# XML external entity injection (XXE)

An XML parser resolves untrusted external entities across an unintended file or network boundary.

**Candidate CWE:** [CWE-611](https://cwe.mitre.org/data/definitions/611.html)

## Test hypothesis

In a local XML fixture, compare a literal marker field with one external entity referencing your controlled HTTP canary. Correlate parser input and receiver log; avoid recursive entities and sensitive files.

## Evidence required

The external entity fetch occurs at the parser, or its controlled marker is returned in parsed output. Record whether the consequence is blind fetch or readable content.

## Rule out false positives

Accepting XML or DOCTYPE, a parser error, or a browser-side request without server entity resolution is insufficient.

## Playbook and command references

- [Uploads, downloads, paths, archives, and XML](https://bug-bounty-field-manual.kmahshooq.chatgpt.site/modules/file-boundaries.html) — Follow a file through acceptance, storage, processing, publication, and retrieval while preserving ownership and path boundaries.
- [Server-side fetching and network trust boundaries](https://bug-bounty-field-manual.kmahshooq.chatgpt.site/modules/ssrf-boundary.html) — Separate an intended fetch from a request that reaches a prohibited destination, forwards authority, or exposes a protected response.

[Find the associated command snippets](https://bug-bounty-field-manual.kmahshooq.chatgpt.site/commands.html?q=Uploads%2C%20downloads%2C%20paths%2C%20archives%2C%20and%20XML)

## Referenced by these target playbooks

[Web & API](https://bug-bounty-field-manual.kmahshooq.chatgpt.site/web-api.html) · [OSS & self-hosted](https://bug-bounty-field-manual.kmahshooq.chatgpt.site/oss.html) · [Desktop & extensions](https://bug-bounty-field-manual.kmahshooq.chatgpt.site/desktop.html) · [Mobile](https://bug-bounty-field-manual.kmahshooq.chatgpt.site/mobile.html) · [AI, agents & MCP](https://bug-bounty-field-manual.kmahshooq.chatgpt.site/ai.html)

## Report checklist

- [ ] Capture the affected version, configuration, identities, and object ownership.
- [ ] Preserve a valid baseline and a negative control.
- [ ] Reproduce the forbidden data access, action, or state change on controlled fixtures.
- [ ] Explain the intended security rule and why the observed behavior violates it.
- [ ] State prerequisites, uncertainty, cleanup, and the smallest demonstrated impact.

## Conditional ATT&CK mapping

No direct ATT&CK mapping selected. Record the weakness and demonstrated impact without forcing an adversary-behavior classification. See the [mapping guide](https://bug-bounty-field-manual.kmahshooq.chatgpt.site/attack.html).

## Primary references

- [PortSwigger XXE](https://portswigger.net/web-security/xxe)

[Back to the complete vulnerability catalog](https://bug-bounty-field-manual.kmahshooq.chatgpt.site/vulnerabilities.html)