vulnerability / NVI-00012010 / Revision 3
Pydantic AI Web chat UI (`Agent.to_web()`, `clai web`): the local chat endpoint does not validate the `Host` header
GitHub lists this reviewed advisory for pydantic-ai, pydantic-ai, pydantic-ai-slim, pydantic-ai-slim. Published version ranges and source prerequisites are shown below; this is not an inspection of a visitor’s application.
This report has not inspected your inventory, configuration, deployed build, reachability or evidence. A catalog listing and a severity score do not establish exposure or compromise.
01 / Meaning
Why it matters
Published affected context helps an owner decide what evidence to gather. This report has not examined your application.
6.4 medium
GitHub source severity; exploitability and local consequence require separate evidence.
As of · GitHub Advisory Database
0.132%
FIRST EPSS model v2026.06.15; exploitation probability over 30 days, percentile 0.02763. Missing scores are unknown.
As of · FIRST EPSS
02 / Applicability
The affected context
Affected versions, configuration prerequisites and known exclusions are public. Confirm each one against the deployed service.
pydantic-ai
source listed>= 1.34.0, < 1.107.5
### Summary The Pydantic AI development web chat UI (`Agent.to_web()`, `clai web`) does not validate the `Host` header of incoming requests. A website a developer visits can use DNS rebinding to make requests to a chat UI running on that developer's machine appear same-origin to the browser, causing the served agent to run and to execute its tools with the privileges and credentials of the local process. ### Details Once a name the attacker controls resolves to the loopback address, the browser treats the request as same-origin, so neither an `Origin` check nor a CSRF token constrains it — a same-origin page can read the served UI and any token in it. Binding the web UI to localhost — the default — does not prevent this. ### Impact Applications and developers serving an agent through `Agent.to_web()` or `clai web`. The consequences depend on the tools the served agent exposes, and can include data disclosure as well as unwanted tool side effects. Current browser protections reduce but do not remove this exposure: Chromium's Local Network Access gates loopback subresource requests, but does not cover top-level navigations, and Safari does not implement it. ### Mitigation Up
pydantic-ai
source listed>= 2.0.0b1, < 2.30.0
### Summary The Pydantic AI development web chat UI (`Agent.to_web()`, `clai web`) does not validate the `Host` header of incoming requests. A website a developer visits can use DNS rebinding to make requests to a chat UI running on that developer's machine appear same-origin to the browser, causing the served agent to run and to execute its tools with the privileges and credentials of the local process. ### Details Once a name the attacker controls resolves to the loopback address, the browser treats the request as same-origin, so neither an `Origin` check nor a CSRF token constrains it — a same-origin page can read the served UI and any token in it. Binding the web UI to localhost — the default — does not prevent this. ### Impact Applications and developers serving an agent through `Agent.to_web()` or `clai web`. The consequences depend on the tools the served agent exposes, and can include data disclosure as well as unwanted tool side effects. Current browser protections reduce but do not remove this exposure: Chromium's Local Network Access gates loopback subresource requests, but does not cover top-level navigations, and Safari does not implement it. ### Mitigation Up
pydantic-ai-slim
source listed>= 1.34.0, < 1.107.5
### Summary The Pydantic AI development web chat UI (`Agent.to_web()`, `clai web`) does not validate the `Host` header of incoming requests. A website a developer visits can use DNS rebinding to make requests to a chat UI running on that developer's machine appear same-origin to the browser, causing the served agent to run and to execute its tools with the privileges and credentials of the local process. ### Details Once a name the attacker controls resolves to the loopback address, the browser treats the request as same-origin, so neither an `Origin` check nor a CSRF token constrains it — a same-origin page can read the served UI and any token in it. Binding the web UI to localhost — the default — does not prevent this. ### Impact Applications and developers serving an agent through `Agent.to_web()` or `clai web`. The consequences depend on the tools the served agent exposes, and can include data disclosure as well as unwanted tool side effects. Current browser protections reduce but do not remove this exposure: Chromium's Local Network Access gates loopback subresource requests, but does not cover top-level navigations, and Safari does not implement it. ### Mitigation Up
pydantic-ai-slim
source listed>= 2.0.0b1, < 2.30.0
### Summary The Pydantic AI development web chat UI (`Agent.to_web()`, `clai web`) does not validate the `Host` header of incoming requests. A website a developer visits can use DNS rebinding to make requests to a chat UI running on that developer's machine appear same-origin to the browser, causing the served agent to run and to execute its tools with the privileges and credentials of the local process. ### Details Once a name the attacker controls resolves to the loopback address, the browser treats the request as same-origin, so neither an `Origin` check nor a CSRF token constrains it — a same-origin page can read the served UI and any token in it. Binding the web UI to localhost — the default — does not prevent this. ### Impact Applications and developers serving an agent through `Agent.to_web()` or `clai web`. The consequences depend on the tools the served agent exposes, and can include data disclosure as well as unwanted tool side effects. Current browser protections reduce but do not remove this exposure: Chromium's Local Network Access gates loopback subresource requests, but does not cover top-level navigations, and Safari does not implement it. ### Mitigation Up
03 / Response
What to do next
- investigate
Identify the exact component and deployed version, examine the linked publisher’s conditions, and retain evidence of any mitigation.
Confirm current vendor support, compatibility and deployment evidence. This report has not tested a fix in your system. FIRST EPSS
A fixed release is not deployment evidence.
Check current vendor support and compatibility. After making a change, verify the deployed build and relevant runtime conditions. Keep the evidence, owner and time. An updated lockfile alone does not prove what is running.
04 / Limits
What this report cannot establish
- Customer inventory, deployment, reachability and exploitation have not been inspected.
05 / Provenance
Sources you can inspect
Each assertion retains its source. Mirrored records may repeat one underlying publisher; additional links are not independent corroboration.
- GHSA-q2xc-rrxj-58x9 ↗
GitHub Advisory Database · vendor advisory
Observed . GitHub Advisory Database; CC-BY-4.0. Each advisory links its original attribution. Null normalizes fields.
- CVE-2026-107292 ↗
FIRST EPSS · official catalog
Observed . FIRST EPSS; probability of exploitation in the next 30 days, not local compromise. Dataset date/model retained; FIRST services terms apply.
Public revision history
Only published revisions appear here. Routine fetches do not create a material-change event.
- Revision 3 ·
Dated EPSS estimate updated; this is not a new disclosure or proof of exploitation.
- Revision 2 ·
Dated EPSS estimate updated; this is not a new disclosure or proof of exploitation.
- Revision 1 ·
First indexed by Null; source disclosure date is shown separately.