KRACK & FragAttacks

Two attack families against WPA2 client implementations. Both well-disclosed (KRACK 2017, FragAttacks 2021) and largely patched on modern OSes — but the embedded/IoT long tail keeps them in scope for many engagements.

When These Apply

| Family | Target | Patch Status | |---|---|---| | KRACK | WPA2 supplicants in 4-way handshake / GTK / FT / TDLS | Major OSes patched 2017–2018 | | FragAttacks | Frame fragmentation/aggregation across WPA2/3 | Most stacks patched 2021–2022 |

Probability of success today is high only against:

• Embedded OEM devices (cameras, sensors, point-of-sale)
• Old Android phones (<8 unpatched)
• Industrial / SCADA Wi-Fi clients
• Wi-Fi-enabled toys, smart bulbs, no-name IoT

Modern Win11 / iOS 16+ / Android 13+ / hostapd-2.10 are mitigated.

KRACK — Key Reinstallation

The 4-way handshake's M3 retransmission causes the supplicant to reinstall the same PTK with reset nonce/replay counters. Frames encrypted under the reused keystream become decryptable.

bash
# Vanhoef's official test scripts
git clone https://github.com/vanhoefm/krackattacks-scripts
cd krackattacks-scripts/krackattack
sudo ./krack-test-client.py --interface wlan0
# Tests the supplicant on a connected client

Output identifies which CVE variants the client is vulnerable to.

Practical Outcomes

When successful:

• Decryption of WPA2-encrypted frames between client and AP
• TKIP downgrade enables packet injection
• Recovery of session keys for the duration of the affected key cycle

Not a PSK recovery — you don't get the wireless password from KRACK.

FragAttacks — Frame Splicing

FragAttacks abuse 802.11 fragmentation and aggregation to inject frames that mix encrypted and plaintext fragments, or to splice attacker-controlled fragments into legitimate frames.

bash
git clone https://github.com/vanhoefm/fragattacks
cd fragattacks
sudo ./test-fragattacks.py wlan0 --interface wlan0
# Suite of ~12 tests covering each variant

| CVE | Mechanism | |---|---| | CVE-2020-24588 | A-MSDU spoofing — inject crafted A-MSDU subframes | | CVE-2020-24587 | Mixed-key fragment cache poisoning | | CVE-2020-24586 | Decoupled fragment cache → reuse | | CVE-2020-26139 | Forwarding plaintext frames before authentication | | CVE-2020-26140 | Accepting plaintext frames in protected network |

Practical Outcomes

• Inject malicious frames that the client treats as legitimate (HTTP redirect, DNS poison)
• Read decrypted fragments from cached state
• Cross-protect data exfil via crafted A-MSDU

Targeting Workflow

1. Identify the in-scope client (MAC, OS, vendor)
2. Estimate patch likelihood — if modern OS, likely patched; if embedded, likely vulnerable
3. Run the test suite from a controlled AP setup
4. Report each vulnerable variant separately with the matching CVE

bash
# Rogue AP that drives the test
sudo hostapd-mana /tmp/krack_test_ap.conf

# Force client to associate (deauth from real AP, or social-engineer)
sudo aireplay-ng --deauth 5 -a <real-BSSID> -c <client-MAC> wlan0mon

# Run test once associated
sudo ./krack-test-client.py --interface wlan0

Detection

• WIPS may flag deauth-driven roams to attacker AP
• Test scripts generate distinctive frame patterns; modern WIPS recognizes Vanhoef's tooling
• Successful exploitation is essentially silent at protocol level

Reporting

For each vulnerable CVE:

• Client model + firmware version (be specific)
• Variant tested + result (vulnerable / patched / partial)
• Practical impact in the engagement context (decryption only, or injection viable?)
• Remediation: vendor patch URL, mitigation (WPA3 + PMF blocks most)

Key References

• KRACK: krackattacks.com (Vanhoef)
• FragAttacks: fragattacks.com (Vanhoef)
• Original papers: USENIX Security 2017 (KRACK), USENIX Security 2021 (FragAttacks)
• CISA advisories tracking embedded vendor patches
• Source: https://github.com/SnailSploit/offensive-checklist/blob/main/wireless.md