CVE-2026-54015

Open WebUI is a self-hosted artificial intelligence platform designed to operate entirely offline. Prior to 0.9.6, Open WebUI's prompt version-history endpoints authorize the prompt_id in the URL but then act on caller-supplied history IDs without verifying that the history row belongs to that prompt (history_entry.prompt_id == prompt.id). This affects /api/v1/prompts/id/{prompt_id}/history/diff, /api/v1/prompts/id/{prompt_id}/update/version, and /api/v1/prompts/id/{prompt_id}/history/{history_id}. An authenticated user with access to any prompt they control, plus a victim prompt_history.id, can read or delete another user's private prompt history. This vulnerability is fixed in 0.9.6.

Open WebUI is a self-hosted artificial intelligence platform designed to operate entirely offline. Prior to 0.9.6, Open WebUI's prompt version-history endpoints authorize the prompt_id in the URL but then act on caller-supplied history IDs without verifying that the history row belongs to that prompt (history_entry.prompt_id == prompt.id). This affects /api/v1/prompts/id/{prompt_id}/history/diff, /api/v1/prompts/id/{prompt_id}/update/version, and /api/v1/prompts/id/{prompt_id}/history/{history_id}. An authenticated user with access to any prompt they control, plus a victim prompt_history.id, can read or delete another user's private prompt history. This vulnerability is fixed in 0.9.6.

Summary

Open WebUI's prompt version-history endpoints authorize the prompt_id in the URL but then act on caller-supplied history IDs without verifying that the history row belongs to that prompt (history_entry.prompt_id == prompt.id). Three operations are affected:

• GET /api/v1/prompts/id/{prompt_id}/history/diff — returns another prompt's history snapshots (read).
• POST /api/v1/prompts/id/{prompt_id}/update/version — restores another prompt's snapshot into the caller's prompt, exposing its content (read).
• DELETE /api/v1/prompts/id/{prompt_id}/history/{history_id} — deletes another prompt's history entry (delete).

An authenticated user with access to any prompt they control, plus a victim prompt_history.id, can read or delete another user's private prompt history. The single-entry read endpoint (GET .../history/{history_id}) already enforces the binding; these three did not.

Impact

Security boundary crossed: prompt confidentiality and integrity.

Prompt history snapshots can contain private prompt text, internal instructions, and sensitive variables. With a known victim prompt_history.id, an attacker can read another user's snapshot (via the diff endpoint or by restoring it into their own prompt) and delete another user's history entry. The active prompt row is not destroyed; the delete impact is against version history. Exploitation requires knowing or obtaining victim history UUIDs, so severity depends on adjacent ID exposure.

Root Cause

The route checks read access only for prompt_id:

# backend/open_webui/routers/prompts.py
prompt = await Prompts.get_prompt_by_id(prompt_id, db=db)
...
if not (
    user.role == 'admin'
    or prompt.user_id == user.id
    or await AccessGrants.has_access(
        user_id=user.id,
        resource_type='prompt',
        resource_id=prompt.id,
        permission='read',
        db=db,
    )
):
    raise HTTPException(...)

But the authorized prompt ID is not passed into the diff sink:

# backend/open_webui/routers/prompts.py
diff = await PromptHistories.compute_diff(from_id, to_id, db=db)

compute_diff() fetches both history entries globally by ID and returns their full snapshots:

# backend/open_webui/models/prompt_history.py
result_from = await db.execute(select(PromptHistory).filter(PromptHistory.id == from_id))
from_entry = result_from.scalars().first()
result_to = await db.execute(select(PromptHistory).filter(PromptHistory.id == to_id))
to_entry = result_to.scalars().first()
...
return {
    'from_snapshot': from_snapshot,
    'to_snapshot': to_snapshot,
    ...
}

There is no check that from_entry.prompt_id == prompt_id or to_entry.prompt_id == prompt_id.

The same missing binding affects two further endpoints. POST .../update/version restores a snapshot fetched globally by version_id:

# backend/open_webui/models/prompts.py — update_prompt_version
history_entry = await PromptHistories.get_history_entry_by_id(version_id, db=session)
...
prompt.content = snapshot.get('content', prompt.content)   # foreign snapshot copied into caller's prompt
prompt.version_id = version_id

DELETE .../history/{history_id} deletes an entry fetched globally by history_id:

# backend/open_webui/models/prompt_history.py — delete_history_entry
result = await db.execute(select(PromptHistory).filter_by(id=history_id))
entry = result.scalars().first()
...
await db.delete(entry)

Neither checks entry.prompt_id == prompt.id. The single-entry read endpoint (GET .../history/{history_id}) does (history_entry.prompt_id != prompt.id → 404); these three endpoints were missing it.

