Vulnerability · Published Feb 6, 2026 · Assigned by GitHub_M
CVE-2026-25640Pydantic AI affected by Stored XSS via Path Traversal in Web UI CDN URL
High 7.1
In plain English
A high-severity path traversal in pydantic-ai from pydantic. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 31% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
Pydantic AI is a Python agent framework for building applications and workflows with Generative AI. From 1.34.0 to before 1.51.0, a path traversal vulnerability in the Pydantic AI web UI allows an attacker to serve arbitrary JavaScript in the context of the application by crafting a malicious URL. In affected versions, the CDN URL is constructed using a version query parameter from the request URL. This parameter is not validated, allowing path traversal sequences that cause the server to fetch and serve attacker-controlled HTML/JavaScript from an arbitrary source on the same CDN, instead of the legitimate chat UI package. If a victim clicks the link or visits it via an iframe, attacker-controlled code executes in their browser, enabling theft of chat history and other client-side data. This vulnerability only affects applications that use Agent.to_web to serve a chat interface and clai web to serve a chat interface from the CLI. These are typically run locally (on localhost), but may also be deployed on a remote server. This vulnerability is fixed in 1.51.0.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| PyPI | pydantic-ai | 1.51.0 | GHSA-wjp5-868j-wqv7 |
| PyPI | pydantic-ai | 1.51.0 | PYSEC-2026-2979 |
| PyPI | pydantic-ai-slim | 1.51.0 | GHSA-wjp5-868j-wqv7 |
| PyPI | pydantic-ai-slim | 1.51.0 | PYSEC-2026-2983 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| pydantic | pydantic-ai | >= 1.34.0, < 1.51.0 |
Weakness: CWE-22, CWE-79 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:L/A:N
References
- https://github.com/pydantic/pydantic-ai/security/advisories/GHSA-wjp5-868j-wqv7 x_refsource_CONFIRM
- https://github.com/pydantic/pydantic-ai/releases/tag/v1.51.0 x_refsource_MISC
- https://access.redhat.com/security/cve/CVE-2026-25640 vdb-entry, x_refsource_REDHAT
- RHBZ#2437753 issue-tracking, x_refsource_REDHAT
- https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-25640.json x_sadp-csaf-vex