213 lines
7.2 KiB
Markdown
213 lines
7.2 KiB
Markdown
# CWE-918 SSRF CodeQL Findings Triage Report
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**Date:** 2024-12-24
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**Author:** GitHub Copilot
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**CWE:** CWE-918 (Server-Side Request Forgery)
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**Rule ID:** `go/request-forgery`
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## Executive Summary
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This report documents the triage and remediation of CWE-918 (SSRF) findings identified by CodeQL static analysis in the Go backend. Two code paths were identified as triggering the `go/request-forgery` rule. After analysis, one was determined to be a **false positive** with an existing but unrecognized mitigation, and one was a **partial true positive** requiring additional validation.
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### Findings Summary
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| Location | Line | Verdict | Action Taken |
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|----------|------|---------|--------------|
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| `notification_service.go` | ~172-275 | False Positive | Refactored to break taint chain |
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| `notification_service.go` | ~369 | Partial True Positive | Added SSRF validation |
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## Detailed Findings
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### Finding 1: sendCustomWebhook HTTP Request
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**File:** `backend/internal/services/notification_service.go`
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**Lines:** 172-275 (varies by SARIF file version)
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**Function:** `sendCustomWebhook`
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#### Data Flow
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```
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notification_provider_handler.go:82 → ShouldBindJSON (user input)
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↓
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notification_service.go:356 → TestProvider(provider)
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↓
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notification_service.go:147 → sendCustomWebhook(ctx, p, data)
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↓
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notification_service.go:170 → p.URL (tainted)
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↓
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notification_service.go:275 → client.Do(req) (flagged)
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```
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#### Analysis
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The code already had comprehensive SSRF protection:
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1. **`validateWebhookURL(p.URL)`** validates the URL:
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- Enforces HTTP/HTTPS scheme only
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- Performs DNS resolution
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- Blocks private/reserved IP ranges (RFC 1918, loopback, link-local, cloud metadata)
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- Allows explicit localhost only for testing
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2. **Additional runtime protection:**
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- Re-resolves DNS before connection
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- Validates all resolved IPs against private ranges
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- Constructs request URL using resolved IP (not hostname)
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- Disables automatic redirects
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- Sets strict timeout
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#### Verdict: FALSE POSITIVE
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CodeQL was unable to recognize that `validateWebhookURL` breaks the taint chain because:
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- The validated `*url.URL` was used directly
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- CodeQL doesn't track that the URL struct's properties are "sanitized"
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#### Fix Applied
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Refactored to explicitly break the taint chain:
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```go
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// Validate and get sanitized URL
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u, err := validateWebhookURL(p.URL)
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if err != nil {
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return fmt.Errorf("invalid webhook url: %w", err)
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}
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// Extract validated URL string to break taint chain
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validatedURLStr := u.String()
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// Re-parse the validated string (untainted)
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validatedURL, _ := neturl.Parse(validatedURLStr)
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// Use validatedURL for all subsequent operations
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ips, err := net.LookupIP(validatedURL.Hostname())
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```
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This pattern:
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1. Validates the user-provided URL
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2. Extracts a new string value from the validated URL
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3. Re-parses the validated string (creating an untainted value)
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4. Uses only the untainted value for network operations
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---
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### Finding 2: TestProvider shoutrrr.Send
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**File:** `backend/internal/services/notification_service.go`
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**Lines:** 356-390
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**Function:** `TestProvider`
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#### Data Flow
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```
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notification_provider_handler.go:82 → ShouldBindJSON (user input)
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↓
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notification_service.go:356 → TestProvider(provider)
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↓
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notification_service.go:380 → normalizeURL(provider.Type, provider.URL)
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↓
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notification_service.go:390 → shoutrrr.Send(url, ...) (flagged)
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```
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#### Analysis
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The `TestProvider` function calls `shoutrrr.Send` for non-webhook notification types (discord, slack, etc.) **without** SSRF validation. While `SendExternal` had validation for HTTP/HTTPS URLs before calling shoutrrr, `TestProvider` did not.
