---
language:
- en
license: apache-2.0
library_name: transformers
tags:
- cybersecurity
- APT
- threat-intelligence
- contrastive-learning
- embeddings
- attribution
- MITRE-ATTACK
- CTI
- ModernBERT
datasets:
- mitre-attack
base_model: cisco-ai/SecureBERT2.0-base
pipeline_tag: feature-extraction
model-index:
- name: FALCON
  results:
  - task:
      type: text-classification
      name: APT Group Attribution
    metrics:
    - type: accuracy
      value: 0.0
      name: Accuracy (5-fold CV)
    - type: f1
      value: 0.0
      name: F1 Weighted (5-fold CV)
    - type: f1
      value: 0.0
      name: F1 Macro (5-fold CV)
---

# FALCON — Finetuned Actor Linking via CONtrastive Learning

<p align="center">
  <strong>A domain-adapted embedding model for automated APT group attribution from cyber threat intelligence text.</strong>
</p>

| | |
|---|---|
| **Developed by** | AIT — Austrian Institute of Technology, Cybersecurity Group |
| **Model type** | Transformer encoder (ModernBERT) with contrastive fine-tuning |
| **Language** | English |
| **License** | Apache 2.0 |
| **Base model** | [cisco-ai/SecureBERT2.0-base](https://huggingface.co/cisco-ai/SecureBERT2.0-base) |
| **Paper** | *Coming soon* |

---

## Model Description

FALCON (**F**inetuned **A**ctor **L**inking via **CON**trastive learning) is a cybersecurity embedding model that maps textual descriptions of attack behaviors to a vector space where descriptions belonging to the same APT group are close together and descriptions from different groups are far apart.

Given a sentence like *"The group has used spearphishing emails with malicious macro-enabled attachments to deliver initial payloads"*, FALCON produces a 768-dimensional embedding that can be used to classify which APT group performed that behavior.

### Training Pipeline

```
cisco-ai/SecureBERT2.0-base (ModernBERT, 150M params)
        ↓
   Tokenizer Extension — Added APT group names + aliases as single tokens
        ↓
   MLM Fine-Tuning — Taught the model meaningful representations for new tokens
        ↓
   Supervised Contrastive Fine-Tuning (SupCon) — Shaped the embedding space
        so same-group descriptions cluster together
        ↓
   FALCON
```

### What Makes FALCON Different

- **Domain-adapted base**: Built on SecureBERT 2.0, which already understands cybersecurity terminology, rather than a generic language model.
- **Contrastive objective**: Unlike classification-only models, FALCON optimizes the embedding geometry directly using Supervised Contrastive Loss (Khosla et al., 2020), producing embeddings suitable for retrieval, clustering, and few-shot classification.
- **Name-agnostic**: Group names are masked during contrastive training with `[MASK]`, forcing the model to learn behavioral patterns rather than memorizing name co-occurrences.
- **Alias-aware tokenizer**: APT group names and their vendor-specific aliases (e.g., APT29, Cozy Bear, Midnight Blizzard, NOBELIUM) are single tokens, preventing subword fragmentation.

---

## Intended Uses

### Direct Use

- **APT group attribution**: Given a behavioral description from a CTI report, classify which threat actor is most likely responsible.
- **Semantic search over CTI**: Retrieve the most relevant threat actor profiles given a description of observed attack behavior.
- **Threat actor clustering**: Group unlabeled incident descriptions by behavioral similarity.
- **Few-shot attribution**: Attribute newly emerging APT groups with very few reference samples.

### Downstream Use

- Fine-tuning for organization-specific threat actor taxonomies.
- Integration into SIEM/SOAR pipelines for automated triage.
- Enrichment of threat intelligence platforms with behavioral similarity scoring.

### Out-of-Scope Use

- Attribution based on IOCs (hashes, IPs, domains) — FALCON operates on natural language text only.
- Real-time network traffic classification.
- Definitive legal or geopolitical attribution — FALCON is a decision-support tool, not an oracle.

