GHSA-8WHX-V8QQ-PQ64

Vulnerability from github – Published: 2026-03-04 20:58 – Updated: 2026-03-06 21:57
VLAI
Summary
changedetection.io has Reflected XSS in its RSS Tag Error Response
Details

A reflected cross-site scripting (XSS) vulnerability was identified in the /rss/tag/ endpoint of changedetection.io. The tag_uuid path parameter is reflected directly in the HTTP response body without HTML escaping. Since Flask returns text/html by default for plain string responses, the browser parses and executes injected JavaScript.

This vulnerability persists in version 0.54.1, which patched the related XSS in /rss/watch/ (CVE-2026-27645 / GHSA-mw8m-398g-h89w) but did not address the identical pattern in the tag RSS endpoint.

Package

  • Ecosystem: pip
  • Package: changedetection.io
  • Affected versions: <= 0.54.1
  • Patched versions: (none yet)

Severity

Moderate - CVSS 6.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

Details

File: changedetectionio/blueprint/rss/tag.py Line: 36 Source: tag.py @ 1d72716

The tag_uuid parameter from the URL path is interpolated into the response body using an f-string with no escaping:

tag = datastore.data['settings']['application'].get('tags', {}).get(tag_uuid)
if not tag:
    return f"Tag with UUID {tag_uuid} not found", 404  # ← No escaping, Content-Type: text/html

Flask's default Content-Type for plain string responses is text/html; charset=utf-8, so any HTML/JavaScript injected via {tag_uuid} is rendered and executed by the browser.

Relationship to CVE-2026-27645

CVE-2026-27645 (GHSA-mw8m-398g-h89w) addressed the identical vulnerability pattern in /rss/watch/ (single_watch.py). The fix applied in v0.54.1 patched that endpoint but did not fix the same pattern in /rss/tag/ (tag.py). Testing confirms:

  • /rss/watch/ on v0.54.1 — Returns generic 404 page, XSS no longer triggers ✅
  • /rss/tag/ on v0.54.1 — XSS payload still fires, vulnerability confirmed ❌

Attack Vector

The attack requires a valid RSS access token, which is a 32-character hex string exposed in the <link> HTML tag on the homepage without authentication:

  1. Attacker visits the target's homepage (if unauthenticated) and extracts the RSS token from the <link> tag

  2. Crafts a malicious URL:

    ``` http://target:5000/rss/tag/?token=EXTRACTED_TOKEN

    ```

  3. Sends the link to a victim who has an active session on the changedetection.io instance

  4. When the victim clicks the link, the server responds with:

    ``` Tag with UUID not found

    ```

  5. The browser renders the <img> tag, the onerror fires, and JavaScript executes in the victim's session context

Proof of Concept

Request

GET /rss/tag/%3Cimg%20src%3Dx%20onerror%3Dalert(document.domain)%3E?token=60b83b06df98b24c66367bc3d233105b HTTP/1.1
Host: localhost:5000

Response

HTTP/1.1 404 NOT FOUND
Content-Type: text/html; charset=utf-8

Tag with UUID <img src=x onerror=alert(document.domain)> not found

The XSS payload is reflected unescaped in an HTML response. The browser executes alert(document.domain) and displays "localhost", confirming JavaScript execution.

Tested on: changedetection.io v0.54.1 (Docker, localhost, Feb 25, 2026)

https://github.com/user-attachments/assets/6db07f6a-6df8-48a7-a597-9f39dfa1bb29

Impact

  • Session cookie theft via document.cookie exfiltration
  • Account takeover if session cookies lack the HttpOnly flag
  • Phishing via crafted links that appear to originate from a trusted changedetection.io instance
  • Low exploitation barrier - the RSS token is obtainable without authentication from the homepage <link> tag
  • Widespread exposure - prior scanning of internet-facing instances (during CVE-2026-27645 research) identified 500+ publicly accessible deployments

Suggested Fix

Escape the tag_uuid parameter before reflecting it in the response, or set the Content-Type to text/plain:

