Security Digest · Vulnerability record
CVE-2025-4658: OPKSSH Vulnerable to Authentication Bypass
Versions of OpenPubkey library prior to 0.10.0 contained a vulnerability that would allow a specially crafted JWS to bypass signature verification.
CVSS 9.3 Critical EPSS 0.3% · p26
Should you act?
Critical and remotely reachable
No known exploitation yet, but it is network-reachable without credentials. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.
- No confirmed exploitation. It is not in CISA’s KEV catalog and CISA’s SSVC assessment records no known exploitation. That can change quickly after a public write-up; re-check if you are affected.
- EPSS 0.3%, percentile 26: FIRST’s model estimates a 0.3% chance of exploitation activity in the next 30 days, higher than 26% of all scored CVEs (low). EPSS is a probability, not a verdict.
- Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
- Only applies if your dependency tree includes
github.com/openpubkey/opkssh(Go) < 0.5.0, fixed in 0.5.0. Check your lockfile, including transitive dependencies.
What it is
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.
From the GitHub advisory
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:
Weakness type: CWE-305.
Product: github.com/openpubkey/opkssh (Go) · Assigned by: cloudflare · Published: 2025-05-13
Affected and fixed versions
| Ecosystem | Package | Vulnerable | First fixed |
|---|---|---|---|
| Go | github.com/openpubkey/opkssh | < 0.5.0 | 0.5.0 |
| Vendor | Product | Affected versions (per CVE record) |
|---|---|---|
| OPKSSH | OPKSSH | 0.1.0 <= 0.4.0 |
Severity scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| cloudflare | 4.0 | 9.3 Critical | CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:L/SI:L/SA:L |
| GitHub | 4.0 | 9.3 | CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:L/SI:L/SA:L |
- Attack vector: network (remotely reachable)
- Attack complexity: low
- Attack requirements: none
- Privileges required: none (no login)
- User interaction: none
CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.
Exploitation and urgency
- CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
- CISA SSVC assessment: exploitation none, automatable yes, technical impact total.
- FIRST EPSS (model of 2026-10-21): 0.34% probability of exploitation activity in the next 30 days; percentile 26.
Timeline
- — CVE record last updated
- — CVE record published by cloudflare
- — GitHub-reviewed advisory GHSA-56wx-66px-9j66 published (critical)
Sources and references
Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.
Vulnerability records
- GitHub Advisory GHSA-56wx-66px-9j66 github.com
- CVE.org record CVE-2025-4658 cve.org
- NVD entry CVE-2025-4658 nvd.nist.gov
Other references from the CVE record and advisory
- github.com github.com
- github.com github.com