9.3

CVSS Score

4.0

-

CVSS Score

Basic Information

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CVE-2025-4658

CVE-2025-4658: OPKSSH Vulnerable to Authentication Bypass

Impact

Versions of OpenPubkey library prior to 0.10.0 contained a vulnerability that would allow a specially crafted JWS to bypass signature verification. As OPKSSH depends on the OpenPubkey library for authentication, this vulnerability in OpenPubkey also applies to OPKSSH versions prior to 0.5.0 and would allow an attacker to bypass OPKSSH authentication.

Patches

The vulnerability does not exist in more recent versions of OPKSSH. his only impacts OPKSSH when used to verify ssh keys on a server, the OPKSSH client is unaffected. To remediate upgrade to a version of OPKSSH v0.5.0 or greater.

To determine if you are vulnerable run on your server:

opkssh --version

If the version is less than 0.5.0 you should upgrade. To upgrade to the latest version run:

wget -qO- "https://raw.githubusercontent.com/openpubkey/opkssh/main/scripts/install-linux.sh" | sudo bash

References

CVE-2025-4658

The upstream vulnerability in OpenPubkey is CVE-2025-3757 and has the security advisory https://github.com/openpubkey/openpubkey/security/advisories/GHSA-537f-gxgm-3jjq

(GitHub Advisory)

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CVE-2025-4658

CVE-2025-4658:

9.3

CVSS Score

4.0

-

CVSS Score

Basic Information

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Technical Details

Package Name	Ecosystem	Vulnerable Versions	First Patched Version
github.com/openpubkey/opkssh	go	< 0.5.0	0.5.0

Technical Details

Vulnerability Intelligence
Miggo AI

Root Cause Analysis

The vulnerability GHSA-56wx-66px-9j66 in opkssh is an authentication bypass due to its use of a vulnerable version of the 'openpubkey/openpubkey' library (specifically, versions prior to 0.10.0, as per GHSA-537f-gxgm-3jjq). The advisory states this affects opkssh when used to verify SSH keys on a server.

The fix in opkssh involves updating this dependency. I analyzed the commits between the last known vulnerable version of opkssh (v0.4.0, commit fd59ad413fd6ef35bd356cc9c5063b1dd1e2bbec) and the first patched version (v0.5.0, commit 9d5af7a074c2e2d84b0b154da41b476d8f2b4e4e).

Commit acd42b63700a53cd7513890c5d9990ae3d904fee (titled 'Add support for ES256 OpenID Providers (#135)') contains the crucial change: it updates github.com/openpubkey/openpubkey from v0.8.0 to v0.10.0 in go.mod and go.sum. This is the direct mitigation for the vulnerability within opkssh.

The vulnerable functions in opkssh are those that invoke the signature verification capabilities of the (previously vulnerable) openpubkey library. This primarily occurs during the opkssh verify command, which is typically configured as the AuthorizedKeysCommand on an SSH server.

Therefore, the Run method of the VerifyCmd struct (likely in commands/verify.go) is the most directly relevant function in opkssh that would have processed potentially malicious input via the vulnerable library. The main function, when dispatching to the verify command, is also part of this vulnerable execution path.

The confidence is 'medium' because while the dependency update is clear, the exact function names within opkssh are inferred based on common Go CLI application structure and the description of the vulnerability, rather than explicit code changes to those functions themselves within the patch (as the patch is a dependency update).

Vulnerable functions

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WAF Rule

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Reasoning

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