CVE-2026-64126 in Linux
Summary
by MITRE • 07/19/2026
In the Linux kernel, the following vulnerability has been resolved:
Bluetooth: MGMT: validate Add Extended Advertising Data length
MGMT_OP_ADD_EXT_ADV_DATA is registered as a variable-length command, with MGMT_ADD_EXT_ADV_DATA_SIZE as the fixed header size. The handler then uses cp->adv_data_len and cp->scan_rsp_len to validate and copy cp->data, but it never checks that those bytes are part of the mgmt command payload.
A short command can therefore make add_ext_adv_data() pass an out-of-bounds pointer into tlv_data_is_valid(). If the bytes beyond the command buffer are addressable, they can also be copied into the advertising instance as scan response data, where the caller can read them back via MGMT_OP_GET_ADV_INSTANCE. The trigger requires CAP_NET_ADMIN in the initial user namespace; KASAN reports an 8-byte slab-out-of-bounds read.
Reject commands whose length does not match the fixed header plus both advertising data lengths before parsing cp->data.
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Analysis
by VulDB Data Team • 07/19/2026
This vulnerability exists within the Linux kernel's Bluetooth management subsystem where the MGMT_OP_ADD_EXT_ADV_DATA command processing fails to properly validate command buffer boundaries. The flaw occurs because the command handler treats the operation as variable-length while registering it with a fixed header size of MGMT_ADD_EXT_ADV_DATA_SIZE. The system uses cp->adv_data_len and cp->scan_rsp_len fields to validate and copy data from cp->data without ensuring these length values fall within the actual command payload boundaries. This oversight creates a potential out-of-bounds memory access scenario where malformed commands can reference memory beyond the allocated buffer space.
The technical implementation issues stem from improper input validation in the Bluetooth management interface handler function add_ext_adv_data(). When processing commands with insufficient length, the system accepts potentially invalid data pointers that reference memory regions outside the intended command buffer. This condition allows for slab-out-of-bounds read operations as reported by KASAN memory error detection tools, where 8-byte reads occur beyond valid memory slabs. The vulnerability manifests through a classic buffer overflow pattern where the validation logic fails to check if the combined length of advertising data and scan response data fits within the declared command size.
Operational impact of this vulnerability extends beyond simple memory corruption as it provides potential information disclosure capabilities. An attacker with CAP_NET_ADMIN capability in the initial user namespace can craft malicious commands that cause the kernel to read arbitrary memory locations and subsequently expose this data through the MGMT_OP_GET_ADV_INSTANCE operation. This creates a situation where sensitive information from kernel memory spaces could be retrieved by unauthorized parties, potentially leading to privilege escalation or information leakage. The vulnerability affects the Bluetooth management interface specifically and requires elevated privileges to exploit effectively.
The mitigation strategy involves implementing strict command length validation before any data processing occurs in the add_ext_adv_data() handler function. This requires checking that the total command length equals the fixed header size plus the sum of advertising data length and scan response length fields. When the declared lengths exceed the actual buffer boundaries, the command should be rejected immediately rather than processed, preventing out-of-bounds memory operations from occurring. This approach follows established security practices for input validation and aligns with common CWE categories related to buffer overflows and improper input validation. The fix directly addresses ATT&CK technique T1068 by preventing privilege escalation through kernel memory corruption vulnerabilities.
This vulnerability represents a classic case of insufficient input validation in kernel-space code processing, where proper boundary checking should occur before any data manipulation operations. The flaw demonstrates how variable-length command processing can introduce security risks when not properly validated against actual buffer boundaries. The requirement for CAP_NET_ADMIN privileges limits the attack surface but does not eliminate the risk entirely, as this capability is often available to processes running with elevated privileges in many system configurations. The memory safety issue has been classified according to CWE-129 and CWE-787 categories related to insufficient validation of length fields and out-of-bounds reads respectively, highlighting the fundamental importance of robust input validation in kernel security.