CVE-2026-101027 in Gitea
Summary
by MITRE • 10/06/2026
When `[migrations] ALLOWED_DOMAINS` was configured, a hostname matching the allow list was accepted without checking its resolved address against the local-network restrictions. A user who can start repository migrations and control the DNS of an allowed hostname could make it resolve to loopback or private addresses and bypass `ALLOW_LOCALNETWORKS = false`, reaching internal services from the Gitea server. Instances without `ALLOWED_DOMAINS` configured are not affected by this specific bypass.
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Analysis
by VulDB Data Team • 10/07/2026
The vulnerability described constitutes a critical authentication and authorization bypass within the repository migration functionality of Gitea, specifically affecting instances where the ALLOWED_DOMAINS configuration parameter is utilized to restrict which external hosts can be migrated from. This flaw arises from an incomplete validation process during the initial phase of the migration workflow. When a user initiates a migration request for a repository hosted on a domain listed in the allowed domains whitelist, the application performs a superficial check that verifies only the hostname string against the configuration list. Crucially, this verification step fails to resolve the hostname to its corresponding IP address before proceeding with the connection attempt or further security checks. This architectural oversight creates a significant gap between the intended policy of restricting access to local networks and the actual operational behavior when DNS manipulation is possible.
The technical flaw leverages the trust placed in domain name resolution without verifying the underlying network topology. By controlling the Domain Name System records for an allowed hostname, an attacker can direct the Gitea server to resolve that domain to a loopback address such as 127.0.0.1 or to private IP ranges like 192.168.x.x or 10.x.x.x. Since the initial allow-list check passes based on the hostname alone, the subsequent connection attempt is permitted even if ALLOW_LOCALNETWORKS is set to false. This effectively neutralizes the local network restriction mechanism, allowing external users who have permission to start migrations to probe and interact with internal services that are otherwise protected from outside access. The impact extends beyond simple data exfiltration; it enables potential reconnaissance of internal infrastructure, exploitation of vulnerable internal web applications via SSRF-like patterns inherent in migration tools, or unauthorized access to sensitive backend systems residing on the local network segment.
From a classification perspective, this vulnerability aligns with CWE-20 Improper Input Validation and CWE-918 Server-Side Request Forgery (SSRF). The failure to validate that the resolved IP address adheres to security policies regarding private or loopback ranges is a classic example of input validation bypass where only part of the input context is checked. In terms of offensive cybersecurity frameworks, this behavior maps directly to ATT&CK technique T1557 Adversary-in-the-Middle and specifically T1090 Proxy, as it allows an attacker to use the vulnerable application as a proxy to reach internal resources that are not publicly accessible. The attack vector relies on DNS manipulation, which falls under reconnaissance or initial access phases depending on whether the attacker controls the DNS infrastructure directly or exploits misconfigured records elsewhere in their environment.
The operational impact is severe for organizations relying on Gitea's migration features while maintaining strict network segmentation policies. An authenticated user with limited privileges who can trigger repository migrations gains a foothold to pivot into the internal network. This could lead to unauthorized access to databases, internal APIs, or management interfaces that are not exposed to the public internet but were assumed safe due to the ALLOW_LOCALNETWORKS setting. The risk is particularly acute in environments where Gitea servers have broader network connectivity than intended, such as those placed on a DMZ with limited but non-zero access to backend services. Instances without the ALLOWED_DOMAINS configuration are not susceptible to this specific bypass because they do not rely on hostname-based allow lists that can be manipulated via DNS resolution tricks in the same manner; however, general SSRF protections should still be rigorously tested across all migration endpoints regardless of configuration.
Mitigation strategies must address both immediate remediation and long-term architectural improvements. The primary fix involves modifying the migration logic to resolve hostnames to IP addresses immediately upon receiving a request and validating those IPs against local network ranges before allowing any connection attempts, even if the hostname is whitelisted. This ensures that the ALLOW_LOCALNETWORKS restriction applies consistently regardless of DNS configuration. Administrators should also consider implementing strict egress filtering at the firewall level for Gitea servers to prevent outbound connections to private IP ranges entirely, providing a defense-in-depth layer independent of application logic. Additionally, enabling comprehensive logging and monitoring for migration activities can help detect anomalous resolution patterns or attempts to access internal endpoints. Until patches are applied, restricting who has permission to initiate migrations is the most effective temporary control measure to limit exposure to this vulnerability.