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CVE-2026-75627 – Unauthenticated Admin Access via Path-Prefix Routing Bypass – Bastillion 0 through

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Summary

CVE-2026-75627 is a critical authentication bypass vulnerability in Bastillion, an open-source SSH key and system management application, affecting versions 0 through 5.1.0. The flaw allows an unauthenticated attacker to reach protected administrative controllers by crafting request URIs that evade the application’s authentication filter, exposing user management and SSH fleet administration functions to remote takeover.

Technical details

  • Root cause: a mismatch between how Bastillion’s AuthFilter and its request dispatcher (BaseKontroller) evaluate the request path — the filter matches against the normalized servlet path for patterns like /manage/* and /admin/*, while the dispatcher originally matched using a substring contains() check against the raw request URI.
  • Trigger condition: an attacker prepends extra path segments (e.g., using matrix parameters such as /x;/manage/viewUsers.ktrl) so the raw URI still contains the protected controller path (satisfying the dispatcher’s substring check) while the normalized servlet path no longer matches /manage/* or /admin/* (causing AuthFilter to skip enforcement).
  • Attack vector: network, no authentication or user interaction required — a single crafted HTTP request against the exposed web interface.
  • Impact: unauthenticated access to administrative controllers, including viewing user listings, creating manager accounts, and registering managed systems, giving an attacker control over SSH access to the managed server fleet.

Affected software

  • Bastillion versions 0 through 5.1.0 (bastillion-io/Bastillion)

Severity

CVSS 3.1 Base Score: 9.8 (Critical) — Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
(IONIX-reported score for this advisory: 9.3)

Mitigation and recommended actions

  • Immediate: upgrade Bastillion to the patched release that enforces exact servlet-path matching (request.getServletPath().equals(...)) between the dispatcher and AuthFilter, rather than substring-based URI matching.
  • If no patch can be applied immediately: restrict network access to the Bastillion management interface (place it behind a VPN or IP allow-list), and deploy a reverse proxy/WAF rule that normalizes and rejects request URIs containing extraneous path segments, matrix parameters (;), or path traversal sequences before they reach the application.
  • Review Bastillion user and managed-system inventories for unexpected accounts or SSH targets that may have been added if the instance was internet-exposed prior to patching.

How IONIX identifies potentially affected assets

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

  • Raw response body: /_res/css/bastillion.css

References

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How IONIX’s External Exposure Management Platform Detects and Validates
Zero-Days to Shrink MTTR

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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  • Confirmation of verified exploitable assets
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