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CVE-2026-55893: Capstone SH disassembler `set_reg_n` heap buffer overflow via crafted SH2A FPU bytecode

• Severity: high (CVSS 7.3 v4.0)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.2% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-08-20 · updated 2026-10-18
• Weakness: CWE-122

Description

Capstone is a disassembly framework. In 6.0.0-Alpha9 and earlier, Capstone's arch/SH/SHDisassembler.c SH floating-point decoders such as opFADD, opFMUL, and opFSUB call set_reg() and set_reg_n() using sh_info.op.op_count without checking the fixed-size operands[] array. Repeated crafted instructions processed through cs_disasm_iter() or cs_disasm() with CS_ARCH_SH, CS_MODE_SH2A or CS_MODE_SH4A, CS_MODE_SHFPU, and CS_OPT_DETAIL can increment the operand count beyond the 176-byte sh_info allocation and perform a four-byte heap buffer overflow write. The corruption can crash the process and may enable code execution depending on heap layout. This issue is fixed in version 6.0.0-Alpha10.

Affected products

• capstone-engine capstone: before 6.0.0-Alpha10

References

• https://github.com/capstone-engine/capstone/commit/09e76802380b9e94d9720c44458d9d5282219e7e
• https://github.com/capstone-engine/capstone/commit/e17ee44a8307ea33375b4727ac4f987650bf7bed
• https://github.com/capstone-engine/capstone/pull/2968
• https://github.com/capstone-engine/capstone/pull/2969
• https://github.com/capstone-engine/capstone/releases/tag/6.0.0-Alpha10
• https://github.com/capstone-engine/capstone/security/advisories/GHSA-3hpv-wr3j-rxwh

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