Cisco SD-WAN Solution Buffer Overflow Vulnerability

Vulnerability

A stack buffer overflow vulnerability exists in the confd_cli binary, which is part of the Cisco SD-WAN Solution software (including vSmart, vManage, vBond controllers and vEdge routers). The binary has the SUID bit set and is used to connect to the confd server. The vulnerability is due to insufficient input validation when processing the SSH_CONNECTION environment variable. Specifically, the second argument of this variable is copied into a stack buffer using sprintf() without any length check, allowing an attacker to overflow the buffer [1]. This affects all versions of the Cisco SD-WAN Solution prior to the fixed releases.

Exploitation

An authenticated local attacker can exploit this vulnerability by setting a long SSH_CONNECTION environment variable and then executing confd_cli. The sprintf() call copies the attacker-controlled string into a fixed-size stack buffer, overwriting adjacent memory including the return address. On Intel x86_64 architectures (controllers), the binary is compiled without NX protection, enabling the attacker to redirect execution to a ROP chain for privilege escalation. On MIPS64 big-endian architectures (vEdges), null bytes in userland addresses prevent direct return address overwrite, making exploitation more difficult [1]. The proof of concept demonstrates the overflow by providing a long string of 'a' characters.

Impact

Successful exploitation allows the attacker to achieve local privilege escalation, gaining root-level access on the affected device. With elevated privileges, the attacker can access sensitive information they are not authorized to see and make unauthorized configuration changes to the system [1][2]. This compromises the confidentiality, integrity, and availability of the SD-WAN solution.

Mitigation

Cisco has released software updates to fix this vulnerability. Customers should upgrade to the latest fixed version as specified in the Cisco Security Advisory [2]. No workarounds are available. The vulnerability is not known to be listed in the CISA Known Exploited Vulnerabilities (KEV) catalog. Users should consult the advisory for specific version information and upgrade instructions.