CVE-2026-48113

Received Received - Intake

Authenticated Client Bypass in Chisel TCP/UDP Tunnel

Publication date: 2026-08-03

Last updated on: 2026-08-03

Assigner: GitHub, Inc.

Description

Chisel is a TCP/UDP tunnel, transported over HTTP and secured via SSH. In versions prior to 1.11.5, authenticated clients can bypass --authfile ACL restrictions and tunnel traffic to arbitrary destinations reachable from the server. The ACL is enforced only during the initial handshake against declared remotes, but never on subsequent SSH channels that carry actual traffic. A malicious client can authenticate with a permitted remote, then open channels to any host:port it wants. This issue has been fixed in version 1.11.5.

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Meta Information

Published

2026-08-03

Last Modified

2026-08-03

Generated

2026-08-04

AI Q&A

2026-08-04

EPSS Evaluated

N/A

NVD

CVE-2026-48113

Affected Vendors & Products

Vendor	Product	Version / Range
chisel	chisel	to 1.11.5 (exc)

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-863	The product performs an authorization check when an actor attempts to access a resource or perform an action, but it does not correctly perform the check.

Attack-Flow Graph

Executive Summary

Chisel is a TCP/UDP tunnel secured via SSH. In versions before 1.11.5, authenticated users can bypass access control lists (ACL) meant to restrict tunnel destinations. The ACL is only checked during initial setup, not for ongoing traffic. Attackers can exploit this to route traffic to any server reachable by the Chisel server after authenticating with a permitted remote.

Detection Guidance

Detecting this vulnerability requires monitoring for unauthorized SSH tunnels or traffic bypassing ACL restrictions. Check Chisel server logs for connections from authenticated clients opening channels to unexpected destinations. Use network monitoring tools like tcpdump or Wireshark to inspect traffic for unusual SSH channel usage. Verify if clients are tunneling to hosts outside the permitted remotes listed in --authfile.

Impact Analysis

If you run a vulnerable Chisel server, attackers could use it to bypass your intended network restrictions. This could allow unauthorized access to internal systems, data exfiltration, or launching attacks from your server. The impact depends on your network configuration and what systems the Chisel server can reach.

Compliance Impact

This vulnerability could lead to unauthorized network access or data breaches, violating compliance requirements like GDPR's data protection principles or HIPAA's access controls. Organizations may face penalties if this flaw enables exposure of protected data. Immediate patching is recommended to maintain compliance.

Mitigation Strategies

Upgrade Chisel to version 1.11.5 or later immediately to patch the ACL bypass issue. If upgrading is not possible, restrict network access to the Chisel server to prevent unauthorized clients from connecting. Review and tighten firewall rules to block unexpected outbound traffic from the server. Monitor logs for any signs of exploitation attempts.

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