CVE-2011-0935 in IOS
Summary
by MITRE
The PKI functionality in Cisco IOS 15.0 and 15.1 does not prevent permanent caching of certain public keys, which allows remote attackers to bypass authentication and have unspecified other impact by leveraging an IKE peer relationship in which a key was previously valid but later revoked, aka Bug ID CSCth82164, a different vulnerability than CVE-2010-4685.
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Analysis
by VulDB Data Team • 11/02/2021
The vulnerability described in CVE-2011-0935 represents a critical flaw in Cisco IOS PKI implementation that undermines the security of internet key exchange operations. This issue affects Cisco IOS versions 15.0 and 15.1, where the public key caching mechanism fails to properly invalidate previously cached keys even after they have been revoked. The flaw specifically manifests within IKE peer relationships where a key was initially valid but subsequently revoked from the certificate authority, creating a persistent security risk that can be exploited by remote attackers.
The technical root cause of this vulnerability lies in the improper handling of public key caching within the PKI subsystem of Cisco IOS. When an IKE peer establishes a secure connection, the system caches public keys to improve performance and reduce computational overhead. However, the implementation fails to properly track key revocation status, allowing cached keys to remain active even after they have been invalidated through certificate revocation lists or certificate status protocols. This caching behavior violates fundamental PKI security principles where revoked certificates should not be accepted for authentication purposes. The vulnerability operates at the protocol level within the IKE phase 1 and phase 2 exchanges, specifically impacting the authentication mechanisms that rely on digital signatures and public key cryptography.
The operational impact of this vulnerability extends beyond simple authentication bypass to potentially enable broader security compromises within network infrastructure. Remote attackers can exploit this weakness to establish unauthorized secure connections using previously valid but now revoked certificates, effectively circumventing the intended certificate validation process. This creates opportunities for man-in-the-middle attacks, unauthorized access to network resources, and potential data exfiltration from systems relying on IKE-based VPN connections. The unspecified other impacts suggest that this vulnerability could enable additional attack vectors or compromise other security controls within the affected network infrastructure, making it particularly dangerous in enterprise environments where network security is paramount.
Organizations affected by this vulnerability should implement immediate mitigations including disabling or carefully restricting IKE peer relationships that rely on cached public keys, implementing more frequent certificate validation checks, and ensuring proper certificate revocation distribution mechanisms are in place. The vulnerability aligns with CWE-295 which addresses improper certificate validation, and can be mapped to ATT&CK technique T1552.001 for unsecured credentials and T1071.004 for application layer protocol. Cisco recommends updating to affected IOS versions that contain patches addressing the key caching behavior, implementing additional monitoring for unauthorized certificate usage, and reviewing existing IKE configurations to minimize exposure. Network administrators should also consider implementing certificate status checking mechanisms such as OCSP stapling or CRL distribution points to ensure timely revocation information is available to prevent exploitation of this persistent caching vulnerability.