# CVE-2026-116733: flatcc through 0.6.4 Out-of-Bounds Read via __flatcc_json_parser_number

Status: published. Published: 2026-10-26. Updated: 2026-11-02.

flatcc through 0.6.4 contains an out-of-bounds read vulnerability in __flatcc_json_parser_number that allows attackers to read past the input buffer via numbers ending in a decimal point. Attackers can supply untrusted JSON ending immediately after a decimal point to generated parsers, crashing applications when the buffer ends at an unmapped page.

## Remediation

- fix: The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches. (source: CNA: VulnCheck) — https://github.com/dvidelabs/flatcc/commit/356792dc155a9e685acdfe0ec1e209bdadcb4ab9

## Affected products and versions

- dvidelabs / flatcc (dvidelabs/flatcc): ≥ 0; ≤ 0.6.4 (affected, custom). Source: CNA: VulnCheck

## Severity and prioritization

- CVSS 4.0: 6.3 (medium); CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N; source: CNA: VulnCheck

- CVSS 3.1: 3.7 (low); CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L; source: CNA: VulnCheck

- CISA KEV: No listing in collected sources

- EPSS: 0.38% as of 2026-11-02; percentile 32.22%

- SSVC: exploitation poc; automatable no; technical impact partial; source ADP: CISA-ADP

- Weaknesses: CWE-125

## Exploit evidence

- exploit: https://hackmd.io/@haindpwn/cve-2026-116733-116734-flatcc-json-number-oob-read (ADP: CISA-ADP)

## References

- https://github.com/dvidelabs/flatcc/commit/356792dc155a9e685acdfe0ec1e209bdadcb4ab9 (CNA: VulnCheck; patch)

- https://github.com/dvidelabs/flatcc (CNA: VulnCheck; product)

- https://github.com/dvidelabs/flatcc/blob/v0.6.4/src/runtime/json_parser.c#L539-L543 (CNA: VulnCheck; technical-description)

- https://hackmd.io/@haindpwn/flatcc-json-number-oob-read (CNA: VulnCheck; third-party-advisory)

- https://www.vulncheck.com/advisories/flatcc-through-0.6.4-out-of-bounds-read-via-flatcc-json-parser-number (CNA: VulnCheck; third-party-advisory)

- https://hackmd.io/@haindpwn/cve-2026-116733-116734-flatcc-json-number-oob-read (ADP: CISA-ADP; exploit)

## Provenance

- CNA: VulnCheck: https://www.cve.org/CVERecord?id=CVE-2026-116733; retrieved 2026-11-02; source updated 2026-11-02

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2026-116733; retrieved 2026-11-02; source updated Not reported

Revision: f06cb5d3a2e7268986f4dbd5629cef1f11bf836e4e65633ec02c194c7cb4818f

Canonical: https://y2.dev/cve/CVE-2026-116733

## Agent and API access

Public CVE pages, Markdown, and JSON are free to read without an account or API key.

- Public catalog: https://y2.dev/cve/index.json. Follow nextCursor with the same search, filters, sort, and limit (1–100). A null cursor marks the end.

- WebMCP: search_cve_disclosures, get_cve_disclosure, get_cve_page_markdown, get_y2_cve_access. Available in compatible browsers.

- Cyber API: https://api.y2.dev/api/v2/cyber/cves and https://api.y2.dev/api/v2/cyber/cves/{cveId}.

- Y2 Pro or Elite: create a workspace API key with the intel:cyber scope and send Authorization: Bearer <Y2_API_KEY>. Setup: https://y2.dev/docs/api/create-key.

- x402: Pay per request without an account or API key. Omit Authorization, read the HTTP 402 PAYMENT-REQUIRED challenge, validate its current requirements, and retry with PAYMENT-SIGNATURE through an authorized payment client. These browser tools never make payments. Guide: https://y2.dev/docs/api/x402.

- OpenAPI: https://y2.dev/api/openapi.yaml. Agent access metadata: https://y2.dev/cve/agent.json.

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