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The CVE-2025-58181 vulnerability exists within SSH server implementations that support GSSAPI (Generic Security Services Application Program Interface) for authentication. During the initial authentication handshake, a client can send a GSSAPI authentication request containing a list of proposed security mechanisms. The server’s parsing function is designed to read this list and iterate through each mechanism to find a compatible one. However, a critical validation step is missing: the server fails to check the numerical value specifying the count of mechanisms in the incoming request. An attacker can exploit this by crafting a malicious request that declares an excessively high or unrealistic number of mechanisms, such as an integer maximum value. When the vulnerable server parses this request, it blindly trusts the client-supplied count. It then enters a loop to process each claimed mechanism, dynamically allocating memory structures for every entry. Since there is no upper bound enforced, the server attempts to allocate memory for millions or billions of non-existent mechanisms. This leads to uncontrolled and unbounded memory consumption on the host system. The memory allocation happens rapidly during the parsing phase, before any substantive authentication occurs. Consequently, the server’s available RAM is quickly exhausted, causing severe performance degradation. In many cases, this forces the server process to crash or become completely unresponsive, resulting in a denial-of-service condition. The attack is remote and can be executed without valid user credentials, as it targets the authentication negotiation layer itself. The flaw is particularly dangerous because a single malicious packet can trigger the memory exhaustion. Repeated attacks can compound the effect, making service restoration difficult. This vulnerability is rooted in improper input sanitization and a lack of safe programming practices for handling network data. Implementations written in the Go language, as referenced by the source, are confirmed to be affected by this parsing logic error. Mitigation requires patching the SSH server code to add strict bounds checking on the mechanism count field. System administrators must apply vendor updates to limit memory allocation and prevent this exploitable condition.
DailyCVE Form:
Platform: Go SSH Implementations
Version: Unspecified affected versions
Vulnerability: Unbounded memory consumption
Severity: High
date: 11/19/2025
Prediction: Expected 2025-12-20
What Undercode Say:
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!/bin/bash
Simulate malicious GSSAPI request count
echo “Simulating high mechanism count…”
python3 -c “
import struct
Craft SSH userauth request with giant mechanism count
payload = struct.pack(‘>I’, 0xFFFFFFFF) Invalid large number
print(‘Payload crafted:’, payload.hex())
”
Network send command (commented out)
nc -v [bash] 22 < malicious_packet.bin
How Exploit:
Attacker crafts a SSH packet with a manipulated GSSAPI mechanism list field. The packet sets the mechanism count to an extremely high integer value (e.g., 4294967295). This packet is sent to the target SSH server during authentication. The server parses the count and allocates memory for each entry until resources are exhausted.
Protection from this CVE
Apply vendor patches. Disable GSSAPI authentication if unused. Implement network access controls. Use intrusion detection systems.
Impact:
Denial-of-service condition. System memory exhaustion. Service unavailability for legitimate users. Potential for repeated exploitation cycles.
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Sources:
Reported By: nvd.nist.gov
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