PYSEC-2026-1532

Summary

A LLM application leveraging XMLToolMessage class may be exposed to untrusted XML input that could result in DoS and/or exposing local files with sensitive information.

Details

XMLToolMessage uses lxml without safeguards: https://github.com/langroid/langroid/blob/df6227e6c079ec22bb2768498423148d6685acff/langroid/agent/xml_tool_message.py#L51-L52 lxml is vulnerable to quadratic blowup attacks and processes external entity declarations for local files by default. Check here: https://pypi.org/project/defusedxml/#python-xml-libraries

PoC

A typical Quadratic blowup XML payload looks like this:

<!DOCTYPE bomb [
<!ENTITY a "aaaaaaaaaa">
<!ENTITY b "&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;">
<!ENTITY c "&b;&b;&b;&b;&b;&b;&b;&b;&b;&b;">
]>
<bomb>&c;</bomb>

Here, &a; expands to 10 characters, &b; expands to 100, and &c; expands to 1000, causing exponential memory usage and potentially crashing the application.

Fix

Langroid 0.53.4 initializes XMLParser with flags to prevent XML External Entity (XXE), billion laughs, and external DTD attacks by disabling entity resolution, DTD loading, and network access. https://github.com/langroid/langroid/commit/36e7e7db4dd1636de225c2c66c84052b1e9ac3c3