Vulnerability in github.com/fabiolb/fabio (CVE-2026-62987)
Summary
Vulnerability in github.com/fabiolb/fabio (CVE-2026-62987). Risk of unauthorized operations or information disclosure. Exploitable via Connection. Mitigation: upgrade to 1.6.6 or later.
Original description
The description as published by the source.
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:73r.Header.Set(cfg.ClientIPHeader, remoteIP) - TLSHeader (
proxy.header.tls) - http_headers.go:153r.Header.Set(cfg.TLSHeader, cfg.TLSHeaderValue)(TLS connections) - RequestID (
proxy.header.requestid) - http_proxy.go:90r.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.Dels 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,…
Source: NIST National Vulnerability Database NVD GitHub Advisory
Auto-generated summary
Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.
A vulnerability tracked as CVE-2026-62987 has been found in github.com/fabiolb/fabio.
Attackers can target a specific entry point like Connection over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 5.8/10.
What to do: upgrade github.com/fabiolb/fabio to 1.6.6 or later.
If unsure, ask your IT team or search "github.com/fabiolb/fabio CVE-2026-62987" on the vendor's site.
CVE-2026-62987 (github.com/fabiolb/fabio) — CWE-290 / CVSS v3 5.8
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: Connection / protectHeaders / proxy.header.clientip / proxy.header.tls
Patched: 1.6.6 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.
A vulnerability (CWE-290) exists in github.com/fabiolb/fabio. Attackers reach the vulnerable code path via Connection without authentication.
Check the vendor advisory for the affected versions of github.com/fabiolb/fabio. Attack surface: Connection / protectHeaders / proxy.header.clientip / proxy.header.tls.
Severity: Medium (CVSS 5.8/10). Risk of unauthorized operations or information disclosure.
Update to 1.6.6.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'github.com/fabiolb/fabio' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.
Response actions
Concrete steps and command examples for SOC/SRE teams to execute in order
-
1Identify exposure identify
grep -r 'github.com/fabiolb/fabio' . | grep -v node_modulesリポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で
github.com/fabiolb/fabioを grep し、稼働しているサービス・バージョンを把握する。 -
2Apply patch patch
Upgrade github.com/fabiolb/fabio to 1.6.6ステージング環境で 1.6.6 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。
-
3Post-deployment verification verify
Confirm patched version is live in productionパッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。
Affected packages
References
- advisory nvd.nist.gov
- package github.com
- web github.com
- web github.com
- web github.com
- web github.com