jackson-inject-security SKILL.md skillA
jackson-inject-security from cxcscmu/skilllearnbench is an agent skill: a SKILL.md folder an AI agent loads when a task calls for it.
mdr add cxcscmu/skilllearnbench/jackson-inject-security@git:20260424.d50cf5aPins git:20260424.d50cf5a in mdr.lock. Pin the fingerprint instead.
- Audit grade
- A, 17 of 17 checks passed
- Kind
- SKILL.md skill
- Repository
- cxcscmu/skilllearnbench
- Path
skills/b1-one-shot-claude-opus-4-6/fix-security-bug/jackson-inject-security/SKILL.md- Versions recorded
- 1
- Latest version
- git:20260424.d50cf5a, committed Apr 24, 2026
- Size
- 1,742 bytes
- Repository stars
- 91
- License
- MIT
Preventing Jackson @JacksonInject override attacks where JSON input can replace server-side injected values.
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
# Jackson @JacksonInject Security
## The Vulnerability
When using `@JacksonInject` in Jackson `@JsonCreator` constructors, JSON input can override server-side injected values by default. This happens because `@JacksonInject` defaults to `useInput = OptBoolean.DEFAULT`, which allows JSON properties to take precedence over injected values.
## Attack Mechanism
If a class has:
```java
@JsonCreator
public MyClass(@JacksonInject MyConfig config) { ... }
```
An attacker can send JSON with `"": {"enabled": true}` to override the injected `config` value. The empty string key `""` maps to inject parameters that have no explicit ID.
Combined with `FAIL_ON_UNKNOWN_PROPERTIES = false` (common in many frameworks), the attack payload passes silently.
## Fix: useInput = OptBoolean.FALSE
Jackson 2.9+ introduced `OptBoolean` for `@JacksonInject`:
```java
import com.fasterxml.jackson.annotation.OptBoolean;
@JsonCreator
public MyClass(
@JacksonInject(useInput = OptBoolean.FALSE) MyConfig config
) { ... }
```
This prevents JSON input from overriding the injected value entirely.
## Additional Defense: Constructor Validation
…Read the whole file at its exact version.
How to install
mdr add cxcscmu/skilllearnbench/jackson-inject-security@sha256:e60f574ccbe14ddfThe line at the top of this page pins the label git:20260424.d50cf5a, 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_twowbtih3lt7sjss)
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Versions
The registry has recorded 1 version of this file, committed on Apr 24, 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 (1742 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
cxcscmu/skilllearnbench · 91 stars · license MIT · pushed 2026-10-02 · branch main
API
GET https://markdownregistry.com/api/v1/artifacts/art_twowbtih3lt7sjss GET https://markdownregistry.com/api/v1/resolve?ref=cxcscmu/skilllearnbench/jackson-inject-security GET https://markdownregistry.com/api/v1/blob/e60f574ccbe14ddf0da4f9878abd29173a9cc9d737db31186946f66ce90a8735
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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.