CVE-2026-48113 in Chisel
Summary
by MITRE • 08/04/2026
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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Analysis
by VulDB Data Team • 08/04/2026
The Chisel vulnerability represents a critical access control bypass flaw that undermines the security model of the tunneling application. This issue affects versions prior to 1.11.5 and demonstrates a fundamental failure in the implementation of authentication and authorization mechanisms. The vulnerability stems from a design flaw where access control lists are only enforced during the initial SSH handshake phase but not maintained throughout subsequent communication channels. This architectural weakness creates an opportunity for authenticated users to escalate their privileges and gain unauthorized network access beyond the intended scope defined by the --authfile configuration.
The technical implementation of this vulnerability exploits the separation between authentication and authorization enforcement within the SSH tunneling framework. During the initial connection handshake, Chisel validates client credentials against the configured ACL rules and permits connections to specified remote destinations. However, once authenticated, the system fails to validate subsequent SSH channels that carry actual data traffic against the original access restrictions. This gap in validation allows malicious actors to establish new channels to any network destination accessible from the server host, effectively bypassing all intended security boundaries. The flaw operates at the protocol level where legitimate authentication credentials are used to gain initial access, but the authorization controls are not consistently enforced across all communication sessions.
The operational impact of this vulnerability extends beyond simple privilege escalation to encompass potential network reconnaissance and lateral movement capabilities. An attacker with valid credentials can leverage this flaw to probe internal networks, access services that were never intended for their access level, and potentially exfiltrate sensitive data from systems within the trusted network perimeter. This vulnerability undermines the core security principle of least privilege by allowing authenticated users to bypass the ACL restrictions that protect network segments and services. The implications are particularly severe in environments where Chisel is used to provide secure remote access to internal infrastructure, as it could enable attackers to move laterally across the network without detection.
Mitigation strategies for this vulnerability require immediate patching to version 1.11.5 or later, which implements proper channel validation and maintains ACL restrictions throughout all communication sessions. Organizations should also implement additional monitoring of Chisel service usage, particularly around authentication events and connection patterns that might indicate unauthorized access attempts. Network segmentation and firewall rules should be reviewed to limit the exposure of Chisel servers to unnecessary network segments. The vulnerability aligns with CWE-284 (Improper Access Control) and can be categorized under ATT&CK technique T1071.002 (Application Layer Protocol: DNS) when used for exfiltration purposes, or T1566 (Phishing) if the initial compromise occurs through credential theft. Security teams should also consider implementing behavioral analytics to detect anomalous tunneling activities that deviate from normal usage patterns and could indicate exploitation of this access control bypass.