PoC

#!/usr/bin/env python3
"""
PoC for prompt history diff IDOR.

The PoC executes:
  - the real routers.prompts.get_prompt_diff() route function
  - the real PromptHistories.compute_diff() implementation

Fake model/DB adapters are used only to avoid requiring a running server. The…

Open WebUI is a self-hosted artificial intelligence platform designed to operate entirely offline. Prior to 0.9.6, Open WebUI's prompt version-history endpoints authorize the prompt_id in the URL but then act on caller-supplied history IDs without verifying that the history row belongs to that prompt (history_entry.prompt_id == prompt.id). This affects /api/v1/prompts/id/{prompt_id}/history/diff, /api/v1/prompts/id/{prompt_id}/update/version, and /api/v1/prompts/id/{prompt_id}/history/{history_id}. An authenticated user with access to any prompt they control, plus a victim prompt_history.id, can read or delete another user's private prompt history. This vulnerability is fixed in 0.9.6.

Open WebUI is a self-hosted artificial intelligence platform designed to operate entirely offline. Prior to 0.9.6, Open WebUI's prompt version-history endpoints authorize the prompt_id in the URL but then act on caller-supplied history IDs without verifying that the history row belongs to that prompt (history_entry.prompt_id == prompt.id). This affects /api/v1/prompts/id/{prompt_id}/history/diff, /api/v1/prompts/id/{prompt_id}/update/version, and /api/v1/prompts/id/{prompt_id}/history/{history_id}. An authenticated user with access to any prompt they control, plus a victim prompt_history.id, can read or delete another user's private prompt history. This vulnerability is fixed in 0.9.6.

Summary

Open WebUI's prompt version-history endpoints authorize the prompt_id in the URL but then act on caller-supplied history IDs without verifying that the history row belongs to that prompt (history_entry.prompt_id == prompt.id). Three operations are affected:

• GET /api/v1/prompts/id/{prompt_id}/history/diff — returns another prompt's history snapshots (read).
• POST /api/v1/prompts/id/{prompt_id}/update/version — restores another prompt's snapshot into the caller's prompt, exposing its content (read).
• DELETE /api/v1/prompts/id/{prompt_id}/history/{history_id} — deletes another prompt's history entry (delete).

An authenticated user with access to any prompt they control, plus a victim prompt_history.id, can read or delete another user's private prompt history. The single-entry read endpoint (GET .../history/{history_id}) already enforces the binding; these three did not.

Impact

Security boundary crossed: prompt confidentiality and integrity.

Prompt history snapshots can contain private prompt text, internal instructions, and sensitive variables. With a known victim prompt_history.id, an attacker can read another user's snapshot (via the diff endpoint or by restoring it into their own prompt) and delete another user's history entry. The active prompt row is not destroyed; the delete impact is against version history. Exploitation requires knowing or obtaining victim history UUIDs, so severity depends on adjacent ID exposure.

Root Cause

The route checks read access only for prompt_id:

# backend/open_webui/routers/prompts.py
prompt = await Prompts.get_prompt_by_id(prompt_id, db=db)
...
if not (
    user.role == 'admin'
    or prompt.user_id == user.id
    or await AccessGrants.has_access(
        user_id=user.id,
        resource_type='prompt',
        resource_id=prompt.id,
        permission='read',
        db=db,
    )
):
    raise HTTPException(...)

But the authorized prompt ID is not passed into the diff sink:

# backend/open_webui/routers/prompts.py
diff = await PromptHistories.compute_diff(from_id, to_id, db=db)

compute_diff() fetches both history entries globally by ID and returns their full snapshots:

# backend/open_webui/models/prompt_history.py
result_from = await db.execute(select(PromptHistory).filter(PromptHistory.id == from_id))
from_entry = result_from.scalars().first()
result_to = await db.execute(select(PromptHistory).filter(PromptHistory.id == to_id))
to_entry = result_to.scalars().first()
...
return {
    'from_snapshot': from_snapshot,
    'to_snapshot': to_snapshot,
    ...
}

There is no check that from_entry.prompt_id == prompt_id or to_entry.prompt_id == prompt_id.

