Ssh-2.0-cisco-1.25 Vulnerability -
Internal flaws inside the Cisco-1.25 software state machine expose core enterprise routing switches to memory corruption and unexpected crashes.
SSH-2.0-Cisco-1.25 is a specific version of the SSH protocol implementation developed by Cisco. It is used to establish secure connections between a client and a server, allowing administrators to remotely access and manage network devices. The "2.0" in the version string refers to the SSH protocol version 2, which is a widely used and considered secure version of the protocol.
While often overlooked, this banner carries critical information about the device's software base and can be associated with specific security quirks, compatibility issues, and potential reconnaissance risks. This article provides a comprehensive analysis of the SSH-2.0-Cisco-1.25 banner, the nature of the underlying SSH server, its associated vulnerabilities, and the security implications for enterprise networks.
Why that banner matters
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The string SSH-2.0-Cisco-1.25 is a key part of the initial handshake defined in the SSH protocol specification. When a client connects to an SSH server, the server immediately sends a human-readable identification string identifying the software version. In this specific string, SSH-2.0 indicates the protocol version, Cisco identifies the vendor, and 1.25 is a vendor-specific version string that can vary based on the device platform and software release.
The SSH banner string SSH-2.0-Cisco-1.25 indicates that the target device is running Cisco's legacy SSH implementation, typically found on older Cisco IOS, IOS-XE, or PIX/ASA software versions. This specific version string is widely associated with Cisco devices operating on older, potentially unsupported software trains. ssh-2.0-cisco-1.25 vulnerability
In 2025, Cisco announced CVE-2025-20159, a critical vulnerability affecting the management interface ACL processing in Cisco IOS XR Software. This vulnerability allows an unauthenticated, remote attacker to completely bypass configured access control lists (ACLs) for SSH, NetConf, and gRPC features. This is a severe failure because management ACLs are intended to be the last line of defense, restricting which IP addresses can reach the device's management plane. A bypass renders these access rules completely ineffective.
If immediate patching is not possible, consider temporarily disabling RSA-based public key authentication if it is the primary vector for a known bypass. CVE-2020-3200 Detail - NVD
The most famous vulnerability associated with this version string is the Cisco "Small SSH" issue. Early implementations of SSH on Cisco IOS had a flaw in the key exchange mechanism. In certain configurations, an attacker could bypass authentication entirely. If a device reports this version string, it is highly likely susceptible to authentication bypass, allowing an attacker to gain administrative access without a password. Internal flaws inside the Cisco-1
The SSH-2.0-Cisco-1.25 vulnerability is a serious security issue that requires immediate attention. By understanding the vulnerability and taking steps to mitigate it, organizations can protect their Cisco devices and prevent potential security breaches.
Moral: Treat unexpected SSH banners as a signal to investigate, not ignore. With containment, identification, mitigations, timely patching, and improved processes, small teams can keep critical infrastructure safe.
Devices exposing this banner generally span several generations of Cisco software, making them vulnerable to several critical flaws depending on the exact implementation. The "2
Internal flaws inside the Cisco-1.25 software state machine expose core enterprise routing switches to memory corruption and unexpected crashes.
SSH-2.0-Cisco-1.25 is a specific version of the SSH protocol implementation developed by Cisco. It is used to establish secure connections between a client and a server, allowing administrators to remotely access and manage network devices. The "2.0" in the version string refers to the SSH protocol version 2, which is a widely used and considered secure version of the protocol.
While often overlooked, this banner carries critical information about the device's software base and can be associated with specific security quirks, compatibility issues, and potential reconnaissance risks. This article provides a comprehensive analysis of the SSH-2.0-Cisco-1.25 banner, the nature of the underlying SSH server, its associated vulnerabilities, and the security implications for enterprise networks.
Why that banner matters
This public link is valid for 7 days and shares a thread, including any personal information you added. This link or copies made by others cannot be deleted. If you share with third parties, their policies apply. Can’t copy the link right now. Try again later.
The string SSH-2.0-Cisco-1.25 is a key part of the initial handshake defined in the SSH protocol specification. When a client connects to an SSH server, the server immediately sends a human-readable identification string identifying the software version. In this specific string, SSH-2.0 indicates the protocol version, Cisco identifies the vendor, and 1.25 is a vendor-specific version string that can vary based on the device platform and software release.
The SSH banner string SSH-2.0-Cisco-1.25 indicates that the target device is running Cisco's legacy SSH implementation, typically found on older Cisco IOS, IOS-XE, or PIX/ASA software versions. This specific version string is widely associated with Cisco devices operating on older, potentially unsupported software trains.
In 2025, Cisco announced CVE-2025-20159, a critical vulnerability affecting the management interface ACL processing in Cisco IOS XR Software. This vulnerability allows an unauthenticated, remote attacker to completely bypass configured access control lists (ACLs) for SSH, NetConf, and gRPC features. This is a severe failure because management ACLs are intended to be the last line of defense, restricting which IP addresses can reach the device's management plane. A bypass renders these access rules completely ineffective.
If immediate patching is not possible, consider temporarily disabling RSA-based public key authentication if it is the primary vector for a known bypass. CVE-2020-3200 Detail - NVD
The most famous vulnerability associated with this version string is the Cisco "Small SSH" issue. Early implementations of SSH on Cisco IOS had a flaw in the key exchange mechanism. In certain configurations, an attacker could bypass authentication entirely. If a device reports this version string, it is highly likely susceptible to authentication bypass, allowing an attacker to gain administrative access without a password.
The SSH-2.0-Cisco-1.25 vulnerability is a serious security issue that requires immediate attention. By understanding the vulnerability and taking steps to mitigate it, organizations can protect their Cisco devices and prevent potential security breaches.
Moral: Treat unexpected SSH banners as a signal to investigate, not ignore. With containment, identification, mitigations, timely patching, and improved processes, small teams can keep critical infrastructure safe.
Devices exposing this banner generally span several generations of Cisco software, making them vulnerable to several critical flaws depending on the exact implementation.