jackson-deserialization-validation SKILL.md skillA
jackson-deserialization-validation 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-deserialization-validation@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-haiku-4-5/fix-security-bug/jackson-deserialization-validation/SKILL.md- Versions recorded
- 1
- Latest version
- git:20260424.d50cf5a, committed Apr 24, 2026
- Size
- 4,399 bytes
- Repository stars
- 91
- License
- MIT
Securing Jackson JSON deserialization by validating input before processing and preventing unknown properties.
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 Deserialization Validation
## Vulnerability Pattern
When Jackson deserializes JSON with unknown properties, if not handled properly, malicious extra properties can bypass validation logic:
```json
{
"validProperty": "legitimate value",
"": {
"enabled": true,
"other": "malicious"
}
}
```
The empty key `""` can be overlooked by simple property checks.
## Jackson Configuration
### 1. Fail on Unknown Properties
```java
@JsonIgnoreProperties(ignoreUnknown = false)
public class MyFilter {
@JsonProperty
private String function;
// This will throw exception on unknown properties
}
```
### 2. Custom Deserialization
```java
@JsonDeserialize(using = CustomDeserializer.class)
public class MyFilter {
// Custom logic during deserialization
}
```
### 3. @JsonAnySetter for Validation
```java
public class MyFilter {
@JsonProperty
private String function;
@JsonAnySetter
public void handleUnknown(String key, Object value) {
if (key == null || key.isEmpty()) {
throw new IllegalArgumentException("Empty property keys not allowed");
}
// Validate other unknown properties
}
}
```
…Read the whole file at its exact version.
How to install
mdr add cxcscmu/skilllearnbench/jackson-deserialization-validation@sha256:7e876302e850d92aThe 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_bhyjjp6ftkx4cqwa)
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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 (4399 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_bhyjjp6ftkx4cqwa GET https://markdownregistry.com/api/v1/resolve?ref=cxcscmu/skilllearnbench/jackson-deserialization-validation GET https://markdownregistry.com/api/v1/blob/7e876302e850d92a0d93350baba13b22bcb24e98954ed06f143e495830983ee8
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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.