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Authentication Bypass in Gitea Docker Reverse Proxy Authentication

IdentifiersCVE-2026-20896CWE-346

CVE-2026-20896 is a critical authentication bypass affecting official Gitea Docker images through version 1.26.2. Gitea supports reverse-proxy-based authentication using the X-WEBAUTH-USER header when requests originate from trusted proxies. The documented secure default for REVERSE_PROXY_TRUSTED_PROXIES is loopback-only (127.0.0.0/8,::1/128), but affected Docker images shipped with REVERSE_PROXY_TRUSTED_PROXIES = * in the default configuration template. In deployments where ENABLE_REVERSE_PROXY_AUTHENTICATION is enabled, this causes Gitea to trust authentication headers from any source IP rather than only from a legitimate upstream proxy. As a result, a remote attacker can send a crafted X-WEBAUTH-USER header directly to the Gitea instance and be authenticated as an arbitrary user, including an administrator. The issue is described as affecting Docker deployments; source-built Gitea instances using the standard sample configuration are reported as not affected.

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ANALYST BRIEF

Impact, mitigation & remediation

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Impact

What an attacker gets, and what they’ve been doing with it.

Successful exploitation allows complete authentication bypass and user impersonation. An attacker can log in as any existing user, including administrators, and then perform actions available to that account. Reported consequences include administrator account takeover, modification of SSH keys, disabling of 2FA, export or access to private repositories, and redirection or modification of webhook URLs. Where administrative access is obtained, the vulnerability can lead to full compromise of the Gitea instance and its hosted source code, secrets, and integration settings.

Mitigation

If you can’t patch tonight, do this now.

If immediate upgrade is not possible, disable ENABLE_REVERSE_PROXY_AUTHENTICATION unless it is strictly required. Explicitly set REVERSE_PROXY_TRUSTED_PROXIES to only trusted proxy addresses instead of '*'. Ensure the Gitea service is not directly reachable from untrusted networks when reverse proxy authentication is in use, and enforce network controls so only the intended reverse proxy can connect to the application. If ENABLE_REVERSE_PROXY_AUTO_REGISTRATION is enabled, disable it unless operationally necessary. Review logs and account activity for suspicious header-based logins, unexpected account creation, SSH key changes, 2FA changes, repository exports, and webhook modifications.

Remediation

Patch, then assume compromise.

Upgrade affected Gitea Docker deployments to version 1.26.3 or later. The fix reportedly removes the wildcard trusted-proxy default from Docker images and makes reverse proxy authentication opt-in. After upgrading, verify that reverse proxy authentication is enabled only where required and that REVERSE_PROXY_TRUSTED_PROXIES is explicitly restricted to the actual IP addresses or CIDR ranges of the legitimate upstream reverse proxies.
PUBLIC EXPLOITS

Exploits

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VALID 0 / 0 TOTALView more in app

No public exploit code observed for this vulnerability.

ACTIVITY FEED

Recent activity

7 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.

7 SOURCESView more in app
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Threat actor evidence

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Associated malware

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Detection signatures

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Vendor-by-vendor mapping

Cross-references every affected SKU, including bundled OEM variants.

Social activity5

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EXTERNAL REFERENCES
MITRE CVE
cve.org · CVE-2026-20896
NVD
nvd.nist.gov/vuln/detail/CVE-2026-20896
MITRE CWE · CWE-346
cwe.mitre.org