CVE-2026-40884: goshs has an empty-username SFTP password authentication bypass

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.

• Not in CISA KEV, but CISA’s SSVC assessment records a public proof-of-concept, so attack code exists.
• EPSS 0.6%, percentile 50: FIRST’s model estimates a 0.6% chance of exploitation activity in the next 30 days, higher than 50% of all scored CVEs (moderate). 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/patrickhener/goshs (Go) <= 1.1.4, no fixed version listed; github.com/patrickhener/goshs/v2 (Go) < 2.0.0, fixed in 2.0.0. Check your lockfile, including transitive dependencies.

What it is

goshs is a SimpleHTTPServer written in Go. Prior to 2.0.0-beta.6, goshs contains an SFTP authentication bypass when the documented empty-username basic-auth syntax is used. If the server is started with -b ':pass' together with -sftp, goshs accepts that configuration but does not install any SFTP password handler. As a result, an unauthenticated network attacker can connect to the SFTP service and access files without a password. This vulnerability is fixed in 2.0.0-beta.6.

From the GitHub advisory

Summary goshs contains an SFTP authentication bypass when the documented empty-username basic-auth syntax is used. If the server is started with -b ':pass' together with -sftp, goshs accepts that configuration but does not install any SFTP password handler. As a result, an unauthenticated network attacker can connect to the SFTP service and access files without a password. I reproduced this on the latest release v2.0.0-beta.5.

Details The help text explicitly documents empty usernames as valid authentication input:

- options/options.go:264-266 says Use basic authentication (user:pass - user can be empty)

The SFTP sanity check only requires that either -b or --sftp-keyfile is present:

That parsing logic then splits -b ':pass' into an empty username and a non-empty password:

Weakness type: CWE-306.

Product: github.com/patrickhener/goshs (Go) · Assigned by: GitHub_M · Published: 2026-04-21

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Privileges required: none (no login)
• User interaction: none
• Scope: unchanged

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 poc, automatable yes, technical impact total.
• FIRST EPSS (model of 2026-10-21): 0.65% probability of exploitation activity in the next 30 days; percentile 50.

Timeline

• 2026-04-14 — GitHub-reviewed advisory GHSA-c29w-qq4m-2gcv published (critical)
• 2026-04-21 — CVE record published by GitHub_M
• 2026-04-22 — CVE record last updated

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vulnerability records

1. GitHub Advisory GHSA-c29w-qq4m-2gcv github.com
2. CVE.org record CVE-2026-40884 cve.org
3. NVD entry CVE-2026-40884 nvd.nist.gov

Other references from the CVE record and advisory

1. github.com github.com

Critical Go advisories · Today’s Security Digest