---

## How to Use

### Feature Extraction (Embeddings)

```python
import torch
from transformers import AutoModel, AutoTokenizer

model = AutoModel.from_pretrained("ait-cybersec/FALCON")
tokenizer = AutoTokenizer.from_pretrained("ait-cybersec/FALCON")

text = "The group used PowerShell scripts to download and execute additional payloads."

inputs = tokenizer(text, return_tensors="pt", truncation=True, max_length=128)
with torch.no_grad():
    outputs = model(**inputs)

# Mean pooling (recommended)
attention_mask = inputs["attention_mask"].unsqueeze(-1)
token_embs = outputs.last_hidden_state
embedding = (token_embs * attention_mask).sum(dim=1) / attention_mask.sum(dim=1)

print(f"Embedding shape: {embedding.shape}")  # [1, 768]
```

### APT Group Classification (with sklearn probe)

```python
import numpy as np
from sklearn.linear_model import LogisticRegression

# Encode your labeled corpus
train_embeddings = np.array([get_embedding(text) for text in train_texts])
test_embeddings = np.array([get_embedding(text) for text in test_texts])

clf = LogisticRegression(max_iter=2000)
clf.fit(train_embeddings, train_labels)

predictions = clf.predict(test_embeddings)
```

### Semantic Similarity Between Descriptions

```python
from sklearn.metrics.pairwise import cosine_similarity

emb1 = get_embedding("The actor used spearphishing with malicious attachments.")
emb2 = get_embedding("The group sent phishing emails containing weaponized documents.")
emb3 = get_embedding("The adversary exploited a SQL injection vulnerability.")

print(f"Phishing vs Phishing: {cosine_similarity(emb1, emb2)[0][0]:.4f}")  # High
print(f"Phishing vs SQLi:     {cosine_similarity(emb1, emb3)[0][0]:.4f}")  # Lower
```

---

## Training Details

### Training Data

- **Source**: [MITRE ATT&CK Enterprise Groups](https://attack.mitre.org/groups/) — technique usage descriptions for all tracked APT groups.
- **Preprocessing**:
  - Canonicalized group aliases using `GroupID` (e.g., APT29 = Cozy Bear = Midnight Blizzard → single label).
  - Filtered to groups with ≥30 unique technique usage descriptions.
  - Masked all group names and aliases in training text with `[MASK]` to prevent name leakage.
- **Final dataset**: ~144 unique APT groups, variable samples per group (30–200+).

### Training Procedure

#### Stage 1: Tokenizer Extension

Extended the SecureBERT 2.0 tokenizer with APT group names and vendor-specific aliases as single tokens. This prevents names like "Kimsuky" from being split into subword fragments (`['Kim', '##su', '##ky']` → `['Kimsuky']`).

#### Stage 2: Masked Language Modeling (MLM)

| Hyperparameter | Value |
|---|---|
| Base model | cisco-ai/SecureBERT2.0-base |
| Objective | MLM (15% masking probability) |
| Learning rate | 2e-5 |
| Batch size | 16 |
| Epochs | 10 |
| Weight decay | 0.01 |
| Warmup ratio | 0.1 |
| Max sequence length | 128 |
| Text used | Unmasked (model sees group names to learn their embeddings) |

#### Stage 3: Supervised Contrastive Learning (SupCon)

| Hyperparameter | Value |
|---|---|
| Base checkpoint | Stage 2 MLM output |
| Loss function | Supervised Contrastive Loss (Khosla et al., 2020) |
| Temperature | 0.07 |
| Projection head | 768 → 768 (ReLU) → 256 |
| Unfrozen layers | Last 4 transformer layers + projection head |
| Learning rate | 2e-5 |
| Batch size | 64 |
| Epochs | 15 |
| Scheduler | Cosine annealing |
| Gradient clipping | max_norm=1.0 |
| Text used | Masked (group names replaced with `[MASK]`) |

---

## Evaluation

Evaluation uses a **linear probing protocol**: freeze the model, extract embeddings, train a LogisticRegression classifier on top, and report metrics using **5-fold stratified cross-validation** with oversampling applied only to the training fold (no data leakage).

