CVE-2026-27779: Gitea 1.25.5 URL Spoofing Vulnerability – Patch Guide

Technical summary

The vulnerability exists in Gitea's URL detection logic when processing the X-Forwarded-Proto (or similar forwarded protocol) header. Versions before 1.25.5 fail to properly sanitize or validate this header value before using it to construct canonical URLs. An unauthenticated remote attacker can exploit this by sending crafted HTTP requests with malformed forwarded-proto values, causing Gitea to generate spoofed or invalid canonical URLs. This results in a denial-of-availability condition rather than confidentiality or integrity breach of repository data.

Business impact

Organizations running self-hosted Gitea instances may experience service degradation or availability issues if attackers exploit this vulnerability to generate malformed URLs. This could disrupt developer workflows, CI/CD pipelines, and Git operations that depend on correct canonical URL resolution. Downstream systems that rely on Gitea's URL generation for authentication, notifications, or integrations may also malfunction. While not a direct data breach vector, the availability impact can be significant in organizations where Gitea is a critical development infrastructure component.

Affected systems

Gitea instances running versions before 1.25.5 are vulnerable. The flaw affects all deployments—whether behind a reverse proxy, load balancer, or exposed directly—since the X-Forwarded-Proto header handling is a core component of Gitea's URL generation. Verify your Gitea version in the admin panel (typically found under Site Administration > Configuration). Organizations using Gitea as their primary Git hosting platform should prioritize assessment.

Exploitability

This vulnerability requires no authentication and can be triggered by sending a single HTTP request with a crafted forwarded-proto header value. The attack surface is the public-facing Gitea instance itself; no special user interaction is needed. The CVSS 3.1 score of 7.5 (HIGH) reflects the high accessibility and severity of the availability impact, though the attack does not directly compromise confidentiality or allow privilege escalation. Exploitation is straightforward for attackers with network access to the Gitea service.

Remediation

Upgrade Gitea to version 1.25.5 or later. This release includes validation logic to reject or safely handle malformed forwarded-proto header values. Organizations should also review and enforce strict reverse-proxy configurations to limit which upstream sources can inject X-Forwarded-Proto headers; configure your proxy to strip this header from untrusted clients and only accept it from known internal load balancers or proxies.

Patch guidance

Apply Gitea 1.25.5 or later as soon as possible. Verify the patch by checking the version displayed in Gitea's administrative interface (Admin > Configuration) or via the command line (`gitea --version`). Before upgrading, back up your Gitea database and configuration files. If you maintain a reverse proxy in front of Gitea, ensure it is configured to either strip untrusted X-Forwarded-Proto headers or validate them against an allowlist of expected protocols (http or https). Test URL generation in your environment post-upgrade to confirm canonical URLs are now correctly formed.

Detection guidance

Monitor Gitea's web logs and reverse-proxy logs for unusual X-Forwarded-Proto header values (anything other than 'http' or 'https', or repeated injection attempts). Look for HTTP 400 or 502 responses that might indicate URL parsing failures. Intrusion detection signatures should flag requests containing specially crafted or excessively long forwarded-proto values. On the host, check Gitea's version regularly and enable security update notifications from the Gitea project. Consider deploying a Web Application Firewall (WAF) rule to validate X-Forwarded-Proto values at the ingress point.

Why prioritize this

Prioritize this patch within your normal maintenance cycle. Although it carries a HIGH CVSS score and is remotely exploitable without authentication, it is not listed in CISA's Known Exploited Vulnerabilities catalog, suggesting active exploitation is not yet widespread. However, the ease of exploitation and impact on availability justify prompt patching, especially for organizations where Gitea is business-critical. If your Gitea instance is internet-exposed and handles sensitive projects, treat this as a near-term priority.

Risk score, explained

The CVSS 3.1 score of 7.5 reflects a remotely exploitable, unauthenticated attack that results in high availability impact (denial of service via URL spoofing). The vector AV:N/AC:L/PR:N/UI:N/S:U indicates network accessibility, low attack complexity, no privileges or user interaction required, and a single affected scope. The score does not account for confidentiality or integrity of repository data because the flaw does not directly expose or modify stored information—rather, it degrades service availability by breaking URL generation logic.

Frequently asked questions