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Message-ID: <047e2b26-5287-4c32-aac8-224292b1b284@oracle.com> Date: Tue, 9 Jul 2024 13:03:28 -0700 From: Alan Coopersmith <alan.coopersmith@...cle.com> To: oss-security@...ts.openwall.com Subject: CVE-2024-3596: RADIUS/UDP vulnerable to improved MD5 collision attack https://kb.cert.org/vuls/id/456537 discloses the new Blast-RADIUS attack: > Overview > -------- > A vulnerability in the RADIUS protocol allows an attacker allows an > attacker to forge an authentication response in cases where a > Message-Authenticator attribute is not required or enforced. This > vulnerability results from a cryptographically insecure integrity > check when validating authentication responses from a RADIUS server. > > Description > ----------- > RADIUS is a popular lightweight authentication protocol used for > networking devices specified in IETF 2058 as early as 1997 (obsoleted > by RFC 2138 and then RFC 2865. There have been several other IETF > standards (RADIUS/TCP, RADIUS/TLS and RADIUS/DTLS) that cover and > enhance various parts of the specification for the use of RADIUS in > authentication. RADIUS is widely used to authenticate both users and > devices and widely supported by networking devices, from basic network > switches to more complex VPN solutions. Recently, RADIUS has also been > adopted in much of the cloud services that provide tiered, role-based > access-control to resources. As a client-server protocol, RADIUS uses > a Request-Response model to verify authentication requests and further > provide any role-based access using Groups. RADIUS can also be proxied > to support multi-tenant roaming access services. > > A vulnerability in the verification of RADIUS Response from a RADIUS > server has been disclosed by a team of researchers from UC San Diego > and their partners. An attacker, with access to the network where the > RADIUS protocol is being transmitted, can spoof a UDP-based RADIUS > Response packet to modify any valid Response (Access-Accept, > Access-Reject, or Access-Challenge) to any other response, with almost > any content, completely under the attackers control. This allows the > attacker to transform a Reject into an Accept without knowledge of the > shared secret between the RADIUS client and server. The attack is > possible due to a basic flaw in the RADIUS protocol specification that > uses a MD5 hash to verify the response, along with the fact that part > of the hashed text is predictable allowing for a chosen-prefix > collision. The attack, demonstrated by UCSD team, takes advantage of > the chosen-prefix collision of the MD5 message in a novel way. The > widespread use of RADIUS and its adoption into the cloud allows for > such attacks to pose a reasonable threat to the authentication > verification process that relies on RADIUS. > > RADIUS servers that only perform Extensible Authentication Protocol > (EAP), as specified in RFC 3579, are unaffected by this attack. The > EAP authentication messages require the Message-Authenticator > attribute, which will prevent these attacks from succeeding. The use > of TLS (or DTLS) encryption can also prevent such attacks from > succeeding. However, RADIUS over TCP itself can still be susceptible > to this attack, with more advanced man-in-the-middle scenarios, to > successfully attack the TCP connection. > > Finally as explained by Alan Dekok, developer of FreeRadius open > source software - > > The key to the attack is that in many cases, Access-Request > packets have no authentication or integrity checks. An attacker > can then perform a chosen prefix attack, which allows modifying > the Access-Request in order to replace a valid response with one > chosen by the attacker. Even though the response is authenticated > and integrity checked, the chosen prefix vulnerability allows the > attacker to modify the response packet, almost at will. > > Impact > ------ > An attacker with access to the network where RADIUS Access-Request is > transported can craft a response to the RADIUS server irrespective of > the type of response (Access-Accept, Access-Reject, Access-Challenge, > or Protocol-Error) to modify the response to any of the valid > responses. This can allow an attacker to change the Reject response to > an Accept or vice versa. The attack can also potentially intercept an > Access-Challenge, typically used in Multi-Factor Authentication (MFA), > and modify it to an Access-Accept, thus bypassing the MFA used within > RADIUS. Due to the flexible, proxied nature of the RADIUS protocol, > any server in the chain of proxied RADIUS servers can be targeted to > succeed in the attack. > > Solution > -------- > RADIUS-compliant software and hardware manufacturers should adopt the > recommendations from the > https://networkradius.com/assets/pdf/radius_and_md5_collisions.pdf > document to mitigate the risk of the RADIUS protocol limitations > identified in this attack. Manufacturers who bundle the open-source > RADIUS implementations, such as FreeRadius, should update to the > latest available software for both clients and servers and, at a > minimum, require the use of the Message-Authenticator for RADIUS > authentication. > > Network operators who rely on the RADIUS-based protocol for device > and/or user authentication should update their software and > configuration to a secure form of the protocol for both clients and > servers. This can be done by enforcing TLS or DTLS encryption to > secure the communications between the RADIUS client and server. Where > possible, network isolation and secure VPN tunnel communications > should be enforced for the RADIUS protocol to restrict access to these > network resources from untrusted sources. https://blog.cloudflare.com/radius-udp-vulnerable-md5-attack/ provides additional detail, including: > The IETF is an important venue for standardizing network protocols > like RADIUS. The IETF’s radext working group is currently considering > an initiative to deprecate RADIUS/UDP and create a “standards track” > specification of RADIUS over TLS or DTLS, that should help accelerate > the deployment of RADIUS/TLS in the field. We hope that our work will > accelerate the community’s ongoing efforts to secure RADIUS and reduce > its reliance on MD5. https://www.blastradius.fail/ has further details from the researchers. https://www.freeradius.org/security/ provides a lengthy response from the FreeRADIUS maintainers. -- -Alan Coopersmith- alan.coopersmith@...cle.com Oracle Solaris Engineering - https://blogs.oracle.com/solaris
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