Fabio - Incomplete fix for CVE-2025-48865: operator-configured trust headers (clientip/tls/requestid) still strippable via the Connection header
**Affected:** github.com/fabiolb/fabio >= 1.6.6 through 1.7.1 and master HEAD (c75f8a6). ### Summary The v1.6.6 fix for CVE-2025-48865 sweeps the client `Connection` header against a hardcoded allowlist `protectHeaders` (proxy/http_headers.go:28-36) containing only the 7 X-Forwarded family headers. Fabio also injects three *operator-configured* server-side trust headers that are NOT in that allowlist, so the original hop-by-hop stripping attack still works against them. ### Details The three unprotected trust headers and where fabio sets them: - ClientIPHeader (`proxy.header.clientip`) - http_headers.go:73 `r.Header.Set(cfg.ClientIPHeader, remoteIP)` - TLSHeader (`proxy.header.tls`) - http_headers.go:153 `r.Header.Set(cfg.TLSHeader, cfg.TLSHeaderValue)` (TLS connections) - RequestID (`proxy.header.requestid`) - http_proxy.go:90 `r.Header.Set(p.Config.RequestID, id())` Order of operations in HTTPProxy.ServeHTTP: (1) line 90 sets RequestID; (2) line 175 calls addHeaders, which sweeps the Connection header (keeping the three configured names because they are absent from protectHeaders) and then sets ClientIPHeader/TLSHeader; (3) line 223 runs the Go `httputil.ReverseProxy`, whose `removeHopByHopHeaders` (Go stdlib net/http/httputil/reverseproxy.go) iterates the inbound `Connection` header and `h.Del`s every listed header. The three trust headers fabio just set are therefore deleted before the request reaches the backend. ### PoC Configure `proxy.header.clientip=X-Client-IP`, `pr
GO-2026-6566
Revision 1
Fabio - Incomplete fix for CVE-2025-48865: operator-configured trust headers (clientip/tls/requestid) still strippable via the Connection header in github.com/fabiolb/fabio
Fabio - Incomplete fix for CVE-2025-48865: operator-configured trust headers (clientip/tls/requestid) still strippable via the Connection header in github.com/fabiolb/fabio
Imported from structured advisory data. Source references identify upstream records or fields; verify affected versions and your deployed configuration.
Security context
Source reference: osv:GO-2026-6566
github.com/fabiolb/fabio
Source reference: /affected/0/package/name
- Affected versions
- Not stated in this record
- Fixed versions
- 1.7.2
Source reference:
/affected/0/ranges - Prerequisites
- Not stated in this record
Structured affected-version data
Original package identities and version rules from this source.
[
{
"ranges": [
{
"type": "SEMVER",
"events": [
{
"introduced": "1.6.6"
},
{
"fixed": "1.7.2"
}
]
}
],
"package": {
"name": "github.com/fabiolb/fabio",
"purl": "pkg:golang/github.com/fabiolb/fabio",
"ecosystem": "Go"
},
"database_specific": {
"source": "https://vuln.go.dev/ID/GO-2026-6566.json"
},
"ecosystem_specific": {
"imports": [
{
"path": "github.com/fabiolb/fabio",
"symbols": [
"main",
"newHTTPProxy"
]
},
{
"path": "github.com/fabiolb/fabio/proxy",
"symbols": [
"HTTPProxy.ServeHTTP",
"addHeaders"
]
}
]
}
}
]- Related CVEs
- CVE-2026-62987
Source reference:
/aliases
Publisher severity
No explicit severity was provided.
- Event
- #63841 · Revision 1
- Added to Heist Feed
- Publisher date
GHSA-fq95-v8xc-jm3v
Primary source · Revision 1
Imported from structured advisory data. Source references identify upstream records or fields; verify affected versions and your deployed configuration.
Security context
Source reference: osv:GHSA-fq95-v8xc-jm3v
github.com/fabiolb/fabio
Source reference: /affected/0/package/name
- Affected versions
- Not stated in this record
- Fixed versions
- 1.7.2
Source reference:
/affected/0/ranges - Prerequisites
- Not stated in this record
Structured affected-version data
Original package identities and version rules from this source.
[
{
"ranges": [
{
"type": "SEMVER",
"events": [
{
"introduced": "1.6.6"
},
{
"fixed": "1.7.2"
}
]
}
],
"package": {
"name": "github.com/fabiolb/fabio",
"purl": "pkg:golang/github.com/fabiolb/fabio",
"ecosystem": "Go"
},
"database_specific": {
"source": "https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/09/GHSA-fq95-v8xc-jm3v/GHSA-fq95-v8xc-jm3v.json",
"last_known_affected_version_range": "<= 1.7.1"
}
}
]- Related CVEs
- CVE-2026-62987
Source reference:
/aliases
Publisher severity
No explicit severity was provided.
- Event
- #63878 · Revision 1
- Added to Heist Feed
- Publisher date