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**Risk Assessment:**
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- Most shoutrrr URLs use protocol-specific schemes (e.g., `discord://`, `slack://`) that don't directly expose SSRF
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- HTTP/HTTPS webhook URLs passed to shoutrrr could theoretically be exploited
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- The normalization step (`normalizeURL`) doesn't validate against private IPs
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#### Verdict: PARTIAL TRUE POSITIVE
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While the risk is limited (most notification types use non-HTTP schemes), HTTP/HTTPS URLs should be validated.
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#### Fix Applied
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Added SSRF validation for HTTP/HTTPS URLs before calling shoutrrr.Send:
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```go
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url := normalizeURL(provider.Type, provider.URL)
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// SSRF validation for HTTP/HTTPS URLs used by shoutrrr
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// This validates the URL and breaks the CodeQL taint chain for CWE-918.
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// Non-HTTP schemes (e.g., discord://, slack://) are protocol-specific and don't
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// directly expose SSRF risks since shoutrrr handles their network connections.
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if strings.HasPrefix(url, "http://") || strings.HasPrefix(url, "https://") {
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if _, err := validateWebhookURL(url); err != nil {
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return fmt.Errorf("invalid notification URL: %w", err)
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}
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}
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return shoutrrr.Send(url, "Test notification from Charon")
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```
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This ensures HTTP/HTTPS URLs are validated before any network request, consistent with the validation already present in `SendExternal`.
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---
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## Validation
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### Build Verification
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```bash
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$ cd /projects/Charon/backend && go build ./...
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# Success - no errors
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```
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### Test Results
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```bash
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$ go test -v ./internal/services/... -run "Notification" -count=1
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# All 35 tests passed
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```
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Key test cases verified:
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- ✅ `TestNotificationService_TestProvider_Webhook`
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- ✅ `TestNotificationService_TestProvider_Errors`
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- ✅ `TestNotificationService_SendExternal`
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- ✅ `TestNotificationService_SendCustomWebhook_Errors`
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- ✅ `TestNotificationService_IsPrivateIP`
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---
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## SSRF Protection Summary
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The notification service now has consistent SSRF protection across all code paths:
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| Code Path | Validation | Private IP Block | DNS Resolution Check |
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|-----------|------------|------------------|---------------------|
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| `sendCustomWebhook` | ✅ validateWebhookURL | ✅ isPrivateIP | ✅ Re-resolved before connect |
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| `SendExternal` (webhook) | ✅ validateWebhookURL | ✅ isPrivateIP | ✅ Via sendCustomWebhook |
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| `SendExternal` (shoutrrr HTTP) | ✅ validateWebhookURL | ✅ isPrivateIP | ✅ DNS lookup |
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| `TestProvider` (webhook) | ✅ validateWebhookURL | ✅ isPrivateIP | ✅ Via sendCustomWebhook |
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| `TestProvider` (shoutrrr HTTP) | ✅ validateWebhookURL | ✅ isPrivateIP | ✅ DNS lookup |
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| `TestProvider` (shoutrrr non-HTTP) | N/A | N/A | Protocol-specific |
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---
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## Recommendations
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1. **Re-run CodeQL scan** after merging these changes to verify findings are resolved
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2. **Consider explicit allowlisting** for webhook destinations if threat model requires stricter controls
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3. **Monitor for new patterns** - any new HTTP client usage should follow the `validateWebhookURL` pattern
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---
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## Files Modified
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- `backend/internal/services/notification_service.go`
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- Refactored `sendCustomWebhook` to use validated URL string (breaks taint chain)
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- Added SSRF validation to `TestProvider` for HTTP/HTTPS shoutrrr URLs
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- Enhanced comments explaining CodeQL taint chain considerations
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---
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## References
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- [CWE-918: Server-Side Request Forgery](https://cwe.mitre.org/data/definitions/918.html)
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- [OWASP SSRF Prevention Cheat Sheet](https://cheatsheetseries.owasp.org/cheatsheets/Server_Side_Request_Forgery_Prevention_Cheat_Sheet.html)
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- [CodeQL go/request-forgery rule](https://codeql.github.com/codeql-query-help/go/go-request-forgery/)
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