_at":"2026-10-19T22:45:36.895656543+00:00"},"epss":{"cve":"CVE-2026-64127","score":0.00127,"percentile":0.02391,"date":"2026-10-31"},"kev":null,"osv":[],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}