CVE-2026-56101 Overview
CVE-2026-56101 is an inverted comparison vulnerability in OpenBSD's IEEE 802.11 wireless stack. The flaw resides in the ieee80211_michael_mic_failure() function within sys/net80211/ieee80211_crypto_tkip.c. An unauthenticated attacker within radio frequency (RF) range can trigger a denial of service by transmitting two malformed Temporal Key Integrity Protocol (TKIP) frames separated by more than 60 seconds. The reversed countermeasure window check deauthenticates all associated TKIP stations and blocks reassociation for up to 90 seconds. The same inversion causes legitimate within-window Message Integrity Code (MIC) failures to be silently discarded, allowing key-recovery attempts to proceed undetected.
Critical Impact
Adjacent-network attackers can force disconnection of TKIP-associated wireless clients and suppress countermeasures against active key-recovery attacks.
Affected Products
- OpenBSD prior to commit 1ee99df in sys/net80211/ieee80211_crypto_tkip.c
- Systems using the OpenBSD IEEE 802.11 stack with TKIP encryption enabled
- Wireless access points and clients built on affected OpenBSD releases
Discovery Timeline
- 2026-09-08 - CVE-2026-56101 published to NVD
- 2026-09-10 - Last updated in NVD database
Technical Details for CVE-2026-56101
Vulnerability Analysis
The defect is an inverted conditional check [CWE-697] in the TKIP MIC failure handler. TKIP defines countermeasures that trigger when two Michael MIC failures occur within a 60-second window. This behavior deauthenticates stations and pauses reassociation to defeat active key-recovery attacks. The affected implementation inverts the timing comparison. Countermeasures activate only when MIC failures are separated by more than 60 seconds, and failures inside the window are silently discarded. Attackers gain a reliable denial-of-service primitive while defensive logic against the underlying TKIP weakness is disabled.
Root Cause
The root cause is a reversed if-condition in ieee80211_michael_mic_failure(). The comparison operator that gates countermeasure activation evaluates the opposite of the intended TKIP specification. The upstream fix appears in commit 1ee99df of the OpenBSD source tree.
Attack Vector
Exploitation requires adjacent network access. An attacker within RF range of a TKIP-enabled OpenBSD wireless network transmits two malformed TKIP frames spaced more than 60 seconds apart. This satisfies the inverted comparison and forces the stack to engage countermeasures. All associated TKIP stations are deauthenticated and blocked from reassociating for up to 90 seconds. No credentials or prior authentication are required.
-/* $OpenBSD: ieee80211_crypto_tkip.c,v 1.33 2021/03/10 10:21:48 jsg Exp $ */
+/* $OpenBSD: ieee80211_crypto_tkip.c,v 1.34 2026/07/15 09:47:51 stsp Exp $ */
/*-
* Copyright (c) 2008 Damien Bergamini <damien.bergamini@free.fr>
Source: OpenBSD commit 1ee99df — patch fixing the inverted condition in ieee80211_michael_mic_failure().
Detection Methods for CVE-2026-56101
Indicators of Compromise
- Repeated mass deauthentication events affecting all TKIP-associated stations on an OpenBSD access point
- Recurring 60 to 90 second reassociation blackouts on affected wireless segments
- Kernel or hostapd log entries recording TKIP MIC failure countermeasures triggered by paired frames spaced more than 60 seconds apart
Detection Strategies
- Correlate ieee80211 subsystem log messages with client disconnect timestamps to identify countermeasure-driven outages
- Deploy wireless intrusion detection sensors to capture malformed TKIP frames and MIC failure sequences within RF range
- Baseline normal MIC failure rates and alert on repeated single-frame MIC failures that fall outside the 60-second window
Monitoring Recommendations
- Ingest wireless access point and OpenBSD kernel logs into a central Security Information and Event Management (SIEM) platform for correlation
- Monitor for anomalous client deauthentication bursts targeting TKIP-only Service Set Identifiers (SSIDs)
- Track reassociation failure metrics and alert when downtime windows approach the 90-second countermeasure duration
How to Mitigate CVE-2026-56101
Immediate Actions Required
- Apply the OpenBSD source update at or beyond commit 1ee99df and rebuild affected kernels
- Migrate wireless networks off TKIP to Counter Mode Cipher Block Chaining Message Authentication Code Protocol (CCMP) or Galois/Counter Mode Protocol (GCMP) where feasible
- Restrict physical and RF proximity to critical wireless deployments to reduce adjacent-network exposure
Patch Information
The fix is committed to the OpenBSD source repository as 1ee99dfcc4ddc87afc6395d5d3094e9d2314fb5a. The patch corrects the inverted comparison in ieee80211_michael_mic_failure() so countermeasures activate when two MIC failures occur within 60 seconds, matching the IEEE 802.11 specification. Refer to the VulnCheck OpenBSD Advisory and Argus Systems Advisory #209 for additional context.
Workarounds
- Disable TKIP on all wireless interfaces and enforce CCMP-only or WPA3 configurations
- Decommission legacy TKIP-only SSIDs and move clients to modern encryption suites
- Implement wireless intrusion prevention to block malformed 802.11 frames from unknown transmitters
# Example: enforce CCMP-only (disable TKIP) in hostapd.conf
wpa=2
wpa_key_mgmt=WPA-PSK
wpa_pairwise=CCMP
rsn_pairwise=CCMP
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.