# CVE-2026-35388: OpenSSH connection multiplexing confirmation bypass in proxy mode

Source: https://junglewise.ai/threats/cve-2026-35388-openssh-connection-multiplexing-confirmation-bypass-in-proxy-mode  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-04-02. Updated: 2026-07-24  
License: CC BY 4.0 with a link back

CVE-2026-35388 · Severity: low · CVSS 2.5 · Published 2026-04-02

OpenSSH is a widely used suite of secure networking utilities for remote login and file transfer. A security flaw was identified where the system failed to ask for user confirmation when a new connection attempted to join an existing shared session in 'proxy mode.' This could allow an unauthorized local process to hijack a user's active connection without their knowledge, though it requires specific configurations to be active.

Technologies: [OpenBSD Openssh](https://junglewise.ai/threats/technologies/openssh). Vendors: [OpenBSD](https://junglewise.ai/threats/vendors/openbsd).

## Quick answers

**Is CVE-2026-35388 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-35388 being exploited in the wild.

**How severe is CVE-2026-35388?** Low severity, with a CVSS score of 2.5, published 2 April 2026.

**Which products and versions are affected?** OpenBSD Openssh before 10.3.

**Is there a fix for CVE-2026-35388?** A patch was published on 2026-04-02: OpenSSH 10.3 released fixing the issue. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-35388 attacked?** It is attacked with local access, in a software library.

**Am I affected by CVE-2026-35388?** Check whether you run OpenBSD Openssh 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.

## Technical details

A vulnerability exists in OpenSSH's connection multiplexing feature (ControlMaster). When 'ControlMaster ask' or 'autoask' is configured, the client is intended to prompt the user for confirmation before allowing a new session to join the existing multiplexed connection. However, in versions prior to 10.3, this confirmation check was omitted for proxy-mode multiplexing sessions (invoked via 'ssh -O proxy'). A local attacker or malicious process on the same client machine could exploit this to join an existing SSH multiplexing socket without the legitimate user being prompted to allow the connection. This issue is tracked as CWE-420 (Unprotected Alternate Channel). The fix was introduced in OpenSSH 10.3.

## Affected products

- OpenBSD OpenSSH before 10.3

## Timeline

- 2026-04-02: disclosed: Vulnerability disclosed in OpenSSH 10.3 release notes.
- 2026-04-02: patched: OpenSSH 10.3 released fixing the issue.

## References

- [https://marc.info/?l=openssh-unix-dev&m=177513443901484&w=2](https://marc.info/?l=openssh-unix-dev&m=177513443901484&w=2)
- [https://www.openssh.org/releasenotes.html](https://www.openssh.org/releasenotes.html)
- [https://www.openwall.com/lists/oss-security/2026/04/02/3](https://www.openwall.com/lists/oss-security/2026/04/02/3)

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- [In sshd in OpenSSH before 10.5, the restrict keyword (in authorized_keys) was supposed to be applicable to tunnel forwarding but was not.](https://junglewise.ai/threats/cve-2026-73283-in-sshd-in-openssh-before-10-5-the-restrict-keyword-in-authorized)
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