Overview
CVE-2025-58181 is a medium severity vulnerability affecting SSH servers. It stems from improper validation of the number of mechanisms specified in GSSAPI authentication requests. An attacker can exploit this flaw by sending a specially crafted request with an excessive number of mechanisms, leading to unbounded memory consumption on the server and potentially causing a denial-of-service (DoS).
Technical Details
The vulnerability resides in the GSSAPI authentication handling logic of SSH servers. During GSSAPI authentication, the client sends a list of supported mechanisms to the server. The server then iterates through this list to find a mutually supported mechanism. However, if the server doesn’t properly validate the size of this list, an attacker can send a request containing an extremely large number of mechanisms. This can cause the server to allocate an excessive amount of memory while processing the request, leading to resource exhaustion.
This vulnerability impacts implementations that use the affected Golang libraries for handling SSH and GSSAPI. It was identified as GO-2025-4134 within the Go vulnerability database.
CVSS Analysis
- Severity: MEDIUM
- CVSS Score: 5.3
The CVSS score of 5.3 indicates a medium severity vulnerability. While it doesn’t allow for arbitrary code execution, the potential for denial of service through memory exhaustion makes it a significant concern. The exploit complexity is considered low, as crafting the malicious GSSAPI request is relatively straightforward.
Possible Impact
The primary impact of CVE-2025-58181 is a denial-of-service (DoS). A successful exploit can cause the SSH server to become unresponsive, preventing legitimate users from connecting. In severe cases, it could lead to a system crash if the server exhausts all available memory.
Mitigation or Patch Steps
The recommended mitigation is to update the affected SSH server software to a patched version. If your SSH server uses Go libraries, ensure you are using versions that include the fix. Specifically, refer to the following resources for updates:
- Review and apply the fix described in Go Change List 721961
- Monitor the Go issue tracker for updates: Go Issue 76363
- Check the golang-announce mailing list for related announcements.
If patching is not immediately feasible, consider temporarily disabling GSSAPI authentication as a workaround, though this may impact users who rely on this authentication method.
