CVE-2026-27779: Gitea Auth Bypass Vulnerability

CVE-2026-27779 Overview

CVE-2026-27779 affects Gitea versions before 1.25.5. The self-hosted Git service accepts malformed or injected X-Forwarded-Proto header values when detecting the public URL. Attackers can manipulate these values to influence canonical URL generation. This leads to spoofed URLs in responses, emails, and other server-generated content. The flaw maps to CWE-284: Improper Access Control and is exploitable remotely without authentication.

Critical Impact
Unauthenticated attackers can spoof canonical URLs generated by Gitea, enabling phishing, cache poisoning, and integrity issues affecting notifications and outbound links.

Affected Products

Gitea versions prior to 1.25.5
Self-hosted Gitea instances reachable through reverse proxies
Deployments that trust forwarded headers for public URL detection

Discovery Timeline

2026-07-03 - CVE-2026-27779 published to the National Vulnerability Database (NVD)
2026-07-06 - Last updated in NVD database

Technical Details for CVE-2026-27779

Vulnerability Analysis

Gitea determines its public-facing base URL by inspecting request headers, including X-Forwarded-Proto. Versions before 1.25.5 fail to validate the header value against an expected allowlist such as http or https. An attacker sending a malformed or injected value influences how Gitea constructs canonical URLs. These URLs appear in HTTP responses, notification emails, webhook payloads, and API output.

Because the request reaches Gitea over the network with no authentication, exploitation requires only the ability to send HTTP requests to the instance. The impact is scoped to integrity of generated URLs and availability of dependent workflows rather than direct code execution or data disclosure.

Root Cause

The root cause is missing input validation on trusted forwarded headers. Gitea treats the X-Forwarded-Proto value as authoritative when constructing its canonical URL. Without a strict allowlist, attacker-controlled bytes propagate into URL builders. The upstream fixes are tracked in Gitea Pull Request #36810 and Gitea Pull Request #36836.

Attack Vector

Exploitation occurs over the network. An unauthenticated attacker sends a crafted HTTP request that includes an injected X-Forwarded-Proto value. Gitea reflects the manipulated protocol scheme into canonical URLs used across the application. Downstream systems such as mail servers, webhook consumers, and clone helpers then receive spoofed links. See the Gitea 1.25.5 release notes for the vendor description of the corrected header handling.

Detection Methods for CVE-2026-27779

Indicators of Compromise

HTTP requests containing unexpected characters, whitespace, or non-standard values in the X-Forwarded-Proto header
Gitea-generated emails or webhook payloads containing canonical URLs with malformed schemes or unexpected hostnames
Reverse proxy logs showing forwarded protocol values other than http or https

Detection Strategies

Inspect reverse proxy and web application firewall logs for anomalous X-Forwarded-* header values sent to Gitea endpoints
Correlate outbound Gitea notifications with expected ROOT_URL configuration to identify spoofed canonical links
Alert when Gitea request logs show clients supplying forwarded headers from untrusted upstream addresses

Monitoring Recommendations

Baseline the normal set of X-Forwarded-Proto values seen by the Gitea backend and alert on deviations
Monitor Gitea version banners across the fleet and flag any instance below 1.25.5
Review webhook delivery logs for URL schemes that diverge from the configured public base URL

How to Mitigate CVE-2026-27779

Immediate Actions Required

Upgrade all Gitea instances to version 1.25.5 or later using the Gitea v1.25.5 release
Restrict which upstream proxies are trusted to set forwarded headers on the Gitea server
Audit outbound notifications, webhooks, and stored URLs generated since the vulnerable version was deployed

Patch Information

Gitea 1.25.5 corrects the header parsing logic so that only well-formed protocol values are honored during public URL detection. The changes are implemented in Pull Request #36810 and Pull Request #36836. Administrators should review the 1.25.5 release notes before applying the update.

Workarounds

Configure the reverse proxy to strip or overwrite the X-Forwarded-Proto header before it reaches Gitea
Set an explicit ROOT_URL in the Gitea app.ini and disable dynamic public URL detection where possible
Restrict network access to the Gitea backend so only the trusted reverse proxy can reach it directly

bash

# Example nginx configuration to force a safe X-Forwarded-Proto value
location / {
    proxy_set_header Host              $host;
    proxy_set_header X-Real-IP         $remote_addr;
    proxy_set_header X-Forwarded-For   $proxy_add_x_forwarded_for;
    proxy_set_header X-Forwarded-Proto "https";
    proxy_pass http://gitea_backend;
}