Summary
Open WebUI: Private channel messages can be disclosed through cross-channel thread parent_id binding
A normal authenticated user can read the content of a message in a private channel they do not belong to. GET /api/v1/channels/{id}/messages/{message_id}/thread authorizes the caller against the URL channel, but the underlying thread lookup loads the thread parent by id and returns it without verifying the parent belongs to that channel. By requesting a thread in a channel they can access while supplying a victim channel's message id as the thread root, the attacker receives the victim message, content, channel id, and author.
Affected component
backend/open_webui/models/messages.py,get_messages_by_parent_id()backend/open_webui/routers/channels.py,get_channel_thread_messages()(read),new_message_handler()(parent/reply binding on write)
Root cause
get_messages_by_parent_id(channel_id, parent_id) filters the thread replies by channel_id, but loads the thread parent by id alone and appends it without requiring parent.channel_id == channel_id:
message = await db.get(Message, parent_id) # loaded by id only, no channel binding
if not message:
return []
# replies are filtered by channel_id ...
if len(all_messages) < limit:
all_messages.append(message) # parent appended unconditionally
get_channel_thread_messages() authorizes only the URL channel, then calls get_messages_by_parent_id(id, message_id) with the caller-supplied message_id. The reply insert path (new_message_handler → insert_new_message) also stored a caller-supplied parent_id without binding it to the channel.
Proof of Concept
(reporter) Validated on v0.9.6: GET /channels/{attacker_channel}/messages/{victim_message_id}/thread returned the victim's private message, content, victim channel id, and author, although direct reads of the victim channel returned 403.
Affected / Patched
- Affected:
< 0.10.0(last affected release 0.9.6) - Patched: v0.10.0 (PR #25766).
get_messages_by_parent_idbinds the thread parent to the requested channel (returns[]unlessparent.channel_id == channel_id), andnew_message_handlerrejects a caller-suppliedparent_id/reply_to_idwhose message does not belong to the channel.
Impact
A non-member can disclose the content (plus channel id and author metadata) of a private-channel message whose id they know or obtain. Direct reads of the victim channel/message/thread return 403; the disclosure is via the thread parent of a channel the attacker can access. Read-only, one message per known id.
CVE-2026-59215 has a CVSS score of 3.1 (Low). The vector is network-reachable, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (0.10.0); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Bind the thread parent to the requested channel: get_messages_by_parent_id returns [] unless the parent exists and parent.channel_id == channel_id. Defence-in-depth on the write path: new_message_handler rejects a supplied parent_id/reply_to_id whose message does not belong to the URL channel.
Frequently Asked Questions
- What is CVE-2026-59215? CVE-2026-59215 is a low-severity security vulnerability in open-webui (pip), affecting versions < 0.10.0. It is fixed in 0.10.0.
- How severe is CVE-2026-59215? CVE-2026-59215 has a CVSS score of 3.1 (Low). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of open-webui are affected by CVE-2026-59215? open-webui (pip) versions < 0.10.0 is affected.
- Is there a fix for CVE-2026-59215? Yes. CVE-2026-59215 is fixed in 0.10.0. Upgrade to this version or later.
- Is CVE-2026-59215 exploitable, and should I be worried? Whether CVE-2026-59215 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-59215 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-59215? Upgrade
open-webuito 0.10.0 or later.