high CVSS 7.1

CVE-2026-25640·Python vulnerability

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.

Severity
high
Software
Python
Fixed in
1.51.0
Published
2026-02-06

Affected versions

From: 1.34.0

Until: 1.51.0

Fixed in: 1.51.0

How to fix this CVE

Update Pydantic AI to version 1.51.0 or later to patch the path traversal vulnerability in the web UI component. This vulnerability allows attackers to inject malicious JavaScript through a crafted URL parameter when the chat interface is exposed via Agent.to_web() or the CLI. Immediately apply this update if you are running Pydantic AI versions 1.34.0 through 1.50.x, particularly if your application serves a web-based chat interface.

sudo dnf update python3-pydantic-ai

Defensia detects this vulnerability

What an exploitation attempt looks like

Sample log line indicative of exploitation attempts:

GET requests to web UI endpoint with version parameter containing path traversal sequences (e.g., 'version=../../../malicious') or unusual CDN domain references in the referer or Host header

WAF mitigation (if patching is not yet possible)

Add this rule to your WAF to block exploitation attempts while you schedule the patch. 

Implement URL parameter validation to reject any 'version' query parameters containing path traversal characters (../, .., %2e%2e). Whitelist only numeric version identifiers matching the pattern '^[0-9]+\.[0-9]+\.[0-9]+$' to block exploitation attempts.

How to check if you are affected

  1. Check installed Pydantic AI version: python3 -c "import pydantic_ai; print(pydantic_ai.__version__)"
  2. Verify if Agent.to_web() or CLI chat interface is exposed: grep -r "to_web\|clai web" /path/to/application/code
  3. Review web server logs for suspicious CDN URL requests containing path traversal sequences (../) in the version query parameter
  4. Confirm remediation by re-running the version check and confirming output is 1.51.0 or later

FAQ

What is CVE-2026-25640?

CVE-2026-25640 is a path traversal vulnerability in Pydantic AI's web UI component that enables attackers to serve malicious JavaScript by manipulating the CDN version parameter in URLs. When users click a crafted link or load it in an iframe, the attacker's code executes in their browser, potentially stealing chat history and session data.

Is CVE-2026-25640 being actively exploited?

No, this vulnerability is not currently listed in CISA's Known Exploited Vulnerabilities (KEV) catalog, and there are no publicly available exploits. However, the relatively low complexity of exploitation means proactive patching is strongly recommended.

What versions of Pydantic AI are affected by CVE-2026-25640?

Versions 1.34.0 through 1.50.x are affected. Version 1.51.0 and later contain the fix.

How do I check if my server is vulnerable to CVE-2026-25640?

Run 'python3 -c "import pydantic_ai; print(pydantic_ai.__version__)"' and verify the output is 1.51.0 or later. Also confirm whether Agent.to_web() or 'clai web' are in use in your codebase.

Does Defensia detect CVE-2026-25640?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If Pydantic AI is installed on a monitored server, CVE-2026-25640 will appear in your dashboard with remediation steps.

Related Python CVEs

CVE-2026-34938CVSS 10PraisonAI is a multi-agent teams system. Prior to version 1.5.90, execute_code() in praisonai-agents runs attacker-controlled Python inside a three-layer sandbox that can be fully bypassed by passing a str subclass with an overridden startswith() method to the _safe_getattr wrapper, achieving arbitrary OS command execution on the host. This issue has been patched in version 1.5.90.
CVE-2026-33054CVSS 10Mesop is a Python-based UI framework that allows users to build web applications. Versions 1.2.2 and below contain a Path Traversal vulnerability that allows any user supplying an untrusted state_token through the UI stream payload to arbitrarily target files on the disk under the standard file-based runtime backend. This can result in application denial of service (via crash loops when reading non-msgpack target files as configurations), or arbitrary file manipulation. This vulnerability heavily exposes systems hosted utilizing FileStateSessionBackend. Unauthorized malicious actors could interact with arbitrary payloads overwriting or explicitly removing underlying service resources natively outside the application bounds. This issue has been fixed in version 1.2.3.
CVE-2026-28505CVSS 10Tautulli is a Python based monitoring and tracking tool for Plex Media Server. Prior to version 2.17.0, the str_eval() function in notification_handler.py implements a sandboxed eval() for notification text templates. The sandbox attempts to restrict callable names by inspecting code.co_names of the compiled code object. However, co_names only contains names from the outer code object. When a lambda expression is used, it creates a nested code object whose attribute accesses are stored in code.co_consts, NOT in code.co_names. The sandbox never inspects nested code objects. This issue has been patched in version 2.17.0.
CVE-2026-25632CVSS 10EPyT-Flow is a Python package designed for the easy generation of hydraulic and water quality scenario data of water distribution networks. Prior to 0.16.1, EPyT-Flow’s REST API parses attacker-controlled JSON request bodies using a custom deserializer (my_load_from_json) that supports a type field. When type is present, the deserializer dynamically imports an attacker-specified module/class and instantiates it with attacker-supplied arguments. This allows invoking dangerous classes such as subprocess.Popen, which can lead to OS command execution during JSON parsing. This also affects the loading of JSON files. This vulnerability is fixed in 0.16.1.
CVE-2026-8476CVSS 9.9IBM Langflow OSS 1.0.0 through 1.10.0 contain a critical remote code execution vulnerability in the disk-based caching mechanism. The AsyncDiskCache class uses Python's unsafe pickle.loads() function to deserialize cached objects from disk without validation, integrity verification, or authentication, enabling arbitrary code execution when malicious pickle payloads are processed. Attackers who can influence cached data through file system access, malicious workflow inputs, custom components, or API manipulation can achieve complete system compromise with the privileges of the Langflow server process.

References

Track CVEs across your fleet automatically

Defensia scans your Linux servers and tells you exactly which ones are running vulnerable versions — including CVE-2026-25640. Free for 1 server.

Get started free