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offensive-krack-fragattacks

DevOps & Security
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KRACK (CVE-2017-13077..082) and FragAttacks (CVE-2020-24586..588 + 26139-26147) — key reinstallation, fragmentation, and aggregation attacks against WPA2 supplicants. Covers Vanhoef's test scripts, viability against modern patched stacks (mostly mitigated post-2021), residual unpatched embedded devices and IoT vendors, and the practical limitations of these attacks in modern engagements. Use when assessing legacy supplicants, embedded clients, or vendors with poor patch cadence.

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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

FamilyTargetPatch Status
KRACKWPA2 supplicants in 4-way handshake / GTK / FT / TDLSMajor OSes patched 2017–2018
FragAttacksFrame fragmentation/aggregation across WPA2/3Most 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.

# 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.

git clone https://github.com/vanhoefm/fragattacks
cd fragattacks
sudo ./test-fragattacks.py wlan0 --interface wlan0
# Suite of ~12 tests covering each variant
CVEMechanism
CVE-2020-24588A-MSDU spoofing — inject crafted A-MSDU subframes
CVE-2020-24587Mixed-key fragment cache poisoning
CVE-2020-24586Decoupled fragment cache → reuse
CVE-2020-26139Forwarding plaintext frames before authentication
CVE-2020-26140Accepting 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
# 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