The same missing binding affects two further endpoints. POST .../update/version restores a snapshot fetched globally by version_id:

# backend/open_webui/models/prompts.py — update_prompt_version
history_entry = await PromptHistories.get_history_entry_by_id(version_id, db=session)
...
prompt.content = snapshot.get('content', prompt.content)   # foreign snapshot copied into caller's prompt
prompt.version_id = version_id

DELETE .../history/{history_id} deletes an entry fetched globally by history_id:

# backend/open_webui/models/prompt_history.py — delete_history_entry
result = await db.execute(select(PromptHistory).filter_by(id=history_id))
entry = result.scalars().first()
...
await db.delete(entry)

Neither checks entry.prompt_id == prompt.id. The single-entry read endpoint (GET .../history/{history_id}) does (history_entry.prompt_id != prompt.id → 404); these three endpoints were missing it.

PoC

#!/usr/bin/env python3
"""
PoC for prompt history diff IDOR.

The PoC executes:
  - the real routers.prompts.get_prompt_diff() route function
  - the real PromptHistories.compute_diff() implementation

Fake model/DB adapters are used only to avoid requiring a running server. The…

Summary

Open WebUI's prompt version-history endpoints authorize the prompt_id in the URL but then act on caller-supplied history IDs without verifying that the history row belongs to that prompt (history_entry.prompt_id == prompt.id). Three operations are affected:

• GET /api/v1/prompts/id/{prompt_id}/history/diff — returns another prompt's history snapshots (read).
• POST /api/v1/prompts/id/{prompt_id}/update/version — restores another prompt's snapshot into the caller's prompt, exposing its content (read).
• DELETE /api/v1/prompts/id/{prompt_id}/history/{history_id} — deletes another prompt's history entry (delete).

An authenticated user with access to any prompt they control, plus a victim prompt_history.id, can read or delete another user's private prompt history. The single-entry read endpoint (GET .../history/{history_id}) already enforces the binding; these three did not.

Impact

Security boundary crossed: prompt confidentiality and integrity.

Prompt history snapshots can contain private prompt text, internal instructions, and sensitive variables. With a known victim prompt_history.id, an attacker can read another user's snapshot (via the diff endpoint or by restoring it into their own prompt) and delete another user's history entry. The active prompt row is not destroyed; the delete impact is against version history. Exploitation requires knowing or obtaining victim history UUIDs, so severity depends on adjacent ID exposure.

Root Cause

The route checks read access only for prompt_id:

# backend/open_webui/routers/prompts.py
prompt = await Prompts.get_prompt_by_id(prompt_id, db=db)
...
if not (
    user.role == 'admin'
    or prompt.user_id == user.id
    or await AccessGrants.has_access(
        user_id=user.id,
        resource_type='prompt',
        resource_id=prompt.id,
        permission='read',
        db=db,
    )
):
    raise HTTPException(...)

But the authorized prompt ID is not passed into the diff sink:

# backend/open_webui/routers/prompts.py
diff = await PromptHistories.compute_diff(from_id, to_id, db=db)

compute_diff() fetches both history entries globally by ID and returns their full snapshots:

# backend/open_webui/models/prompt_history.py
result_from = await db.execute(select(PromptHistory).filter(PromptHistory.id == from_id))
from_entry = result_from.scalars().first()
result_to = await db.execute(select(PromptHistory).filter(PromptHistory.id == to_id))
to_entry = result_to.scalars().first()
...
return {
    'from_snapshot': from_snapshot,
    'to_snapshot': to_snapshot,
    ...
}

There is no check that from_entry.prompt_id == prompt_id or to_entry.prompt_id == prompt_id.

The same missing binding affects two further endpoints. POST .../update/version restores a snapshot fetched globally by version_id:

# backend/open_webui/models/prompts.py — update_prompt_version
history_entry = await PromptHistories.get_history_entry_by_id(version_id, db=session)
...
prompt.content = snapshot.get('content', prompt.content)   # foreign snapshot copied into caller's prompt
prompt.version_id = version_id

DELETE .../history/{history_id} deletes an entry fetched globally by history_id:

# backend/open_webui/models/prompt_history.py — delete_history_entry
result = await db.execute(select(PromptHistory).filter_by(id=history_id))
entry = result.scalars().first()
...
await db.delete(entry)

Neither checks entry.prompt_id == prompt.id. The single-entry read endpoint (GET .../history/{history_id}) does (history_entry.prompt_id != prompt.id → 404); these three endpoints were missing it.

PoC

#!/usr/bin/env python3
"""
PoC for prompt history diff IDOR.

The PoC executes:
  - the real routers.prompts.get_prompt_diff() route function
  - the real PromptHistories.compute_diff() implementation

Fake model/DB adapters are used only to avoid requiring a running server. The…