CVE-2026-55787 Flyto2 Core: SSRF guard bypass via IPv6 transition addresses (IPv4-mapped / 6to4 / NAT64) in validate_url_ssrf
Authenticated users can bypass SSRF protections using IPv6 transition addresses to access internal services and cloud metadata.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-55787?
CVE-2026-55787 is a high-severity server-side request forgery vulnerability in flytohub flyto-core, published on 14 Oct 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Official 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.
Weakness: CWE-918
Which versions are affected by CVE-2026-55787?
3 open source packages ship an affected version, including flyto-core.
| Package | Affected | Fixed in |
|---|---|---|
flyto-core PyPI | All versions | 2.26.3 |
flyto-core PyPI | All versions | 2.26.3 |
flyto-core PyPI | All versions | 2.26.3 |
How do I fix CVE-2026-55787?
Upgrade flyto-core to 2.26.3 or later.
Upgrade, and send outbound requests through an allow-list that blocks internal addresses. More about Server-side request forgery.
Is CVE-2026-55787 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-55787 exists.
Sources
Also known as GHSA-794r-5rp2-fpg8, PYSEC-2026-2481.