CVE-2026-63893 in Linux
Summary
by MITRE • 07/19/2026
In the Linux kernel, the following vulnerability has been resolved:
thunderbolt: property: Reject u32 wrap in tb_property_entry_valid()
entry->value is u32 and entry->length is u16; the sum is performed in u32 and wraps. A malicious XDomain peer can pick value = 0xffffff00, length = 0x100 so the sum 0x100000000 wraps to 0 and passes the > block_len check. tb_property_parse() then passes entry->value to parse_dwdata() as a dword offset into the property block, reading attacker-directed memory far past the allocation.
For TEXT-typed entries with the "deviceid" or "vendorid" keys this lands in xd->device_name / xd->vendor_name and is readable back via the per-XDomain device_name / vendor_name sysfs attributes; the leak is NUL-bounded (kstrdup() stops at the first zero byte) and untargeted (the attacker picks a delta, not an absolute address). DATA-typed entries are parsed into property->value.data but not generically surfaced to userspace.
Use check_add_overflow() so a wrapped sum is rejected.
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Analysis
by VulDB Data Team • 07/19/2026
The vulnerability exists in the linux kernel's thunderbolt subsystem within the tb_property_entry_valid() function where a critical arithmetic overflow occurs during property validation. This flaw stems from improper handling of data type conversions between u32 and u16 values, creating a condition where attacker-controlled inputs can manipulate the validation logic through integer wraparound behavior. The vulnerability specifically affects the thunderbolt driver's ability to properly validate property entries in XDomain peer connections, representing a direct security risk in hardware communication protocols.
The technical implementation of this vulnerability exploits a classic integer overflow scenario where entry->value is a u32 type and entry->length is a u16 type, but their sum operation occurs in u32 context causing wraparound behavior. An attacker controlling a malicious XDomain peer can construct a specific payload with value = 0xffffff00 and length = 0x100, resulting in a sum of 0x100000000 that wraps to zero due to unsigned integer overflow. This zero result passes the > block_len check, allowing malformed entries to proceed through validation and into subsequent parsing routines.
When tb_property_parse() processes these malicious entries, it passes entry->value directly to parse_dwdata() as a dword offset within the property block, causing memory reads that extend far beyond allocated boundaries. The exploitation targets memory regions containing device identification data where TEXT-typed entries with "deviceid" or "vendorid" keys map to xd->device_name and xd->vendor_name fields accessible through sysfs attributes. This creates a information disclosure vulnerability allowing attackers to read memory contents through controlled offsets, though the leak is limited by kstrdup() behavior which stops at null bytes and lacks precise targeting capabilities.
The operational impact of this vulnerability spans multiple security domains including information disclosure, privilege escalation potential, and hardware communication integrity threats. The flaw represents a CWE-190 type integer overflow that enables attackers to perform out-of-bounds memory reads in kernel space, potentially exposing sensitive system information or facilitating further exploitation through data leakage. The vulnerability affects systems using thunderbolt hardware interfaces where XDomain peer connections are established, creating persistent security risks for devices supporting this communication protocol.
The recommended mitigation involves implementing proper overflow detection using check_add_overflow() macro to prevent wraparound behavior during arithmetic operations between different sized integer types. This approach aligns with secure coding practices outlined in various cybersecurity frameworks and ATT&CK techniques related to kernel exploit development and privilege escalation. The fix ensures that any arithmetic operation producing a result exceeding the maximum representable value for the target type will be properly rejected, preventing malicious inputs from bypassing validation checks. This solution addresses the root cause while maintaining system functionality through proper integer handling and overflow protection mechanisms.
The vulnerability demonstrates typical characteristics of kernel-level security flaws in hardware subsystems where improper input validation combined with arithmetic operations creates exploitable conditions. Similar patterns have been documented in other kernel subsystems and represent common attack vectors for privilege escalation and information disclosure attacks, making this fix crucial for maintaining system security boundaries and protecting against sophisticated adversarial exploitation techniques targeting hardware interface drivers.