CVE-2026-44558: Open webui Open WebUI's Channel Access Grants Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-7rjh-px4v-5w55",
  "modified" : "2026-05-15T23:52:41Z",
  "published" : "2026-05-08T19:50:51Z",
  "aliases" : [ "CVE-2026-44558" ],
  "summary" : "Open WebUI's Channel Access Grants Bypass filter_allowed_access_grants",
  "details" : "# Channel Access Grants Bypass filter_allowed_access_grants\n\n## Affected Component\n\nChannel creation and update endpoints:\n- `backend/open_webui/routers/channels.py` (lines 291-340, `create_new_channel`)\n- `backend/open_webui/routers/channels.py` (lines 617-638, `update_channel_by_id`)\n- `backend/open_webui/models/channels.py` (lines 825-826, `set_access_grants` call without filtering)\n\n## Affected Versions\n\nCurrent main branch (commit `6fdd19bf1`) and likely all versions supporting user-created group channels with access grants.\n\n## Description\n\nAll resource routers in Open WebUI (knowledge, models, notes, prompts, tools, skills) call `filter_allowed_access_grants()` before persisting access grants. This function strips `principal_id: \"*\"` wildcard grants from users who lack the relevant `sharing.public_*` permission, and strips individual user grants from users who lack `access_grants.allow_users` permission.\n\nThe channel router does not call `filter_allowed_access_grants` on either create or update paths. A non-admin user who can create group channels (or who owns a channel) can submit arbitrary access grants — including public wildcard grants — and those grants are stored verbatim, bypassing the admin's permission framework.\n\n```python\n# channels.py — access_grants from form data flow directly into persistence\n# No call to filter_allowed_access_grants() anywhere in these paths.\n\n# Compare with knowledge.py / models.py / notes.py / prompts.py / tools.py / skills.py,\n# all of which do:\n#     form_data.access_grants = filter_allowed_access_grants(user, form_data.access_grants)\n# before creating or updating.\n```\n\n## Attack Scenario\n\n1. Admin configures permissions so that regular users do NOT have `sharing.public_channels` — public sharing of channels is intended to be admin-only.\n2. Attacker (a regular user) creates or owns a group channel.\n3. Attacker sends:\n   ```\n   POST /api/v1/channels/\n   {\n     \"name\": \"public-channel\",\n     \"type\": \"group\",\n     \"access_control\": {\n       \"access_grants\": [\n         {\"principal_type\": \"user\", \"principal_id\": \"*\", \"permission\": \"read\"}\n       ]\n     }\n   }\n   ```\n4. `set_access_grants` is called directly without `filter_allowed_access_grants` — the wildcard grant is persisted.\n5. The channel becomes publicly readable to every user on the instance, despite the admin's policy prohibiting public channels for regular users.\n\nThe same attack works via `POST /api/v1/channels/{id}/update` for any channel the attacker owns.\n\n## Impact\n\n- Regular users can bypass the `sharing.public_channels` permission and make channels publicly accessible\n- Regular users can bypass `access_grants.allow_users` to grant individual-user access in environments where only group-based sharing is intended\n- Admin's permission framework for channels is silently ineffective\n- Creates an inconsistency with every other resource type in the codebase, making the security posture harder to reason about\n\n## Preconditions\n\n- Attacker must have an account with the ability to create group channels (default user capability), or ownership of an existing channel\n- Admin must have configured restrictive sharing permissions for regular users (otherwise there's no policy to bypass)",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "open-webui"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "0.9.0"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 0.8.12"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/open-webui/open-webui/security/advisories/GHSA-7rjh-px4v-5w55"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-44558"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/open-webui/open-webui"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-862", "CWE-863" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-05-08T19:50:51Z",
    "nvd_published_at" : "2026-05-15T20:16:47Z"
  }
}