Date: Mon, 8 Jun 2020 18:18:01 +0300 From: Jouni Malinen <j@...fi> To: oss-security@...ts.openwall.com Subject: hostapd: UPnP SUBSCRIBE misbehavior in hostapd WPS AP Published: June 8, 2020 Identifiers: - VU#339275 and CVE-2020-12695 (applying for the callback URL in other network case, but not the other items discussed in this advisory) Latest version available from: https://w1.fi/security/2020-1/ Vulnerability General security vulnerability in the way the callback URLs in the UPnP SUBSCRIBE command are used were reported (VU#339275, CVE-2020-12695). Some of the described issues may be applicable to the use of UPnP in WPS AP mode functionality for supporting external registrars. Such issues could allow a device connected to the local network (i.e., a device that has been authorized to transmit packets in the network in which the AP is located) could trigger the AP to initiate a HTTP (TCP/IP) connection to an arbitrary URL, including connections to servers in external networks. This could have a security implication if traffic from the local network to external destinations have different rules (e.g., firewall and packet inspection) for different local hosts and the AP having access to external hosts while the attacker controlled local device not having such access. Such deployment cases may not be common for networks where WPS would be enabled, but it is not possible to completely rule out the applicability to cases where hostapd is used to control a WPS enabled AP. In addition to the more generic issues with the UPnP protocol, couple of implementation specific issues in hostapd were discovered while reviewing this area of the WPS implementation. These issues could allow local devices (i.e., devices that have been authorized to transmit packets in the network in which the AP is located) to trigger misbehavior in hostapd and cause the process to either get terminated or to start using more CPU resources by using a specially constructed SUBSCRIBE command. All these issues require the attacker to be able to discover the UPnP service provided by hostapd and to open a TCP connection toward the IP address of the AP. The former requires access to the local network to be able to receive broadcast packets and the latter requires access to initiate TCP/IP connection to the IP address used by the AP. In most common AP deployment cases, both of these operations are available only from the local network. Vulnerable versions/configurations All hostapd versions with WPS AP support with UPnP enabled in the build parameters (CONFIG_WPS_UPNP=y) and in the runtime configuration (upnp_iface). Possible mitigation steps - Disable WPS UPnP support in the hostapd runtime configuration by removing the upnp_iface parameter. - Merge the following commits to hostapd and rebuild: For CVE-2020-12695: WPS UPnP: Do not allow event subscriptions with URLs to other networks For the other issues: WPS UPnP: Fix event message generation using a long URL path WPS UPnP: Handle HTTP initiation failures for events more properly These patches are available from https://w1.fi/security/2020-1/ - Update to hostapd v2.10 or newer, once available -- Jouni Malinen PGP id EFC895FA
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