Redis Cache Keys tool_servers and terminal_servers Missing Instance Prefix Enable Cross-Instance Cache Poisoning

{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 0.8.12"
      },
      "package": {
        "ecosystem": "PyPI",
        "name": "open-webui"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "0.9.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-44552"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-668"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-05-08T19:44:40Z",
    "nvd_published_at": "2026-05-15T20:16:46Z",
    "severity": "HIGH"
  },
  "details": "# Redis Cache Keys tool_servers and terminal_servers Missing Instance Prefix Enable Cross-Instance Cache Poisoning\n\n## Affected Component\n\nTool server and terminal server Redis cache:\n- `backend/open_webui/utils/tools.py` (line 841, tool_servers SET)\n- `backend/open_webui/utils/tools.py` (line 850, tool_servers GET)\n- `backend/open_webui/utils/tools.py` (line 976, terminal_servers SET)\n- `backend/open_webui/utils/tools.py` (line 986, terminal_servers GET)\n\n## Affected Versions\n\nCurrent main branch (commit `6fdd19bf1`) and likely all versions since the tool server / terminal server Redis cache was introduced.\n\n## Description\n\nOpen WebUI uses a `REDIS_KEY_PREFIX` (default `open-webui`) to namespace Redis keys, allowing multiple instances to safely share a single Redis backend. Every Redis key in the codebase uses this prefix \u2014 except the `tool_servers` and `terminal_servers` keys in `utils/tools.py`, which use bare key names.\n\nWhen two or more Open WebUI instances share a Redis database (a supported and documented deployment pattern, e.g., for multi-region deployments, blue-green setups, or cluster topologies), the unprefixed keys collide. An admin on Instance A writing to `tool_servers` overwrites the value read by Instance B \u2014 causing Instance B\u0027s users to receive Instance A\u0027s tool server configuration.\n\n```python\n# utils/tools.py \u2014 unprefixed keys (problem)\nawait request.app.state.redis.set(\u0027tool_servers\u0027, ...)        # line 841\njson.loads(await request.app.state.redis.get(\u0027tool_servers\u0027)) # line 850\nawait request.app.state.redis.set(\u0027terminal_servers\u0027, ...)    # line 976\njson.loads(await request.app.state.redis.get(\u0027terminal_servers\u0027))  # line 986\n\n# Every other Redis key in the codebase \u2014 prefixed (correct pattern)\nf\u0027{REDIS_KEY_PREFIX}:auth:token:{jti}:revoked\u0027\nf\u0027{REDIS_KEY_PREFIX}:ratelimit:{email}:{bucket}\u0027\nf\u0027{REDIS_KEY_PREFIX}:tasks:commands\u0027\n```\n\n## Attack Scenario\n\nTwo Open WebUI instances (A and B) share a Redis backend \u2014 a supported deployment for multi-region setups, blue-green deployments, or hot-standby. Both instances have their own admin accounts; the shared Redis was chosen for coordinated session handling, rate limiting, and task management.\n\n1. Attacker is an admin on Instance A (a legitimately provisioned admin, or one that escalated via any available path including the LDAP empty-password or stale-admin-role findings).\n2. Attacker on Instance A configures a tool server pointing to `https://attacker-controlled.example.com/openapi.json`. This triggers `utils/tools.py:841` to write the new tool server list under the bare key `tool_servers`.\n3. Instance B\u0027s users query tools. Instance B reads from `tool_servers` (line 850) \u2014 gets Instance A\u0027s poisoned list, which now includes the attacker\u0027s server alongside or instead of Instance B\u0027s legitimate tool servers.\n4. Instance B\u0027s users invoke tools through the model\u0027s context. The attacker\u0027s server receives tool call payloads containing: chat content, user identity, OAuth tokens scoped to the tool server (if the user has bound their external account), and in-flight conversation context.\n5. The attacker\u0027s server returns arbitrary tool responses, which are fed back into Instance B\u0027s LLM context as \"trusted tool output\" \u2014 enabling prompt injection, misinformation delivery, and further data exfiltration cascades.\n\nThe same cross-instance poisoning applies to `terminal_servers`.\n\n## Impact\n\n- Cross-instance cache poisoning: an admin on one instance affects all users of another instance sharing the Redis backend\n- Data exfiltration: tool call payloads contain chat content and user identity, delivered to the attacker\u0027s server\n- Prompt injection delivery: attacker-returned tool responses enter the victim instance\u0027s LLM context as trusted data\n- Undermines the multi-instance isolation guarantee that `REDIS_KEY_PREFIX` was introduced to provide\n- Silent failure mode: no error is raised; the victim instance sees a valid, signed cache entry and has no way to detect it came from a different instance\n\n## Preconditions\n\n- Multiple Open WebUI instances share a single Redis backend (a supported and documented deployment)\n- Attacker has admin access on one of the instances (or escalates to admin via any available path)",
  "id": "GHSA-3x8w-4f7p-xxc2",
  "modified": "2026-05-15T23:52:27Z",
  "published": "2026-05-08T19:44:40Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/open-webui/open-webui/security/advisories/GHSA-3x8w-4f7p-xxc2"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-44552"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/open-webui/open-webui"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Open WebUI: Redis Cache Keys tool_servers and terminal_servers Missing Instance Prefix Enable Cross-Instance Cache Poisoning"
}