A security-testing guide for finding XML external entity (XXE) flaws, where an XML parser is tricked into reading files or contacting internal services.

Use it to test XML endpoints and server-side processing of SVG, office documents, PDFs, SAML messages, feeds, and SOAP services.

It helps expose unsafe XML processing in APIs, uploads, document converters, and sign-in systems.

hunt-xxe — Skill for Claude Code and Codex by adriannoes

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

Any agent

npx skills add adriannoes/awesome-agentic-ai --skill hunt-xxe

Clone the repo

git clone --depth 1 https://github.com/adriannoes/awesome-agentic-ai

Made for: Claude Code, Codex.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

README.md

[![agentmods](https://agentmods.dev/badge/skills/adriannoes/awesome-agentic-ai/hunt-xxe/github.svg)](https://agentmods.dev/skills/adriannoes/awesome-agentic-ai/hunt-xxe)

Your own site

<a href="https://agentmods.dev/skills/adriannoes/awesome-agentic-ai/hunt-xxe"><img src="https://agentmods.dev/badge/skills/adriannoes/awesome-agentic-ai/hunt-xxe/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

Your own site · 80×15

<a href="https://agentmods.dev/skills/adriannoes/awesome-agentic-ai/hunt-xxe"><img src="https://agentmods.dev/badge/skills/adriannoes/awesome-agentic-ai/hunt-xxe.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 31 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.

When invoked 4,623 The whole file, excluding the scripts and references it only reads on demand.

Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe. ✓ AI security review Sonnet 5 · 7 Sept 2026 📄 Read the review

Origin original No closer match found in the catalogue.

Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

Model	Per session	Once invoked
Fable 5.1	$0.00031	$0.04623
Opus 5.5	$0.00012	$0.01849
Sonnet 5.5	$0.00006	$0.00925
Haiku 4.5	$0.00003	$0.00462

Measured 2mo ago against content hash 53455e42e91d, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

hunt-xxe scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2mo ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

cursor-claude-codex/skills/bug-hunter/skills/hunt-xxe/SKILL.md · 367 lines

How it starts

The opening of the file, as written. The whole thing — 367 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Crown Jewel Targets

XXE is a critical-severity vulnerability that consistently pays at the top of bug bounty scales ($5,000–$30,000+) due to its direct path to sensitive data exfiltration and SSRF. Highest-value targets:

Large enterprise platforms with XML-heavy backend integrations (finance, logistics, ride-sharing APIs)
Domains with file-read capability — /etc/passwd, /etc/shadow, internal config files, AWS metadata endpoints
Subdomains sharing backend infrastructure — one XXE endpoint can pivot to internal services across dozens of domains (as demonstrated by 26+ Uber domains via a single entry point)
API gateways accepting XML content types — especially REST APIs that silently accept Content-Type: application/xml
File upload features — SVG, DOCX, XLSX, PDF, PPTX parsers on the server side
SAML/SSO endpoints — SAML assertions are XML-based and frequently vulnerable
Office/document processing services — any feature that converts or processes user-supplied documents

Attack Surface Signals

URL Patterns

/api/v*/xml
/upload
/import
/parse
/convert
/saml/acs
/sso/saml
/feed
/rss
/sitemap
/webdav
/soap/*
/wsdl
/service.asmx
/xmlrpc
/graphql (multipart with XML)

Request/Response Headers

Content-Type: application/xml
Content-Type: text/xml
Content-Type: application/soap+xml
Content-Type: multipart/form-data  ← check file upload fields
Accept: application/xml
X-Content-Type-Options: (absent — good sign of loose parsing)

JavaScript Patterns (source recon)

// Look for in JS bundles
XMLSerializer
DOMParser
parseFromString
new ActiveXObject("Microsoft.XMLDOM")
$.parseXML(
xml2js
libxmljs
lxml

Tech Stack Signals

Java stacks: Spring, Struts, JAX-WS — default XML parsers (SAX, DOM) are XXE-vulnerable without explicit hardening
PHP: simplexml_load_string(), DOMDocument::loadXML() — vulnerable by default pre-PHP 8
Python: lxml, xml.etree (safe by default), xml.sax (unsafe)
Ruby: Nokogiri older versions, REXML
Node.js: xml2js, libxmljs, fast-xml-parser (older versions)
WSDL/SOAP services: Always test — legacy XML parsing virtually guaranteed
File parsers: Apache POI (Java), python-docx, LibreOffice integrations

Read the full file on GitHub · 367 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

2mo ago First seen · 367 lines · 31 tokens per session scan E 53455e42e91d

Subscribe to this mod's changes

hunt-xxe is a skill published in the GitHub repository adriannoes/awesome-agentic-ai (93 stars, last pushed 9d ago), licensed MIT. It adds 31 tokens to every session and 4,623 once invoked, about $0.0001 per session on Opus 5.5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-09-03.

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hunt-xxe