Redis Cache Keys tool servers and terminal servers Missing Instance Prefix Enable Cross-Instance Cache Poisoning

Affected Component

• backend/open webui/utils/tools.py (line 841, tool servers SET)
• backend/open webui/utils/tools.py (line 850, tool servers GET)
• backend/open webui/utils/tools.py (line 976, terminal servers SET)
• backend/open webui/utils/tools.py (line 986, terminal servers GET)

Affected Versions

Description

# utils/tools.py — unprefixed keys (problem)
await request.app.state.redis.set('tool servers', ...)    # line 841
json.loads(await request.app.state.redis.get('tool servers')) # line 850
await request.app.state.redis.set('terminal servers', ...)  # line 976
json.loads(await request.app.state.redis.get('terminal servers')) # line 986

# Every other Redis key in the codebase — prefixed (correct pattern)
f'{REDIS KEY PREFIX}:auth:token:{jti}:revoked'
f'{REDIS KEY PREFIX}:ratelimit:{email}:{bucket}'
f'{REDIS KEY PREFIX}:tasks:commands'

Attack Scenario

1. 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).
2. 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.
3. Instance B's users query tools. Instance B reads from tool servers (line 850) — gets Instance A's poisoned list, which now includes the attacker's server alongside or instead of Instance B's legitimate tool servers.
4. Instance B's users invoke tools through the model's context. The attacker's 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.
5. The attacker's server returns arbitrary tool responses, which are fed back into Instance B's LLM context as "trusted tool output" — enabling prompt injection, misinformation delivery, and further data exfiltration cascades.

Impact

• Cross-instance cache poisoning: an admin on one instance affects all users of another instance sharing the Redis backend
• Data exfiltration: tool call payloads contain chat content and user identity, delivered to the attacker's server
• Prompt injection delivery: attacker-returned tool responses enter the victim instance's LLM context as trusted data
• Undermines the multi-instance isolation guarantee that REDIS KEY PREFIX was introduced to provide
• 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

Preconditions

• Multiple Open WebUI instances share a single Redis backend (a supported and documented deployment)
• Attacker has admin access on one of the instances (or escalates to admin via any available path)