Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx skills add cxcscmu/SkillLearnBench --skill jackson-injection-securitygit clone --depth 1 https://github.com/cxcscmu/SkillLearnBenchWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/skills/cxcscmu/skilllearnbench/jackson-injection-security)<a href="https://agentmods.dev/skills/cxcscmu/skilllearnbench/jackson-injection-security"><img src="https://agentmods.dev/badge/skills/cxcscmu/skilllearnbench/jackson-injection-security.svg" alt="Measured on agentmods" height="20"></a>What it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00030 | $0.00620 |
| Opus 5 | $0.00015 | $0.00310 |
| Sonnet 5 | $0.00006 | $0.00124 |
| Haiku 4.5 | $0.00003 | $0.00062 |
Grade A, and why
jackson-injection-security scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 3d ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
How it starts
The opening of the file, as written. The whole thing — 81 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Jackson @JacksonInject Security
The Vulnerability Pattern
When a @JsonCreator constructor uses @JacksonInject without useInput = OptBoolean.FALSE,
Jackson can fall back to JSON input to provide the injectable value. This is exploitable when:
- The injectable ID (default: empty string
"") matches a JSON property key - The JSON property contains a deserializable value of the expected type
- This overrides the server-configured injected value (e.g., security settings)
Example Vulnerable Code
@JsonCreator
public SomeFilter(
@JsonProperty("dimension") String dimension,
@JacksonInject SecurityConfig config // VULNERABLE: can be overridden via JSON ""
)
Exploit Pattern
{
"dimension": "value",
"": {"securityEnabled": false} // Empty key "" overrides @JacksonInject default id
}
The Fix
Option 1: useInput = OptBoolean.FALSE (Recommended for Jackson 2.9+)
import com.fasterxml.jackson.annotation.OptBoolean;
@JsonCreator
public SomeFilter(
@JsonProperty("dimension") String dimension,
@JacksonInject(useInput = OptBoolean.FALSE) SecurityConfig config // FIXED
)
This tells Jackson: NEVER use JSON to provide this value, ALWAYS use InjectableValues only.
Option 2: Explicit Injectable ID (prevents empty string match)
@JacksonInject("securityConfig") // Named ID that won't match "" key
SecurityConfig config
Option 3: Server-side validation before processing
// Validate BEFORE Jackson deserialization or AFTER using Guice-injected config
@Inject
public MyService(SecurityConfig trustedConfig) {
this.trustedConfig = trustedConfig; // From Guice, not from Jackson
}
@JacksonInject Behavior Summary
useInput value |
Behavior |
|---|---|
OptBoolean.DEFAULT |
Use InjectableValues if present; may fall back to JSON |
OptBoolean.TRUE |
JSON input takes precedence over InjectableValues |
OptBoolean.FALSE |
ONLY use InjectableValues; NEVER read from JSON |
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 3d ago First seen · 81 lines · 30 tokens per session scan A d0aa5784618b
jackson-injection-security is a skill published in the GitHub repository cxcscmu/SkillLearnBench (83 stars, last pushed 1mo ago), licensed MIT. It adds 30 tokens to every session and 620 once invoked, about $0.0002 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-09-03.
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