Capstone is a disassembly framework

Overview

Capstone is a disassembly framework. Prior to version 6.0.0-Alpha9, Capstone's WebAssembly backend accepts attacker-controlled raw WASM instruction bytes through the public cs_disasm() and cs_disasm_iter() APIs. For a large but well-formed br_table instruction, the WASM decoder accumulates the immediate length in a wider local variable but returns it through a uint16_t instruction-size path. When the encoded instruction length is exactly 65,536 bytes, the size wraps to zero and cs_disasm() can repeatedly decode the same instruction without advancing. For larger lengths, cs_disasm_iter() advances into the middle of the br_table payload and decodes target bytes as subsequent instructions. This is an availability and parser-integrity issue. Version 6.0.0-Alpha9 patches the issue.

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.

Vendor advisories

• RHSA-2026:81540 · Red Hat · fixed in: Red Hat Hardened Images · released 2026-10-12 · advisory
• Red Hat VEX · Moderate · affected: Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 9, Red Hat OpenShift Container Platform 4 · no fix planned: Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 9, Red Hat OpenShift Container Platform 4 · updated 2026-10-16 · vex