parser-differential-bypass SKILL.md skillA
parser-differential-bypass from dreadnode/capabilities is an agent skill: a SKILL.md folder an AI agent loads when a task calls for it.
mdr add dreadnode/capabilities/parser-differential-bypass@git:20260504.2a64374Pins git:20260504.2a64374 in mdr.lock. Pin the fingerprint instead.
- Audit grade
- A, 17 of 17 checks passed
- Kind
- SKILL.md skill
- Repository
- dreadnode/capabilities
- Path
capabilities/web-security/skills/parser-differential-bypass/SKILL.md- Versions recorded
- 1
- Latest version
- git:20260504.2a64374, committed May 4, 2026
- Size
- 4,532 bytes
- Repository stars
- 22
- License
- MIT
Exploit parsing differences between frontend/backend, proxy/origin, or WAF/app to bypass auth, ACLs, and input validation. Use when multiple layers process the same request differently.
Collected from public GitHub. Every version is saved exactly as it was and never changes. Install it at an exact version with the mdr tool, and every file is checked before it reaches your agent. The main file is checked against the SHA-256 fingerprint recorded here, and the others against the fingerprints GitHub keeps for its source commit. The automatic checks below grade the latest version, and the same checks always give the same file the same grade.
What the file says
# Parser Differential Bypass
## Pattern
- Multiple processing layers (proxy, WAF, CDN, app server) parse the same input
- Frontend validates one interpretation, backend acts on another
- Auth or ACL decisions made by a different parser than the one executing the request
## Techniques
### Duplicate JSON Keys
Send the same key twice — parsers disagree on which value wins:
```json
{"role":"user","role":"admin"}
```
- RFC 8259 says duplicate keys have undefined behavior
- First-wins: Python `json.loads()` (older), Go `encoding/json`
- Last-wins: Python `json.loads()` (3.9+), JavaScript `JSON.parse()`, Ruby, PHP
- Test: Submit duplicate keys for any auth/role/permission field. If frontend validates first value but backend uses last (or vice versa), auth bypass.
### Double Authorization Headers
```http
Authorization: Bearer user_token
Authorization: Bearer admin_token
```
- HTTP/1.1 RFC 7230: multiple identical headers should be treated as comma-separated list
- In practice: proxies often validate first, backends often use last
- Nginx: forwards first header. Apache: forwards last. Express: uses first. Spring: uses last.
…Read the whole file at its exact version.
How to install
mdr add dreadnode/capabilities/parser-differential-bypass@sha256:05ef5ba317739bb3The line at the top of this page pins the label git:20260504.2a64374, which is what most people want. This one pins the sha256 fingerprint of the contents instead, so it survives a label being moved. Either way the exact version is written to mdr.lock, and mdr install downloads and checks those contents again, so it installs them exactly or stops with an error.
[](https://markdownregistry.com/a/art_ojq6flj3hajmgdrk)
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Versions
The registry has recorded 1 version of this file, committed on May 4, 2026.
Audit of the latest version
- pass: Frontmatter block present
- pass: Frontmatter declares a name
- pass: Frontmatter declares a description
- pass: Size between 200 bytes and 200 KB (4532 bytes)
- pass: No zero-width or bidi control characters
- pass: No instruction hidden inside an HTML comment
- pass: No link to an exfiltration or paste host
- pass: No credential-shaped string
- pass: No instruction to send local credentials anywhere
- pass: No text hidden with inline styles
- pass: No prompt-injection phrasing
- pass: No curl or wget piped into a shell
- pass: No recursive delete of root, home or parent
- pass: No instruction to read or print local credentials
- pass: No base64 blob over 200 characters
- pass: No link to a raw IP address
- pass: No script tag
Source
dreadnode/capabilities · 22 stars · license MIT · pushed 2026-11-02 · branch main
API
GET https://markdownregistry.com/api/v1/artifacts/art_ojq6flj3hajmgdrk GET https://markdownregistry.com/api/v1/resolve?ref=dreadnode/capabilities/parser-differential-bypass GET https://markdownregistry.com/api/v1/blob/05ef5ba317739bb387ad01150fe03a156ab017fb05f95b48eddf326726b5626a
Your AI assistant does the legwork. You hear about the deals worth your word. Hand yours the standing instructions at modelranch.com and it joins the network that reads files like this one.
Guides: the SKILL.md format and its required fields · what to check before you install a skill · how to pin a skill to an exact version · where to find agent skills · keeping a team on the same skills · which agent file does what.