### Results

<!-- UPDATE THESE WITH YOUR ACTUAL RESULTS -->

| Model | Accuracy | F1 Weighted | F1 Macro |
|---|---|---|---|
| SecureBERT 2.0 (frozen baseline, CLS) | — | — | — |
| SecureBERT 2.0 (frozen baseline, Mean) | — | — | — |
| FALCON-base (MLM only) | — | — | — |
| **FALCON (MLM + Contrastive)** | **—** | **—** | **—** |

*Fill in after training completes.*

### Evaluation Protocol Details

- **No data leakage**: Oversampling is applied inside each training fold only; test folds contain only original, unique samples.
- **Name masking**: All group names and aliases are replaced with `[MASK]` in evaluation text, ensuring the model is evaluated on behavioral understanding, not name recognition.
- **Canonicalization**: All vendor-specific aliases are resolved to a single canonical label per `GroupID`, preventing inflated metrics from alias splits.

---

## Comparison with Related Models

| Model | Domain | Architecture | Training Objective | Cybersecurity-Specific |
|---|---|---|---|---|
| BERT base | General | BERT | MLM + NSP | ❌ |
| SecBERT | Cybersecurity | BERT | MLM | ✅ |
| SecureBERT | Cybersecurity | RoBERTa | MLM (custom tokenizer) | ✅ |
| ATTACK-BERT | Cybersecurity | Sentence-BERT | Sentence similarity | ✅ |
| SecureBERT 2.0 | Cybersecurity | ModernBERT | MLM (text + code) | ✅ |
| **FALCON** | **APT Attribution** | **ModernBERT** | **MLM + SupCon** | **✅ (task-specific)** |

---

## Limitations and Bias

- **Training data bias**: MITRE ATT&CK over-represents well-documented state-sponsored groups (APT28, APT29, Lazarus). Less-known actors may have weaker representations.
- **Behavioral overlap**: Many APT groups share identical TTPs (e.g., spearphishing, PowerShell usage). The model cannot reliably distinguish groups that employ the same techniques in the same way.
- **English only**: The model is trained on English-language CTI text and will not perform well on non-English threat reports.
- **Static knowledge**: The model reflects the MITRE ATT&CK knowledge base at training time and does not update as new groups or techniques emerge.
- **Not a replacement for analyst judgment**: FALCON is a decision-support tool. Attribution conclusions should always be validated by human analysts.

---

## Ethical Considerations

Automated threat attribution is a sensitive capability with potential for misuse. Incorrect attribution could lead to misguided defensive actions or geopolitical consequences. Users should:

- Always treat model outputs as **hypotheses**, not conclusions.
- Combine FALCON outputs with additional intelligence sources (IOCs, infrastructure analysis, geopolitical context).
- Be aware that threat actors deliberately employ false-flag operations to mislead attribution.

---

## Citation

```bibtex
@misc{falcon2025,
  title={FALCON: Finetuned Actor Linking via Contrastive Learning for APT Group Attribution},
  author={AIT Austrian Institute of Technology, Cybersecurity Group},
  year={2025},
  url={https://huggingface.co/ait-cybersec/FALCON}
}
```

### Related Work

- Aghaei, E. et al. "SecureBERT 2.0: Advanced Language Model for Cybersecurity Intelligence." arXiv:2510.00240 (2025).
- Khosla, P. et al. "Supervised Contrastive Learning." NeurIPS (2020).
- Irfan, S. et al. "A Comprehensive Survey of APT Attribution." arXiv:2409.11415 (2024).
- Abdeen, B. et al. "SMET: Semantic Mapping of CVE to ATT&CK." (2023).

---

## Model Card Authors

AIT — Austrian Institute of Technology, Cybersecurity Group

## Model Card Contact

For inquiries, please open an issue on this repository or contact the AIT Cybersecurity Group.