CVE-2026-49263 capstone-engine CVE debrief

Who should care

Defenders handling WebAssembly content, especially those using the Capstone disassembly framework, should assess exposure and prioritize updating to version 6.0.0-Alpha9 or later. This involves verifying and updating Capstone, reviewing systems for potential exposure, and monitoring for parser-integrity issues. Defenders should also review the official advisory or CVE record to validate affected scope, severity, and vendor guidance. Additionally, they

Why it matters

Defenders should care about CVE-2026-49263 because it affects the Capstone disassembly framework's WebAssembly backend, potentially leading to parser-integrity issues and incorrect instruction decoding. This requires verification of exposure and prioritization of updates to version 6.0.0-Alpha9 or later, especially in systems handling WebAssembly content.

• Parser-integrity compromise potentially leading to incorrect instruction decoding
• Repeated decoding of the same instruction without advancing
• Advancing into the middle of the `br_table` payload and decoding target bytes as subsequent instructions

Technical summary

The Capstone disassembly framework's WebAssembly backend has an issue where it accepts attacker-controlled raw WASM instruction bytes through public APIs. For specific `br_table` instruction lengths, the decoder may accumulate and return incorrect instruction sizes, leading to repeated decoding or advancing into the middle of the `br_table` payload. This issue is patched in version 6.0.0-Alpha9. The issue arises from the public `cs_disasm()` and `cs_disasm_iter()` APIs accepting attacker-controlled raw WASM instruction bytes. 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.

Defensive priority

Defenders should prioritize verifying and updating Capstone to version 6.0.0-Alpha9 or later, especially in systems handling WebAssembly content.

Recommended defensive actions

• Verify and update Capstone to version 6.0.0-Alpha9 or later
• Review systems handling WebAssembly content for potential exposure
• Monitor for and address any parser-integrity issues
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up
• Review the supplied official advisory or CVE record to validate affected scope, severity, and vendor guidance
• Plan vendor-supported updates or mitigations through normal change control where exposure is confirmed
• Check relevant monitoring, detection, and logs for exposed assets that need extra review

Evidence notes

The issue is confirmed through the CVE and NVD records, as well as references to the Capstone project's changelog and security advisory. The CVE record provides official metadata, while the NVD detail page offers a source-specific vulnerability assessment. The Capstone project's changelog and security advisory provide additional context on the patched issue. Defenders should verify exposure and prioritize updates to version 6.0.0-Alpha9 or later, especially in systems handling WebAssembly content. This involves reviewing the official

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.