Option A: HTML Escape (Recommended)

from markupsafe import escape

if not tag:
    return f"Tag with UUID {escape(tag_uuid)} not found", 404

Option B: Set Content-Type to text/plain

from flask import make_response

if not tag:
    resp = make_response(f"Tag with UUID {tag_uuid} not found", 404)
    resp.headers['Content-Type'] = 'text/plain; charset=utf-8'
    return resp

Credits

References

Severity
6.1 (Medium)
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
Show details on source website
To clipboard 

{
  "affected": [
    {
      "package": {
        "ecosystem": "PyPI",
        "name": "changedetection.io"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "0.54.4"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-29038"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-79"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-03-04T20:58:14Z",
    "nvd_published_at": "2026-03-06T07:16:01Z",
    "severity": "MODERATE"
  },
  "details": "A reflected cross-site scripting (XSS) vulnerability was identified in the `/rss/tag/` endpoint of changedetection.io. The `tag_uuid` path parameter is reflected directly in the HTTP response body without HTML escaping. Since Flask returns `text/html` by default for plain string responses, the browser parses and executes injected JavaScript.\n\nThis vulnerability persists in version **0.54.1**, which patched the related XSS in `/rss/watch/` (CVE-2026-27645 / GHSA-mw8m-398g-h89w) but did not address the identical pattern in the tag RSS endpoint.\n\n## Package\n\n-   **Ecosystem:** pip\n-   **Package:** changedetection.io\n-   **Affected versions:** \u003c= 0.54.1\n-   **Patched versions:** _(none yet)_\n\n\n## Severity\n**Moderate - CVSS 6.1**\n`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N`\n\n\n## Details\n**File:** `changedetectionio/blueprint/rss/tag.py` **Line:** 36 **Source:** [tag.py @ 1d72716](https://raw.githubusercontent.com/dgtlmoon/changedetection.io/1d72716c6988a4f6796bb85a5d42872800cd7a70/changedetectionio/blueprint/rss/tag.py)\n\nThe `tag_uuid` parameter from the URL path is interpolated into the response body using an f-string with no escaping:\n\n```python\ntag = datastore.data[\u0027settings\u0027][\u0027application\u0027].get(\u0027tags\u0027, {}).get(tag_uuid)\nif not tag:\n    return f\"Tag with UUID {tag_uuid} not found\", 404  # \u2190 No escaping, Content-Type: text/html\n\n```\n\nFlask\u0027s default `Content-Type` for plain string responses is `text/html; charset=utf-8`, so any HTML/JavaScript injected via `{tag_uuid}` is rendered and executed by the browser.\n\n### Relationship to CVE-2026-27645\n\nCVE-2026-27645 (GHSA-mw8m-398g-h89w) addressed the identical vulnerability pattern in `/rss/watch/` (`single_watch.py`). The fix applied in v0.54.1 patched that endpoint but **did not** fix the same pattern in `/rss/tag/` (`tag.py`). Testing confirms:\n\n-   **`/rss/watch/` on v0.54.1** \u2014 Returns generic 404 page, XSS no longer triggers \u2705\n-   **`/rss/tag/` on v0.54.1** \u2014 XSS payload still fires, vulnerability confirmed \u274c\n\n## Attack Vector\n\nThe attack requires a valid RSS access token, which is a 32-character hex string exposed in the `\u003clink\u003e` HTML tag on the homepage without authentication:\n\n1.  Attacker visits the target\u0027s homepage (if unauthenticated) and extracts the RSS token from the `\u003clink\u003e` tag\n2.  Crafts a malicious URL:\n    \n    ```\n    http://target:5000/rss/tag/\u003cimg src=x onerror=alert(document.cookie)\u003e?token=EXTRACTED_TOKEN\n    \n    ```\n    \n3.  Sends the link to a victim who has an active session on the changedetection.io instance\n4.  