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CVE-2026-100676 – Local Filesystem Read / DoS via SVG Proxy – stoatchat before 0.15.5

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Summary

CVE-2026-100676 is a protection mechanism failure (CWE-693) in stoatchat’s media proxy/embed service ("January") affecting all versions before 0.15.5. When a proxied resource is served as image/svg+xml, the service improperly resolves <image href> values inside the SVG as local filesystem paths, allowing an unauthenticated remote attacker to probe for file existence, disclose local image files, and trigger unbounded disk I/O. The issue carries a HIGH severity rating.

Technical details

  • Root cause: The SVG rendering/re-encoding logic in stoatchat’s proxy service treats <image href> attributes in attacker-supplied SVG content as local filesystem paths instead of restricting resolution to remote/embedded resources.
  • Trigger conditions: An attacker hosts a crafted SVG file and causes the stoatchat proxy (e.g., the /proxy endpoint) to fetch and process it as image/svg+xml.
  • Attack vector: Network, unauthenticated, no user interaction required (CVSS v4.0 AV:N/AC:L/AT:N/PR:N/UI:N).
  • Impact:
    • File-existence detection via observable response-time differences.
    • Disclosure of local image file contents after re-encoding.
    • Denial of service through unbounded filesystem I/O and memory pressure — the published proof of concept generates approximately 4.34 GB of reads from a single request.

Affected software

  • stoatchat/stoatchat — all versions prior to 0.15.5
  • Fixed in version 0.15.5 and later

Severity

  • CVSS v4.0 Base Score: 8.8 (HIGH) — CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:N/VA:H/SC:N/SI:N/SA:N
  • CVSS v3.1 Base Score: 8.2 (HIGH) — CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H

Mitigation and recommended actions

  • Immediate: Upgrade stoatchat to version 0.15.5 or later, which fixes the SVG path-resolution issue.
  • If no patch can be applied immediately: Restrict or disable the media proxy/embed (/proxy) functionality for untrusted or external content, block SVG content types from being proxied/re-encoded, and monitor for unusual outbound proxy requests or abnormal response-time patterns that could indicate file-existence probing.

References

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