capstone-engine vulnerabilities and threats

CVE-2026-55894 is an out-of-bounds read vulnerability in the capstone disassembly framework affecting versions before 6.0.0-Alpha10. The flaw occurs in the SHDisassembler.c sh_disassemble() function where an index computed from a 16-bit instruction is not properly validated against the decode function-pointer table. This can lead to a segmentation fault and process termination when processing crafted bytecode with specific SH architecture modes. No code execution or information disclosure has been demonstrated. The issue is fixed in version 6.0.0-Alpha10.

A heap-based buffer overflow vulnerability exists in capstone-engine versions prior to 6.0.0-Alpha10 in the SH floating-point decoders. The issue arises when crafted instructions cause the operand count to exceed the allocated buffer size, leading to a four-byte overflow. This can crash the process and potentially allow code execution depending on heap layout. The vulnerability is fixed in version 6.0.0-Alpha10.

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.

Capstone is a disassembly framework. Prior to version 6.0.0-Alpha9, Capstone's public `cs_insn_name()` API forwards caller-supplied instruction IDs directly to the selected architecture backend. Most backends validate the ID before indexing instruction-name tables, but the M68K and RISCV backends have missing or incomplete bounds checks. On a Capstone handle opened for M68K or RISCV, a caller-controlled invalid instruction ID can trigger an out-of-bounds read and crash the process. The demonstrated impact is availability loss in applications or bindings that expose instruction-name lookup to untrusted IDs. No code execution or data disclosure was demonstrated. Version 6.0.0-Alpha9 patches the issue.

Capstone is a disassembly framework. Versions prior to 6.0.0-Alpha8 and 5.0.8 have a NULL pointer dereference in `modRMRequired()` and `decode()` when disassembling 3DNow! opcodes (`0F 0F`) in builds compiled with `-DCAPSTONE_X86_REDUCE`, allowing a remote attacker to crash any application using the reduced X86 Capstone library by supplying a crafted input containing the 4-byte sequence `0F 0F <modrm> <imm8>`. Versions 6.0.0-Alpha8 and 5.0.8 patch the issue.

Capstone is a disassembly framework. In versions 6.0.0-Alpha5 and prior, an unchecked vsnprintf return in SStream_concat lets a malicious cs_opt_mem.vsnprintf drive SStream’s index negative or past the end, leading to a stack buffer underflow/overflow when the next write occurs. Commit 2c7797182a1618be12017d7d41e0b6581d5d529e fixes the issue.

Capstone is a disassembly framework. In versions 6.0.0-Alpha5 and prior, Skipdata length is not bounds-checked, so a user-provided skipdata callback can make cs_disasm/cs_disasm_iter memcpy more than 24 bytes into cs_insn.bytes, causing a heap buffer overflow in the disassembly path. Commit cbef767ab33b82166d263895f24084b75b316df3 fixes the issue.