CVE-2026-20896 in Gitea
Summary
by MITRE • 07/04/2026
Gitea Docker image versions up to and including 1.26.2 use REVERSE_PROXY_TRUSTED_PROXIES=* by default, allowing any source IP to impersonate a user when reverse-proxy authentication headers such as X-WEBAUTH-USER are enabled.
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Analysis
by VulDB Data Team • 07/04/2026
The vulnerability in Gitea Docker image versions up to and including 1.26.2 represents a critical authorization bypass flaw that stems from improper configuration of reverse proxy trust settings. This issue arises when the REVERSE_PROXY_TRUSTED_PROXIES parameter is set to * which effectively trusts all source IP addresses, creating an avenue for malicious actors to exploit reverse-proxy authentication mechanisms. The default configuration allows any IP address to impersonate users by simply forging authentication headers such as X-WEBAUTH-USER, fundamentally undermining the security model of the application.
This technical flaw constitutes a direct violation of access control principles and falls under CWE-284 which addresses improper access control vulnerabilities. The vulnerability enables attackers to perform privilege escalation attacks by crafting HTTP requests that include forged authentication headers, effectively allowing them to assume arbitrary user identities within the Gitea environment. The impact is particularly severe because it operates at the network level where authentication headers are processed, bypassing traditional user authentication mechanisms entirely.
The operational consequences of this vulnerability extend beyond simple unauthorized access, as it provides attackers with potential lateral movement capabilities within the system. When reverse-proxy authentication is enabled for services such as LDAP or OAuth integration, malicious actors can exploit this weakness to gain access to repositories, perform administrative actions, and potentially compromise sensitive code and configuration data. The vulnerability exists at the application layer where HTTP request processing occurs, making it particularly dangerous in containerized environments where multiple services may share the same network space.
Organizations utilizing Gitea with reverse-proxy authentication should immediately address this issue by explicitly configuring REVERSE_PROXY_TRUSTED_PROXIES to only include trusted proxy IP addresses rather than using the wildcard configuration. The recommended mitigation involves implementing specific IP address ranges or CIDR blocks that are known to be legitimate proxies rather than trusting all sources. Additionally, security teams should conduct thorough network segmentation and implement proper firewall rules to restrict access to the Gitea service to only trusted proxy servers.
From a threat modeling perspective, this vulnerability aligns with ATT&CK technique T1078 which covers valid accounts and T1566 which covers credential harvesting through social engineering or network exploitation. The attack surface is particularly wide given that many organizations deploy Gitea in containerized environments where proper network isolation may not be implemented, making the default insecure configuration especially dangerous. Organizations should also implement monitoring for suspicious authentication header usage patterns and consider implementing additional security controls such as multi-factor authentication to mitigate the risk of successful exploitation.
The vulnerability demonstrates a common pattern in containerized applications where default configurations prioritize ease of deployment over security, creating a false sense of security that leaves organizations exposed to well-known attack vectors. This issue highlights the importance of regularly reviewing application configuration settings and implementing security best practices such as the principle of least privilege. Organizations should also consider implementing automated security scanning tools that can detect such misconfigurations in their container images and deployment configurations.
From an industry compliance standpoint, this vulnerability would likely fail audit requirements for systems handling sensitive data under frameworks such as ISO 27001, NIST SP 800-53, and SOC 2. The insecure default configuration represents a failure to implement proper access control measures that are fundamental to maintaining the integrity and confidentiality of source code repositories. Security teams should also consider implementing network-level controls such as intrusion detection systems that can detect anomalous authentication header patterns indicative of exploitation attempts.
The remediation process requires careful consideration of existing network architecture and proxy configurations to ensure that the fix does not disrupt legitimate operations while properly securing the application against unauthorized access. Organizations should maintain detailed documentation of their proxy configurations and regularly audit these settings to prevent similar issues from arising in future deployments or updates. This vulnerability serves as a reminder that default security settings in popular open source tools may not be appropriate for all deployment scenarios, particularly in production environments where security controls must be explicitly defined rather than assumed.