CVE-2026-64354 in Linux
Summary
by MITRE • 07/25/2026
In the Linux kernel, the following vulnerability has been resolved:
bpf: Validate BTF repeated field counts before expansion
btf_parse_struct_metas() walks user-supplied BTF during BPF_BTF_LOAD, and btf_repeat_fields() expands repeatable fields from array elements into the fixed BTF_FIELDS_MAX scratch array used by btf_parse_fields().
The remaining-capacity check performs the expanded field count calculation in u32. A malformed BTF can wrap that calculation, causing the check to pass even when the expanded field count exceeds the scratch array capacity. The following memcpy() can then write past the end of the array.
Use checked addition and multiplication before copying repeated fields and reject impossible counts.
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Analysis
by VulDB Data Team • 07/25/2026
The vulnerability resides in the Linux kernel's eBPF (extended Berkeley Packet Filter) subsystem, specifically within the BTF (BPF Type Format) parsing functionality that handles BPF_BTF_LOAD operations. This flaw demonstrates a classic buffer overflow condition occurring during the processing of user-supplied BTF data structures. The issue manifests when btf_parse_struct_metas() function iterates through user-provided BTF information and calls btf_repeat_fields() to expand array elements into a fixed-size scratch array named BTF_FIELDS_MAX. The core problem emerges from insufficient validation of field count calculations that occur during this expansion process, creating a potential for arbitrary code execution or system instability.
The technical implementation flaw involves an arithmetic overflow condition where the capacity check for the scratch array performs expanded field count calculations using 32-bit unsigned integers. This design choice allows for integer wraparound scenarios when malformed BTF data attempts to manipulate the field count calculation logic. When the calculation wraps around from maximum u32 values back to zero, the validation logic incorrectly passes the capacity check despite the actual expanded field count exceeding the allocated BTF_FIELDS_MAX scratch array limits. This vulnerability directly maps to CWE-190, Integer Overflow or Wraparound, and potentially CWE-787, Out-of-bounds Write, as the subsequent memcpy() operation can overwrite memory beyond the intended array boundaries.
Operationally, this vulnerability presents a significant security risk within kernel space execution environments where eBPF programs are loaded. Attackers could craft malicious BTF data structures that exploit this overflow condition to overwrite adjacent memory locations, potentially leading to privilege escalation or system compromise. The impact extends beyond simple denial of service since the vulnerable code path operates in kernel context with elevated privileges. This vulnerability aligns with ATT&CK technique T1059.006 for kernel-mode rootkits and T1547.001 for privilege escalation through kernel exploits, making it particularly dangerous in containerized environments or systems where untrusted users can load BPF programs.
The mitigation strategy requires implementing checked arithmetic operations before any field expansion occurs during the BTF loading process. This includes using safe addition and multiplication operations that detect overflow conditions before proceeding with memory copying operations. The fix must validate that repeated field counts are mathematically feasible and reject any impossible combinations that could lead to buffer overflows. Additionally, proper bounds checking should be implemented at multiple levels including pre-expansion validation of user-supplied data structures and post-expansion verification of memory access patterns. This approach directly addresses the underlying integer overflow issue while maintaining compatibility with legitimate BTF structures and preventing exploitation through malformed input data that would otherwise bypass the capacity validation checks.