flyto-core has SSRF guard bypass via IPv6 transition addresses (IPv4-mapped / 6to4 / NAT64) in validate_url_ssrf

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

7.1 · CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:L/A:N

EPSS

• CVE-2026-55787: 0.29% estimated exploitation activity in the next 30 days; percentile 21.86 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary flyto-core's SSRF protection (validateurlssrf / isprivateip in src/core/utils.py) blocks private and metadata destinations by resolving the host and testing the resulting IP for membership in a hardcoded PRIVATEIPRANGES list. That list contains only the native RFC 1918 / loopback / link-local / unique-local ranges. It does not account for IPv6 transition address forms that embed an IPv4 (or loopback) target: - IPv4-mapped ::ffff:a.b.c.d - IPv4-compatible ::a.b.c.d - 6to4 2002::/16 - NAT64 well-known prefix 64:ff9b::/96 and local-use 64:ff9b:1::/48 A workflow author can submit a URL with a literal transition-form host (for example http://[::ffff:127.0.0.1]:8080/... or http://[64:ff9b::a9fe:a9fe]/latest/meta-data/). isprivateip() returns False for these (the address is not literally inside any listed range), so validateurlssrf lets the request through, and the http.get atomic module (and ~10 sibling modules that share the same guard) performs the outbound aiohttp fetch and…

Published by the source

6 Jul 2026, 17:30 UTC

Last modified by the source

13 Jul 2026, 16:42 UTC

Source last checked

26 Oct 2026, 13:46 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-794r-5rp2-fpg8

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-794r-5rp2-fpg8

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# Patch Next advisory brief: CVE-2026-55787

Advisory: flyto-core has SSRF guard bypass via IPv6 transition addresses (IPv4-mapped / 6to4 / NAT64) in validate_url_ssrf
IDs: CVE-2026-55787, GHSA-794r-5rp2-fpg8
Record: https://patchnext.com/advisories/cve-2026-55787 (revision 2, source checked 26 Oct 2026, 13:46 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.1)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: flyto-core 2.26.3. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI flyto-core: affected <= 2.26.2; fixed in 2.26.3

## Suggested inspection (read-only)
- `python -m pip show flyto-core`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on flyto-core.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-794r-5rp2-fpg8 (OSV record GHSA-794r-5rp2-fpg8 lists affected ranges: PyPI flyto-core >=0 <2.26.3 (fixed))
- Verified: https://github.com/advisories/GHSA-794r-5rp2-fpg8 (GitHub-reviewed advisory GHSA-794r-5rp2-fpg8 lists affected ranges: PyPI flyto-core >=0 <=2.26.2)

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