GHSA-4c3j-3h7v-22q9 changedetection.io: Stored XSS in Watch update via API

• PyPI changedetection.io: < 0.50.34 → fixed in 0.50.34

Summary A Stored Cross Site Scripting is present in the changedetection.io Watch update API due to unsufficient security checks. Details Tested on changedetection.io version *v0.50.24* ```console REPOSITORY TAG IMAGE ID CREATED SIZE ghcr.io/dgtlmoon/changedetection.io latest 0367276509a0 23 hours ago 599MB ``` When a user tries to add an unsafe URL as a Watch in the changedetection.io UI, the action is blocked with the error message "Watch protocol is not permitted by SAFE_PROTOCOL_REGEX or incorrect URL format". This is catched by the function `validate_url(test_url)`. ```python def validate_url(test_url): # ... from .model.Watch import is_safe_url if not is_safe_url(test_url): # This should be wtforms.validators. raise ValidationError('Watch protocol is not permitted by SAFE_PROTOCOL_REGEX or incorrect URL format') ``` When instead the Watch API is used, this check is not performed resulting in unsafe URLs added as Watch. PoC Update an existing watch with an unsafe URL ```console curl -X PUT "http://example.site/api/v1/watch/1242e1c5-d59e-4352-0078-203a55b21282" \ -H "x-api-key: XXX" \ -H "Content-Type: application/json" \ -d '{ "url": "javascript:alert(document.domain)", "title": "XSS PoC", "paused": false }' ``` Impact Two scenarios are possibile: 1. An attacker can insert a new watch with an arbitrary URL which really points to a web page. Once the HTML content is retrieved, the attacker updates the URL with a JavaScript payload. 2. An attacker substitutes the URL in an existing watch with a new URL that is in reality a JavaScript payload. When the user clicks on *Preview* and then on the malicious link, the JavaScript malicious code is executed. Credits Edoardo Ottavianelli @edoardottt