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

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-49263
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-08-14 18:17:30 UTC
Updated2026-08-17 20:16:43 UTC
DescriptionCapstone 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.

Risk And Classification

Primary CVSS: v4.0 2 LOW from [email protected]

CVSS:4.0/AV:L/AC:L/AT:P/PR:N/UI:P/VC:N/VI:L/VA:L/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

EPSS: 0.001280000 probability, percentile 0.029080000 (date 2026-08-18)

Problem Types: CWE-197 | CWE-197 CWE-197: Numeric Truncation Error

VersionSourceTypeScoreSeverityVector
4.0[email protected]Secondary2LOWCVSS:4.0/AV:L/AC:L/AT:P/PR:N/UI:P/VC:N/VI:L/VA:L/SC:N/SI:N/SA:N/E:X/C...
4.0CNADECLARED2LOWCVSS:4.0/AV:L/AC:L/AT:P/PR:N/UI:P/VC:N/VI:L/VA:L/SC:N/SI:N/SA:N

CVSS v4.0 Breakdown

Attack Vector
Local
Attack Complexity
Low
Attack Requirements
Present
Privileges Required
None
User Interaction
Passive
Confidentiality
None
Integrity
Low
Availability
Low
Sub Conf.
None
Sub Integrity
None
Sub Availability
None

CVSS:4.0/AV:L/AC:L/AT:P/PR:N/UI:P/VC:N/VI:L/VA:L/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Capstone-engine Capstone affected < 6.0.0-Alpha9 Not specified

References

ReferenceSourceLinkTags
github.com/capstone-engine/capstone/blob/251c5bb4bc9bb92973e738ae3c5f4ef... [email protected] github.com
github.com/capstone-engine/capstone/security/advisories/GHSA-5m9f-vqcm-g5pr 134c704f-9b21-4f2e-91b3-4a467353bcc0 github.com
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