{"id":"CVE-2026-44558","aliases":["GHSA-7rjh-px4v-5w55","PYSEC-2026-2711"],"url":"https://o3.security/vulnerability/CVE-2026-44558","summary":"Open WebUI: 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)","published":"2026-05-15T19:43:40.120Z","modified":"2026-08-12T03:51:10.035105503Z","cvss":{"score":5.4,"severity":"MEDIUM","vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N"},"epss":{"score":0.0019,"percentile":0.08686,"asOf":"2026-08-24"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"PyPI","name":"open-webui","fixedVersion":"0.9.0"}],"fix":null,"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/44xxx/CVE-2026-44558.json"},{"type":"ADVISORY","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"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-12T03:51:10.035105503Z"}}