# CVE-2026-56854: Go SSH source-address permission validation bypass in authentication callbacks

Source: https://junglewise.ai/threats/cve-2026-56854-go-ssh-source-address-permission-validation-bypass-in  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-08-28. Updated: 2026-09-25  
License: CC BY 4.0 with a link back

CVE-2026-56854 · Severity: high · CVSS 7.5 · Published 2026-08-28

An SSH authentication library in Go failed to properly validate source-address restrictions for most authentication methods. Attackers could bypass IP-based access controls set through password, keyboard-interactive, or other authentication callbacks, allowing unauthorized access from restricted IP ranges. This represents a partial failure of an intended security control, leaving organizations vulnerable even when they believed IP-based restrictions were in place.

Technologies: [golang.org/x/crypto (Go)](https://junglewise.ai/threats/technologies/golang-org-x-crypto), [golang.org/x/crypto/ssh (Go)](https://junglewise.ai/threats/technologies/golang-org-x-crypto-ssh). Vendors: [Go](https://junglewise.ai/threats/vendors/go).

## Quick answers

**Is CVE-2026-56854 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-56854 being exploited in the wild.

**How severe is CVE-2026-56854?** High severity, with a CVSS score of 7.5, published 28 August 2026.

**Which products and versions are affected?** golang.org/x/crypto (Go) SEMVER:introduced=0,fixed=0.55.0; golang.org/x/crypto/ssh (Go) prior to fix.

**Is there a fix for CVE-2026-56854?** Yes. golang.org/x/crypto (Go): upgrade to 0.55.0 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-56854 attacked?** It is attacked over the network.

**Am I affected by CVE-2026-56854?** Check whether you run golang.org/x/crypto (Go) or golang.org/x/crypto/ssh (Go) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- golang.org/x/crypto (Go): upgrade to 0.55.0 or later

  ```sh
  go get golang.org/x/crypto@v0.55.0
  ```


## Technical details

The vulnerability is a permission validation bypass in Go's SSH implementation where source-address restrictions were only enforced for PublicKeyCallback and VerifiedPublicKeyCallback authentication methods. PasswordCallback, KeyboardInteractiveCallback, NoClientAuthCallback, and GSSAPIWithMICConfig.AllowLogin callbacks silently ignored source-address restrictions in their returned Permissions objects. An attacker with valid credentials could connect from IP addresses that should have been blocked by source-address restrictions, making the control ineffective for these authentication paths. The fix applies source-address validation uniformly across all authentication callback types.

## Affected products

- Go golang.org/x/crypto/ssh prior to fix

## Identifiers

- CVE-2026-56854
- GO-2026-6303

## Timeline

- 2026-08-28: disclosed
- 2026: patched: Fix available in Go CL/797040

## References

- [https://pkg.go.dev/](https://pkg.go.dev/)
- [https://go.dev/cl/797040](https://go.dev/cl/797040)

## Related threats

- [Go SSH deadlock vulnerability in channel handling](https://junglewise.ai/threats/cve-2026-56855-go-ssh-deadlock-vulnerability-in-channel-handling)
- [Go x/crypto/ssh deadlock denial of service on undecided channel](https://junglewise.ai/threats/cve-2026-78662-go-2026-6354-prevent-dos-on-deadlocked-undecided-channel-in)
- [GO-2026-5932 - The golang.org/x/crypto/openpgp package is unmaintained, unsafe by design, and has known security issues](https://junglewise.ai/threats/go-2026-5932-the-golang-org-x-crypto-openpgp-package-is-unmaintained-7e8ca4de)
- [Go x/crypto denial of service in SSH agent Ed25519 parsing](https://junglewise.ai/threats/cve-2026-46598-go-x-crypto-denial-of-service-in-ssh-agent-ed25519-parsing)
- [Go x/crypto/ssh denial of service in AES-GCM decoder](https://junglewise.ai/threats/cve-2026-46597-go-x-crypto-ssh-denial-of-service-in-aes-gcm-decoder)