CVE-2021-30004: W1.fi Hostapd Forging Vulnerability

CVE-2021-30004 Overview

CVE-2021-30004 is a cryptographic vulnerability affecting wpa_supplicant and hostapd version 2.9, two widely-used wireless networking components. The vulnerability stems from improper handling of AlgorithmIdentifier parameters in the TLS implementation, specifically within tls/pkcs1.c and tls/x509v3.c. This flaw enables potential forging attacks that could compromise the integrity of certificate validation processes.

Critical Impact

Attackers may exploit AlgorithmIdentifier parameter mishandling to forge cryptographic signatures, potentially bypassing certificate validation in wireless network authentication.

Affected Products

• w1.fi hostapd 2.9
• w1.fi wpa_supplicant 2.9

Discovery Timeline

• 2021-04-02 - CVE-2021-30004 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2021-30004

Vulnerability Analysis

This vulnerability is classified as an Improper Input Validation issue (CWE-20) that affects the cryptographic signature verification process in wpa_supplicant and hostapd. The flaw exists in how AlgorithmIdentifier parameters are processed during TLS certificate parsing operations.

In X.509 certificates and PKCS#1 signatures, the AlgorithmIdentifier structure specifies the cryptographic algorithm used and may include optional parameters. When these parameters are not properly validated, an attacker can manipulate them to create forged signatures that appear valid to the vulnerable software.

The vulnerability impacts network-accessible services without requiring authentication or user interaction. While it does not directly compromise confidentiality or availability, the integrity impact allows attackers to potentially forge cryptographic signatures, which could be leveraged in man-in-the-middle scenarios on wireless networks.

Root Cause

The root cause lies in insufficient validation of AlgorithmIdentifier parameters within the TLS implementation files tls/pkcs1.c and tls/x509v3.c. The code fails to properly verify that the algorithm parameters match expected values or are correctly formatted, allowing crafted inputs to bypass signature verification checks.

Attack Vector

The attack can be performed remotely over the network. An attacker could exploit this vulnerability by presenting specially crafted certificates or signatures during TLS handshake operations. The mishandled AlgorithmIdentifier parameters allow forged signatures to pass validation, potentially enabling:

1. Certificate forgery attacks against wireless clients using wpa_supplicant
2. Rogue access point authentication bypass on hostapd deployments
3. Man-in-the-middle positioning on enterprise wireless networks

The vulnerability does not require any privileges or user interaction to exploit, making it particularly concerning for exposed wireless infrastructure.

Detection Methods for CVE-2021-30004

Indicators of Compromise

• Anomalous TLS handshake failures or certificate validation warnings in wireless authentication logs
• Unexpected certificate presentations during WPA-Enterprise authentication
• Evidence of certificate manipulation attempts in hostapd or wpa_supplicant debug logs

Detection Strategies

• Monitor wpa_supplicant and hostapd logs for unusual certificate validation behavior
• Implement network monitoring for suspicious 802.1X/EAP authentication patterns
• Deploy intrusion detection rules to identify malformed TLS handshake packets
• Audit installed versions of wpa_supplicant and hostapd across all systems

Monitoring Recommendations

• Enable verbose logging for wpa_supplicant and hostapd to capture certificate processing events
• Configure alerts for failed authentication attempts that may indicate exploitation attempts
• Monitor for unexpected changes in wireless client behavior or authentication patterns

How to Mitigate CVE-2021-30004

Immediate Actions Required

• Upgrade wpa_supplicant and hostapd to versions newer than 2.9 that contain the security fix
• Review wireless network configurations for exposure to untrusted networks
• Implement certificate pinning where possible to reduce forgery attack surface
• Consider network segmentation to limit exposure of vulnerable wireless infrastructure

Patch Information

The vulnerability has been addressed in the hostapd/wpa_supplicant codebase. The fix is available in commit a0541334a6394f8237a4393b7372693cd7e96f15, which corrects the AlgorithmIdentifier parameter validation in the affected TLS files. Administrators should apply updates from their distribution's package repositories or compile from source with this fix included. For Gentoo Linux users, security advisory GLSA 202309-16 provides patched packages.

Workarounds

• If patching is not immediately possible, consider using alternative supplicant implementations with proper AlgorithmIdentifier handling
• Implement additional network-level controls such as certificate validation proxies
• Restrict wireless network access to trusted devices using MAC filtering as a temporary measure (note: this is not a security control, only a mitigation layer)

# Verify installed wpa_supplicant version
wpa_supplicant -v

# Verify installed hostapd version
hostapd -v

# On Debian/Ubuntu, update to patched versions
sudo apt update && sudo apt upgrade wpa_supplicant hostapd

# On RHEL/CentOS, update to patched versions
sudo yum update wpa_supplicant hostapd