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CVE-2026-63306 – Unauthenticated SSRF – stoatchat (January proxy) before v0.13.5

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Summary

CVE-2026-63306 is a critical, unauthenticated Server-Side Request Forgery (SSRF) vulnerability in stoatchat (formerly Revolt), an open-source self-hosted messaging platform. The flaw resides in the January metadata proxy service, whose /proxy and /embed endpoints accept arbitrary attacker-supplied URLs without DNS resolution filtering or private IP range validation, allowing any unauthenticated network attacker to pivot into the internal network of the host running stoatchat. The vulnerability carries a CVSS 4.0 score of 9.2 (Critical).

Technical details

  • Root cause: The January service — stoatchat’s image and metadata proxy component — exposes /proxy and /embed HTTP endpoints that perform server-side URL fetches on behalf of clients. Neither endpoint validates the supplied URL against a blocklist of private IP ranges (RFC 1918, loopback, link-local) nor applies DNS rebinding protections, meaning any URL resolving to an internal address is fetched without restriction.
  • Trigger conditions: No authentication, no prior access, and no user interaction are required. An attacker sends a single HTTP request containing a crafted URL directly to the publicly reachable January endpoint.
  • Attack vector: Network-accessible; stoatchat instances are designed to be internet-exposed so that community members can connect from anywhere, making the January proxy endpoint reachable from the public internet.
  • Redirect chains: In addition to direct internal IP targeting, attackers can supply URLs that perform server-side redirects to internal addresses, bypassing any shallow URL validation that inspects only the initial request URL.
  • Impact: Successful exploitation enables internal network enumeration, fingerprinting of internal services, and retrieval of cloud instance metadata (e.g., AWS IMDSv1 at 169.254.169.254). Access to the IMDSv1 endpoint can expose temporary cloud credentials, IAM role names, and other sensitive infrastructure data, potentially leading to full cloud account compromise.

Affected software

  • stoatchat — all versions before 0.13.5

Severity

  • CVSS 4.0 Base Score: 9.2 (Critical)
  • Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:H/SI:N/SA:N

Mitigation and recommended actions

  • Immediate action — upgrade: Update stoatchat to v0.13.5 or later, which contains the fix for this vulnerability (released 2026-05-17). Self-hosted operators should update their Docker Compose deployments referencing the stoatchat backend and January service images.
  • Network mitigation (if immediate upgrade is not possible): Restrict inbound access to the /proxy and /embed paths at the reverse proxy or WAF layer so that only trusted, authenticated clients can trigger outbound fetches. Block or rate-limit requests originating from untrusted sources to the January service endpoint.
  • Cloud environment hardening: If the vulnerable stoatchat instance runs in a cloud environment, enforce IMDSv2 (token-required mode) on all cloud instances to prevent unauthenticated metadata retrieval even if SSRF is achieved.

IONIX Status

The IONIX research team is tracking ongoing exploitation attempts and recommends immediate patching. Potentially affected assets are outlined in this post.

References

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Map your entire attack surface (continously)

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