CVE-2026-111927 in Coder
Summary
by MITRE • 10/17/2026
Coder before 2.29.20, 2.33.0 before 2.33.12, 2.34.0 before 2.34.8, and 2.35.0 before 2.35.4 contains an improper hostname validation flaw in GetWorkspaceProxyByHostname whose SIMILAR TO pattern performs a prefix match, so any domain that is a string prefix of a workspace-proxy access URL is trusted as a proxy. Attackers owning such a domain can lure an authenticated victim to a crafted /api/v2/applications/auth-redirect link, capture the redirected application_connect API key, and replay it to access the victim's workspace apps.
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Analysis
by VulDB Data Team • 10/17/2026
The vulnerability identified in Coder versions prior to 2.29.20, 2.33.12, 2.34.8, and 2.35.4 represents a critical authentication bypass mechanism rooted in improper hostname validation within the GetWorkspaceProxyByHostname function. This flaw stems from the use of a SQL SIMILAR TO pattern that executes a prefix match rather than an exact string comparison or proper domain boundary check. In practical terms, this means that if a legitimate workspace-proxy access URL is example.com, any malicious domain ending in .example.com, such as evil.example.com, will be accepted as a valid proxy host. This logic error fundamentally undermines the security model of the application by allowing attackers to register domains that are substrings or suffixes of trusted internal or external service URLs, thereby tricking the system into treating untrusted entities as authorized proxies.
The operational impact of this vulnerability is severe, enabling authenticated users who control a malicious domain to perform an account takeover-like attack against other users within the same Coder instance. An attacker can craft a specific URL pointing to /api/v2/applications/auth-redirect that includes their controlled domain in the redirect parameter. When an authenticated victim clicks or navigates to this crafted link, the application processes the request through the flawed validation logic and redirects the user's browser to the attacker-controlled domain while appending sensitive authentication tokens. Specifically, the attack allows the capture of the redirected application_connect API key, which is a high-privilege credential used for accessing workspace applications. Once captured, these credentials can be replayed by the attacker to gain unauthorized access to the victim’s workspaces and associated resources without needing further authentication steps.
From a classification perspective, this vulnerability aligns with CWE-20 Improper Input Validation, as the application fails to correctly validate user-supplied input against expected security policies regarding domain names. Furthermore, it maps directly to MITRE ATT&CK technique T1566.001 Phishing: Spearphishing Link, where an attacker lures a victim to click on a malicious link that exploits trust in the legitimate application interface. The attack vector is primarily web-based and requires initial authentication, placing it within the context of authenticated privilege escalation or credential theft via social engineering combined with technical exploitation.
Mitigation for this vulnerability involves upgrading Coder to version 2.29.20 or later, specifically versions 2.33.12+, 2.34.8+, and 2.35.4+ where the hostname validation logic has been corrected to prevent prefix-based matching attacks. In addition to software updates, administrators should enforce strict allow-listing of permitted proxy domains rather than relying on pattern-matching heuristics that can be bypassed with subdomain variations. Implementing Content Security Policy headers and monitoring for unusual redirect patterns in authentication flows can also provide additional layers of defense against similar phishing-based credential harvesting attempts.