When the victim clicks the link, the server responds with:\n    \n    ```\n    Tag with UUID \u003cimg src=x onerror=alert(document.cookie)\u003e not found\n    \n    ```\n    \n5.  The browser renders the `\u003cimg\u003e` tag, the `onerror` fires, and JavaScript executes in the victim\u0027s session context\n\n## Proof of Concept\n\n### Request\n\n```http\nGET /rss/tag/%3Cimg%20src%3Dx%20onerror%3Dalert(document.domain)%3E?token=60b83b06df98b24c66367bc3d233105b HTTP/1.1\nHost: localhost:5000\n\n```\n\n### Response\n\n```http\nHTTP/1.1 404 NOT FOUND\nContent-Type: text/html; charset=utf-8\n\nTag with UUID \u003cimg src=x onerror=alert(document.domain)\u003e not found\n\n```\n\nThe XSS payload is reflected unescaped in an HTML response. The browser executes `alert(document.domain)` and displays \"localhost\", confirming JavaScript execution.\n\n**Tested on:** changedetection.io v0.54.1 (Docker, localhost, Feb 25, 2026)\n\n\nhttps://github.com/user-attachments/assets/6db07f6a-6df8-48a7-a597-9f39dfa1bb29\n\n\n## Impact\n\n-   **Session cookie theft** via `document.cookie` exfiltration\n-   **Account takeover** if session cookies lack the `HttpOnly` flag\n-   **Phishing** via crafted links that appear to originate from a trusted changedetection.io instance\n-   **Low exploitation barrier** - the RSS token is obtainable without authentication from the homepage `\u003clink\u003e` tag\n-   **Widespread exposure** - prior scanning of internet-facing instances (during CVE-2026-27645 research) identified 500+ publicly accessible deployments\n\n## Suggested Fix\n\nEscape the `tag_uuid` parameter before reflecting it in the response, or set the `Content-Type` to `text/plain`:\n\n### Option A: HTML Escape (Recommended)\n\n```python\nfrom markupsafe import escape\n\nif not tag:\n    return f\"Tag with UUID {escape(tag_uuid)} not found\", 404\n\n```\n\n### Option B: Set Content-Type to text/plain\n\n```python\nfrom flask import make_response\n\nif not tag:\n    resp = make_response(f\"Tag with UUID {tag_uuid} not found\", 404)\n    resp.headers[\u0027Content-Type\u0027] = \u0027text/plain; charset=utf-8\u0027\n    return resp\n\n```\n## Credits\n\n-   **Roberto Nunes** ([@Akokonunes](https://github.com/Akokonunes)) - Reporter\n-   **neo-ai-engineer** ([@neo-ai-engineer](https://github.com/neo-ai-engineer)) - Reporter\n\n## References\n-   Related advisory: [GHSA-mw8m-398g-h89w](https://github.com/dgtlmoon/changedetection.io/security/advisories/GHSA-mw8m-398g-h89w) (CVE-2026-27645)\n-   Vulnerable source: [tag.py @ 1d72716](https://raw.githubusercontent.com/dgtlmoon/changedetection.io/1d72716c6988a4f6796bb85a5d42872800cd7a70/changedetectionio/blueprint/rss/tag.py)",
  "id": "GHSA-8whx-v8qq-pq64",
  "modified": "2026-03-06T21:57:09Z",
  "published": "2026-03-04T20:58:14Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/dgtlmoon/changedetection.io/security/advisories/GHSA-8whx-v8qq-pq64"
    },
    {
      "type": "WEB",
      "url": "https://github.com/dgtlmoon/changedetection.io/security/advisories/GHSA-mw8m-398g-h89w"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-29038"
    },
    {
      "type": "WEB",
      "url": "https://github.com/dgtlmoon/changedetection.io/commit/ec7d56f85d1e9690fca7cb4711c1fb20dffec780"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/dgtlmoon/changedetection.io"
    },
    {
      "type": "WEB",
      "url": "https://github.com/dgtlmoon/changedetection.io/releases/tag/0.54.4"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "changedetection.io has Reflected XSS in its RSS Tag Error Response"
}



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