What’s Vulnerable › Vulnerabilities

CVE-2026-49263: Capstone WASM `br_table` instruction-size truncation can cause no-progress disassembly and parser desynchronization

• Severity: low (CVSS 2.0 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: 2026-08-14 · updated 2026-09-18
• Weakness: CWE-197

Description

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.

Affected products

• capstone-engine capstone: before 6.0.0-Alpha9

References

• https://github.com/capstone-engine/capstone/blob/251c5bb4bc9bb92973e738ae3c5f4ef86f103356/ChangeLog#L102
• https://github.com/capstone-engine/capstone/security/advisories/GHSA-5m9f-vqcm-g5pr
• https://github.com/capstone-engine/capstone/security/advisories/GHSA-5m9f-vqcm-g5pr

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