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CVE-2026-55245 – SSRF via Incomplete IP Deny-List – Bifrost AI Gateway < 1.5.17

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Summary

CVE-2026-55245 is a Server-Side Request Forgery (SSRF) vulnerability in Bifrost, an AI gateway used to route requests to model providers. The flaw lies in the isPublicIP validation function used to filter outbound URLs for multimodal (image/document) requests, and it fails to block several routable address ranges that can resolve to internal or cloud-metadata infrastructure. The issue is rated HIGH severity with a CVSS v4.0 base score of 8.7.

Technical details

  • Root cause: the isPublicIP function in core/providers/utils/fetch.go relies on addr.IsPrivate() and Unmap(), which do not account for Carrier-Grade NAT (100.64.0.0/10), IPv6 6to4 (2002::/16) and NAT64 (64:ff9b::/96, 64:ff9b:1::/48) embedded addresses, or deprecated IPv6 site-local addresses (fec0::/10).
  • Trigger condition: a client supplies a URL for a multimodal (image/document) request that is processed by FetchAndEncodeURL, used by the Bedrock and Vertex provider integrations.
  • Attack vector: network, no authentication or user interaction required; an attacker controls the fetched URL and encodes a disallowed address inside an allowed representation (e.g., 6to4/NAT64 encodings of 169.254.169.254).
  • Impact: the gateway can be coerced into fetching internal network resources or cloud instance metadata endpoints, potentially exposing sensitive internal data or credentials.

Affected software

  • Bifrost Core versions ≤ 1.5.15 (fixed in 1.5.16 and later)

Severity

  • CVSS v4.0 Base Score: 8.7 (HIGH)
  • Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N

Mitigation and recommended actions

  • Immediate: Upgrade Bifrost Core to version 1.5.16 or later, which adds explicit checks for CGNAT ranges, validates embedded IPv4 addresses extracted from 6to4/NAT64 representations, and rejects deprecated site-local addressing.
  • If immediate patching is not possible: restrict outbound network access from the Bifrost gateway to internal/private address ranges and cloud metadata endpoints at the network or firewall layer, and disable or closely monitor multimodal (image/document URL) request handling for Bedrock/Vertex providers until patched.

How IONIX identifies potentially affected assets

IONIX matches the following signals against data already collected when it crawled the asset; identifying the technology sends no request beyond that crawl.

  • Raw response body: id="bifrost-shell", src="bifrost-logo.webp", src="bifrost-logo-dark.webp"

References

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1

Map your entire attack surface (continously)

IONIX uses multi-factor discovery methods, including DNS analysis, certificate mapping, metadata inspection, and more, to automatically map every internet-facing asset across your environment. This includes cloud instances, third-party platforms, shadow IT, and even forgotten infrastructure that traditional tools miss.

2

Monitor for new CVEs

Dozens of threat intel feeds using agentic technology are continuously analyzed to detect the appearance of proof-of-concept code, exploit kits, and indicators of active targeting. IONIX goes further by applying AI to proactively evaluate whether emerging vulnerabilities are likely to be exploited, even before PoCs go public.

3

Identify Potential External Exposures

Not all CVEs matter. IONIX filters vulnerabilities by asking attacker-centric questions: Can it be reached from the internet? Does it require authentication? Is it being exploited in the wild? This dramatically reduces noise and focuses teams on threats that can actually be weaponized.

4

Create Safe, Scalable Exploit Validations

IONIX transforms real-world PoCs into safe, non-intrusive test payloads that can be run in production environments without disruption. These simulations are precisely targeted to the systems that are vulnerable, ensuring rapid validation without unnecessary load.

5

Execute Exploit Validations

By combining context about software stack, versioning, exposure status, and reachability, IONIX ensures that only the right payloads are executed against the right assets, maximizing efficiency and minimizing risk.

6

Drive Fast and Actionable Remediation

Results are routed through integrations with ticketing, SOAR, and SIEM tools. Issues are written in plain language, bundled into remediation clusters, and prioritized based on asset criticality, exploitability, and blast radius. This shortens mean time to remediation (MTTR) and empowers teams to act with confidence.

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